FINLUX TYPE 153 1532 28 YEAR 1985.

The FINLUX TYPE 153 1532 28 is A 28 Inches (70 Cm) Stereo and teletext color television with multistandard features .

An AV Scart socket is even present to feature more connectivity toghether with external speaker connections.

FINLUX (WAS) is a brand of consumer electronic related products, ranging from radio receivers to plasma televisions and DVD players; it was also the name of two companies that owned the brand. Over the years, the brand has been owned by several international companies. As of 2009, it is owned by the Turkish electronics manufacturer Vestel.

History

The name Finlux first appeared in 1964, when Iskumetalli began marketing TV sets with that brand name after being acquired by the Finnish Lohja conglomerate. Iskumetalli was founded in 1949 and had been manufacturing TV sets since 1958. In 1971, it was renamed Finlux; this was the first time that Finlux had been used as a company name.
In 1977, Lohja started manufacturing Electroluminescence (EL) displays after purchasing the development project, headed by Dr. Tuomo Suntola. The EL displays were manufactured using the atomic layer deposition (ALD) process developed in the project, and were marketed using Finlux brand.
In 1979, Lohja acquired another Finnish TV manufacturer, Asa Radio, which had been manufacturing radio receivers since 1927.
In 1991, the EL manufacturing was sold to Planar. A new company, Planar International was formed to continue manufacturing EL displays in Espoo, Finland. Planar later consolidated all of its EL manufacturing in Espoo and closed its Oregon EL facility.^[1]
In 1992, Finlux TV manufacturing was sold to Nokia, which already was manufacturing TV sets with brands Salora, Schaub-Lorenz and Oceanic.
In 1996, Nokia sold all its TV factories and brand names to Hong Kong company Semi-Tech, which continued manufacturing TV sets in one factory in Finland until the year 2000, when the Finnish subsidiary of Semi-Tech filed for bankruptcy.
A new company under the old Finlux name, owned by Norwegian company Otrum Electronics, was formed to continue TV manufacturing. However, they had serious troubles with their product line, which was based on CRT TVs. The market had swung to flat panel TVs and Finlux failed to switch in time. With 50 million euros in debt, the company filed for bankruptcy in September 2005.
In 2006, the Turkish electronics company Vestel, owned by the Zorlu Holding corporate group, bought the Finlux brand; it now focuses on flat panel TV sets and other consumer electronic products like DVD players/recorders and DVB sets.

Vestel, is Europe's largest and the world's third largest television manufacturer with a research and development unit of 500 employees and its plants manufacture 12 million television sets each year.
All production and other related operations in Finland have been discontinued.


Finlux was the main shirt sponsor for the Swedish team Hammarby 2008–2009.
Finlux sponsored Sheffield Wednesday Football Club from 1986 to 1989, with the unfortunate consequence that the brand name still appears on footage from the Hillsborough disaster.

References

Planar Systems, Inc. (2008). "Company History". Retrieved 2008-02-07.

FINLUX TYPE 153 1532 28 CHASSIS 1000 INTERNAL VIEW.

The FINLUX CHASSIS 1000 is developed in 2 boards carrying all functions of the tellye.

Left board - panel all signal processing and controls + teletext.

Bottom board panel all power circuits and deflections + EHT.


CIRCUITS DESCRIPTIONS:




















































FINLUX TYPE 153 1532 28  CHASSIS 1000 Supply is based on TDA4600 (SIEMENS).

Power supply Description based on TDA4601d (SIEMENS)

TDA4601 Operation. * The TDA4601 device is a single in line, 9 pin chip. Its predecessor was the TDA4600 device, the TDA4601 however has improved switching, better protection and cooler running. The (SIEMENS) TDA4601 power supply is a fairly standard parallel chopper switch mode type, which operates on the same basic principle as a line output stage. It is turned on and off by a square wave drive pulse, when switched on energy is stored in the chopper transformer primary winding in the form of a magnetic flux; when the chopper is turned off the magnetic flux collapses, causing a large back emf to be produced. At the secondary side of the chopper transformer this is rectified and smoothed for H.T. supply purposes. The advantage of this type of supply is that the high chopping frequency (20 to 70 KHz according to load) allows the use of relatively small H.T. smoothing capacitors making smoothing easier. Also should the chopper device go short circuit there is no H.T. output. In order to start up the TDA4601 I.C. an initial supply of 9v is required at pin 9, this voltage is sourced via R818 and D805 from the AC side of the bridge rectifier D801, also pin 5 requires a +Ve bias for the internal logic block. (On some sets pin 5 is used for standby switching). Once the power supply is up and running, the voltage on pin 9 is increased to 16v and maintained at this level by D807 and C820 acting as a half wave rectifier and smoothing circuit. PIN DESCRIPTIONS Pin 1 This is a 4v reference produced within the I.C. Pin 2 This pin detects the exact point at which energy stored in the chopper transformer collapses to zero via R824 and R825, and allows Q1 to deliver drive volts to the chopper transistor. It also opens the switch at pin 4 allowing the external capacitor C813 to charge from its external feed resistor R810. Pin 3 H.T. control/feedback via photo coupler D830. The voltage at this pin controls the on time of the chopper transistor and hence the output voltage. Normally it runs at Approximately 2v and regulates H.T. by sensing a proportion of the +4v reference at pin 1, offset by conduction of the photo coupler D830 which acts like a variable resistor. An increase in the conduction of transistor D830 and therefor a reduction of its resistance will cause a corresponding reduction of the positive voltage at Pin 3. A decrease in this voltage will result in a shorter on time for the chopper transistor and therefor a lowering of the output voltage and vice versa, oscillation frequency also varies according to load, the higher the load the lower the frequency etc. should the voltage at pin 3 exceed 2.3v an internal flip flop is triggered causing the chopper drive mark space ratio to extend to 244 (off time) to 1 (on time), the chip is now in over volts trip condition. Pin 4 At this pin a sawtooth waveform is generated which simulates chopper current, it is produced by a time constant network R810 and C813. C813 charges when the chopper is on and is discharged when the chopper is off, by an internal switch strapping pin 4 to the internal +2v reference, see Fig 2. The amplitude of the ramp is proportional to chopper drive. In an overload condition it reaches 4v amplitude at which point chopper drive is reduced to a mark-space ratio of 13 to 1, the chip is then in over current trip. The I.C. can easily withstand a short circuit on the H.T. rail and in such a case the power supply simply squegs quietly. Pin 4 is protected by internal protection components which limit the maximum voltage at this pin to 6.5v. Should a fault occur in either of the time constant components, then the chopper transistor will probably be destroyed. Pin 5 This pin can be used for remote control on/off switching of the power supply, it is normally held at about +7v and will cause the chip to enter standby mode if it falls below 2v. Pin 6 Ground. Pin 7 Chopper switch off pin. This pin clamps the chopper drive voltage to 1.6v in order to switch off the chopper. Pin 8 Chopper base current output drive pin. Pin 9 L.T. pin, approximately 9v under start-up conditions and 16v during normal running, Current consumption of the I.C. is typically 135mA. The voltage at this pin must reach 6.7v in order for the chip to start-up.
MC144111 6–bit D/A converters
CMOS LSI
The MC144110 and MC144111 are low–cost 6–bit D/A converters with serial
interface ports to provide communication with CMOS microprocessors and
microcomputers. The MC144110 contains six static D/A converters; the
MC144111 contains four converters.
Due to a unique feature of these DACs, the user is permitted easy scaling of
the analog outputs of a system. Over a 5 to 15 V supply range, these DACs may
be directly interfaced to CMOS MPUs operating at 5 V.
• Direct R–2R Network Outputs
• Buffered Emitter–Follower Outputs
• Serial Data Input
• Digital Data Output Facilitates Cascading
• Direct Interface to CMOS mP
• Wide Operating Voltage Range: 4.5 to 15 V
• Wide Operating Temperature Range: 0 to 85°C



TDA3505 Video control combination circuit with automatic cut-off control


GENERAL DESCRIPTION
The TDA3505 and TDA3506 are monolithic integrated circuits which perform video control functions in a PAL/SECAM
decoder. The TDA3505 is for negative colour difference signals -(R-Y), -(B-Y) and the TDA3506 is for positive colour
difference signals +(R-Y), +(B-Y).
The required input signals are: luminance and colour difference (negative or positive) and a 3-level sandcastle pulse for
control purposes. Linear RGB signals can be inserted from an external source. RGB output signals are available for
driving the video output stages. The circuits provide automatic cut-off control of the picture tube.
Features
· Capacitive coupling of the colour difference and
luminance input signals with black level clamping in the
input stages
· Linear saturation control acting on the colour difference
signals
· (G-Y) and RGB matrix
· Linear transmission of inserted signals
· Equal black levels for inserted and matrixed signals
· 3 identical channels for the RGB signals
· Linear contrast and brightness controls, operating on
both the inserted and matrixed RGB signals
· Peak beam current limiting input
· Clamping, horizontal and vertical blanking of the three
input signals controlled by a 3-level sandcastle pulse
· 3 DC gain controls for the RGB output signals (white
point adjustment)
· Emitter-follower outputs for driving the RGB output
stages
· Input for automatic cut-off control with compensation for
leakage current of the picture tube

Notes
1. < 110 mA after warm-up.
2. Values are proportional to the supply voltage.
3. When V11-24 < 0,4 V during clamping time - the black levels of the inserted RGB signals are clamped on the black
levels of the internal RGB signals.
When V11-24 > 0,9 V during clamping time - the black levels of the inserted RGB signals are clamped on an internal
DC voltage (correct clamping of the external RGB signals is possible only when they are synchronous with the
sandcastle pulse).
4. When pins 21, 22 and 23 are not connected, an internal bias voltage of 5,5 V is supplied.
5. Automatic cut-off control measurement occurs in the following lines after start of the vertical blanking pulse:
line 20: measurement of leakage current (R + G + B)
line 21: measurement of red cut-off current
line 22: measurement of green cut-off current
line 23: measurement of blue cut-off current
6. Black level of the measured channel is nominal; the other two channels are blanked to ultra-black.
7. All three channels blanked to ultra-black.
The cut-off control cycle occurs when the vertical blanking part of the sandcastle pulse contains more than 3 line
pulses.
The internal blanking continues until the end of the last measured line.
The vertical blanking pulse is not allowed to contain more than 34 line pulses, otherwise another control cycle begins.
8. The sandcastle pulse is compared with three internal thresholds (proportional to VP) and the given levels separate
the various pulses.
9. Blanked to ultra-black (-25%).
10. Pulse duration ³ 3,5 ms.


TV Stereo Decoder with Matrix TDA6600 2
SIEMENSPreliminary Data Bipolar IC
The TDA 6600-2 includes an advanced decoder for the identification signals for the
multichannel TV sound systems according to the dual-carrier system as well as a matrix
switched by the decoder to provide the L-Ft-information.
Features
0 Increased switching reliability and recognition by means of two PLLs for stereo
(117 Hz) and / or dual channel (274 Hz)
0 Separate bandwidth selection for dual-tone (pins 17-18) and stereo (pins 14-15)
0 Separate setting for the PLL time constants for dual-tone (pin 10) and stereo (pin 11)
0 Adjustable cut level for dual-tone (pin 8) and stereo (pin 9)
0 Cross-talk rejection independent of external component accuracy
0 Adjustment to minimal cross-talk level through external DC voltage
0 Suitable for TV sets with a 15625-Hz signal.
Type Ordering Code Package
TDA 6600-2 Q67000-A8210 P-DlP-24
Circuit Description
The circuitry has two functional sections:
Two phase locked loops for generating the required comparison frequencies (54.96
kHz and 54.8 kHz) from the line frequency. The phase detectors of the control loops
operate in a frequency range of 117 Hz and/or 274 Hz.
Four demodulators to evaluate the 54-kHz pilot signal. The capacitors at the mixer
outputs determine the bandwidth (and thus the signal-to-noise ratio) of the pilot tone
recognition.
An evaluation circuitry for decoding "stereo", "dual sound", and "mono" from the mixer
output levels. ln order to assure interference-free operation in case of high noise level
input signals, the individual signals "stereo" and "dual sound" are delayed via an
externally adjustable integrator. The subsequent digital evaluation provides the
information "mono", "dual sound", or "stereo" to the matrix and the 4 level input/output
(to drive the TDA 6200). If this four level input/output is connected to ground externally
(e.g. by the TDA 6200), the decoder will recognize this signal as "forced mono".
A stereo matrix with deemphasis and SCART output switched by the pilot frequency
decoder. The SCART output can be disabled by a MUTE signal (coincidence).


TDA4555 Multistandard decoder.


GENERAL DESCRIPTION
The TDA4555 and TDA4556 are monolithic integrated
multistandard colour decoders for the PAL, SECAM,
NTSC 3,58 MHz and NTSC 4,43 MHz standards. The
difference between the TDA4555 and TDA4556 is the
polarity of the colour difference output signals (B-Y)
and (R-Y).
Features
Chrominance part
· Gain controlled chrominance amplifier for PAL, SECAM
and NTSC
· ACC rectifier circuits (PAL/NTSC, SECAM)
· Burst blanking (PAL) in front of 64 ms glass delay line
· Chrominance output stage for driving the 64 ms glass
delay line (PAL, SECAM)
· Limiter stages for direct and delayed SECAM signal
· SECAM permutator
Demodulator part
· Flyback blanking incorporated in the two synchronous
demodulators (PAL, NTSC)
· PAL switch
· Internal PAL matrix
· Two quadrature demodulators with external reference
tuned circuits (SECAM)
· Internal filtering of residual carrier
· De-emphasis (SECAM)
· Insertion of reference voltages as achromatic value
(SECAM) in the (B-Y) and (R-Y) colour difference output
stages (blanking)
Identification part
· Automatic standard recognition by sequential inquiry
· Delay for colour-on and scanning-on
· Reliable SECAM identification by PAL priority circuit
· Forced switch-on of a standard
· Four switching voltages for chrominance filters, traps
and crystals
· Two identification circuits for PAL/SECAM (H/2) and
NTSC
· PAL/SECAM flip-flop
· SECAM identification mode switch (horizontal, vertical
or combined horizontal and vertical)
· Crystal oscillator with divider stages and PLL circuitry
(PAL, NTSC) for double colour subcarrier frequency
· HUE control (NTSC)
· Service switch.



TDA4560 Colour transient improvement circuit


GENERAL DESCRIPTION
The TDA4560 is a monolithic integrated circuit for colour transient improvement (CTI) and luminance delay line in gyrator
technique in colour television receivers.
Features
· Colour transient improvement for colour difference signals (R-Y) and (B-Y) with transient detecting-, storage- and
switching stages resulting in high transients of colour difference output signals
· A luminance signal path (Y) which substitutes the conventional Y-delay coil with an integrated Y-delay line
· Switchable delay time from 720 ns to 1035 ns in steps of 45 ns
· Output for the option of velocity modulation


FUNCTIONAL DESCRIPTION
The IC consists of two colour difference channels (B-Y) and (R-Y) and a luminance signal path (Y) as shown in Fig.1.
Colour difference channels
The (B-Y) and (R-Y) colour difference channels consist of a buffer amplifier at the input, a switching stage and an output
amplifier. The switching stages, which are controlled by transient detecting stages (differentiators), switch to a value that
has been stored at the beginning of the transients. The differentiating stages get their signal direct from the colour
difference detecting signal (pins 1 and 2). Two parallel storage stages are incorporated in which the colour difference
signals are stored during the transient time of the signal. After a time of about 600 ns they are switched immediately
(transient time of 150 ns) to the outputs. The colour difference channels are not attenuated.
Y-signal path
The Y-signal input (pin 17) is capacitively coupled to an input clamping circuit. Gyrator delay cells provide a maximum
delay of 1035 ns including an additional delay of 45 ns via the fine adjustment switch (S1) at pin 13. Three delay cells
are switched with two interstage switches dependent on the voltage at pin 15. Thus three switchable delay times of
90 ns, 180 ns or 270 ns less than the maximum delay time are available. A tuning compensation circuit ensures accuracy
of delay time despite process tolerances. The Y-signal path has a 7 dB attenuation as a normal Y-delay coil and can
replace this completely. The output is fed to pin 12 via a buffer amplifier. An additional output stage provides a signal of
90 ns less delay at pin 11 for the option of velocity modulation.




TDA4443 MULTISTANDARD VIDEO IF AMPLIFIERDESCRIPTION
The TDA4443 is a Video IF amplifier with standard
switch for multistandard colour or monochromeTV
sets, and VTR’s.

SWITCHING OFF THE IF AMPLIFIER WHEN
OPERATING IN VTR MODE .DEMODULATION OF NEGATIVE OR POSITIVE
IF SIGNALS. THE OUTPUT REMAINS
ON THE SAME POLARITY IN EVERY CASE .IF AGC AUTOMATICALLY ADJUSTED TO
THE ACTUALSTANDARD .TWO AGC POSSIBILITIES FOR B/G MODE :
1. GATED AGC
2. UNGATED AGC ON SYNC. LEVEL AND
CONTROLLED DISCHARGE DEPENDENT
ON THE AVERAGE SIGNAL LEVEL FOR VTR
AND PERI TV APPLICATIONS
FOR STANDARD L : FAST AGC ON PEAK
WHITE BY CONTROLLED DISCHARGE .POSITIVE OR NEGATIVE GATING PULSE .EXTREMELY HIGH INPUT SENSITIVITY .LOW DIFFERENTIAL DISTORTION .CONSTANT INPUT IMPEDANCE .VERY HIGH SUPPLY VOLTAGE REJECTION .FEW EXTERNAL COMPONENTS .LOW IMPEDANCE VIDEO OUTPUT .SMALL TOLERANCES OF THE FIXED VIDEO
SIGNALAMPLITUDE .ADJUSTABLE, DELAYED AGC FOR PNP
TUNERS.

GENERAL DESCRIPTION
This video IF processing circuit integrates the following
functional blocks : .Three symmetrical, very stable, gain controlled
wideband amplifier stages - without feedback
by a quasi-galvanic coupling. .Demodulator controlled by the picture carrier .Video output amplifier with high supply voltage
rejection .Polarity switch for the video output signal .AGC on peak white level .GatedAGC .Discharge control .Delayed tuner AGC .At VTR Reading mode the video output signal
is at ultra white level.



TDA4445A SOUND IF AMPLIFIER


.QUADRATURE INTERCARRIER DEMODULATOR
.VERY HIGH INPUT SENSITIVITY .GOODSIGNALTO NOISE RATIO .FAST AVERAGINGAGC .IF AMPLIFIER CAN BE SWITCHED OFF FOR
VTR MODE .GOODAM SUPPRESSION .OUTPUT SIGNAL STABILIZED AGAINST
SUPPLY VOLTAGE VARIATIONS .VERY FEW EXTERNAL COMPONENTS
DESCRIPTION
TDA4445A:
Sound IF amplifier, with FM processing for quasi
parallel sound system.
TDA4445B:
Sound IF amplifier, with FM processing and AM
demodulator, for multi-standard sound TV appliances.
TDA4445Badditionnal :
Bistandard applications (B/G and L)
No adjustment of the AM demodulator
Low AMdistortion.


GENERAL DESCRIPTION
This circuit includes the following functions : .Three symmetrical and gain controlled wide
band amplifier stages, which are extremely stable
by quasiDC coupling without feedback. .Averaging AGC with discharge control circuit .AGC voltage generator
Quasi parallel sound operation : .High phase accuracy of the carrier signal processing,
independentfrom AM .Linear quadrature demodulator .Sound-IF-amplifier stage with impedance converter
AM-Demodulation (only TDA4445B) : .Carrier controlled demodulator .Audio frequency stage with impedance converter
.Averaging low passAGC.



FINLUX TYPE 153 1532 28  CHASSIS 1000 Description Of The TMS7000/TMS7020/TMS7040/TMS70120/TMS7001/TMS7041

The TMS70X0 devices (TMS7000, TMS7020, TMS7040, and TMS70120) are single chip
8-bit microcomputers containing a CPU, timer, lIO, RAM, and various amounts of on-chip
ROM. The TMS7020 contains the CPU, RAM, timer, and l/O on-chip, and also provides 2K
bytes of on-chip ROM. The TMS7040 offers the same features as the TMS7020 and has an
increased on-chip ROM size of 4K bytes. The TMS7020 offers the same features as the
general family and efficiently handles large programs with 12K bytes of on-chip ROM. The
TMS7000 family member contains the same features of the TMS7020 except itcontains no
on-chip ROM.

The TMS70X1 devices (TMS7001 and TMS7041) contain a flexible on-chip serial port in
addition the CPU, timer, I/0, and on-chip RAM and ROM. The TMS7041 contains 4K bytes of
on-chip ROM, while the TMS7001 has no on-chip ROM.
Each member in the TMS70X0 and TMS70X1 families have 128 bytes of on-chip RAM, and all
have the capability through memory expansion modes, to access up to 64K bytes of address
space. For additional information on the TMS7000 family architecture, refer to Section 2.

Key Features:
Microprogrammable instruction set
Strip Chip Architecture Topology lSCAT) for rapid family expansion
Register-to-register architecture
Family members with 2K, 4K, and 12K bytes of on-chip ROM and ROMless versions
On-chip 8-bit timer/event counter with 5-bit prescale:
— Internal interrupt with automatic reload
— Capture latch
— Second 8-bit timer/event counter with 5-bit prescale and cascade capabilit
(TMS7001 and TMS7041 onlyl
Flexible on-chip serial port (TMS7001 and TMS7041 only)
- Fully software programmable
— Internal or external baud rate generator
— Separate baud rate timer usable as a third timer
— Asynchronous. isosynchronous, or serial modes
— Two multiprocessor communication formats
128-byte RAM register file
Full-feature datalprogram stack
32 TTL-compatible I/O pins:
— 16 bi-directional pins (22 bi-directional pins on TMS7001 and TMS7041)
— 8 output pins
— 8 high-impedance input pins (2 input pins on TMS7001 and TMS7041l
Memory-mapped ports for easy addressing
256-byte peripheral file
Memory expansion capability:
64K byte address space



TDA2541 IF AMPLIFIER WITH DEMODULATOR AND AFC
DESCRIPTION
The TDA2540 and 2541 are IF amplifier and A.M.
demodulator circuits for colour and black and white
televisionreceiversusingPNPorNPNtuners. They
are intended for reception of negative or positive
modulation CCIR standard.
They incorporate the following functions : .Gain controlled amplifier .Synchronous demodulator .White spot inverter .Video preamplifier with noise protection .Switchable AFC .AGC with noise gating .Tuner AGC output (NPN tuner for 2540)-(PNP
tuner for 2541) .VCR switch for video output inhibition (VCR
play back).




 
TDA2578A SYNCHRONIZATION CIRCUITWITH VERTICAL OSCILLATOR AND DRIVER STAGES
GENERAL DESCRIPTION
The TDA2578A separates the.verticaI and horizontal sync pulses from the composite TV video signal
and uses them to synchronize horizontal and vertical oscillators.
Features
O Horizontal sync separator and noise inverter
I Horizontal oscillator
0 Horizontal output stage
O Horizontal phase detector (sync to oscillator)
0 Time constant switch for phase detector (fast time constant during catching)
0 Slow time constant for noise only conditions
0 Time constant externally switchable (e.g. fast for VCR)
0 Inhibit of horizontal phase detector and video transmitter identification circuit during vertical
oscillator flyback
O Second phase detector ((p2) for storage compensation of horizontal deflection stage
I Sandcastle pulse generator (3~levels)
0 Video transmitter identification circuit
I Stabilizer and supply circuit for starting the horizontal oscillator and output stage directly from the
mains rectifier
0 Duty factor of horizontal output pulse is 50% when flyback pulse is absent
O Vertical sync separator
0 Bandgap 6,5 V reference voltage for vertical oscillator and comparator
0 Synchronized vertical oscillator/sawtooth generator
(synchronization inhibited when no video transmitter is detected)
0 Internal circuit for 6% parabolic pre-correction of the oscillator/sawtooth generator. Comparator
supplied with pre-corrected sawtooth and external feedback input
O Vertical driver stage
I Vertical blanking pulse generator
O 50/60 Hz detector
0 50/60 Hz identification output
I Automatic amplitude adjustment for 60 Hz
0 Automatic adjustment of blanking pulse duration
(50 Hz: 21 lines; 60 Hz:17Iines)
O Vertical guard curcuit
QUICK REFERENCE DATA
_i_i____.
Supply
Minimum current required to start horizontal
oscillator and output stage (pin 16) I15 > 4,5 mA
Main supply voltage (pin 10) Vp = V10_9 typ. I2 V
Supply current lp = I19 typ. 55 mA
Input signals
Sync pulse input voltage (peak-to-peak value; negative-going) V5_9(p_p) 0,15 to I V
Output signals
Horizontal output pulse (open collector) at I11 = 40 mA V11_9 < 0,5 V
Vertical output pulse (emitter-follower) at I1 = I0 mA V1_9 > 4 V

APPLICATION INFORMATION
The TDA2578A generates the signal for driving the horizontal deflection output circuit. lt also contains
a synchronized vertical sawtooth generator for direct drive of the vertical deflection output stage.
The horizontal oscillator and output stage can start operating on a very low supply current (I16 > 4,5 mA),
which can be taken directly from the mains rectifier. Therefore, it is possible to derive the main supply
(pin 10) from the horizontal deflection output stage. The duty factor of the horizontal output signal
is about 65% during the starting-up procedure. After starting-up, the second phase detector (tp2) is
activated to control the timing of the positive-going edge of the horizontal output signal.
A bandgap reference voltage (6,5 V) is provided for supply and reference of the vertical oscillator and
comparator stage. *
The slicing level of the horizontal sync separator is independent of the amplitude of the sync pulse at
the input. The resistor between pins 6 and 7 determines its value. A 4,7 kS2 resistor gives a slicing level
at the middle of the sync pulse. The nominal top sync level at the input is 3,1 V. The amplitude
selective noise inverter is activated at a level of 0,7 V.
Good stability is obtained by means of the two control loops. In the first loop, the phase of the
horizontal sync signal is compared with a waveform of which the rising edge refers to the top of the
horizontal oscillator signal. ln the second loop, the phase of the flyback pulse is compared with
another reference waveform, the timing of which is such that the top of the flyback pulse is situated
symmetrically on the horizontal blanking internal of the video signal. Therefore the first loop can be
designed for a good noise immunity, whereas the second loop can be as fast as desired for compensation
of switch-off delays in the horizontal output stage.
The first phase detector is gated with a pulse derived from the horizontal oscillator signal. This gating
(slow time constant) is switched off during catching. Also, the output current of the phase detector
is increased fivefold, during the catching time and VCR conditions (fast time constant). The first phase
detector is inhibited during the retrace time of the vertical oscillator.
The in-sync, out-of-sync or no video condition is detected by the video transmitter identification/coin-
cidence detector circuit (pin 18). The voltage on pin 18 defines the time constant and gating of the
first phase detector. The relationship between this voltage and the various switching levels is shown in
Fig. 3. The complete survey of the switching actions is given in Table 1.
Table 1 Switching levels at pin 18. ' -
voltage at first phase detector np1 I mute output receiving conditions
E
7,5 V X X X video signal detected
7,5 to 3,5 V X X X video signal detected
3,5 to 1,2 V X X X video signal detected
1,2 to 0,1 V X X X noise only
0,1 to 1,7 V X * X * X new video signal detected
1,7 to 5,0 V X X X horizontal oscillator locked
VCR playback with mute function
5,0 to 7,5 V X X X horizontal oscillator locked
8,7 V X X X VCR playback without mute function
Where: * = 3 vertical periods.

The stability of displayed video information (e.g. channel number), during noise only conditions, is
improved by the first phase detector time constant being set to slow.
The average voltage level of the video input on pin 5 during noise only conditions should not exceed
5,5 V otherwise the time constant switch may be set to fast due to the average voltage level on pin I8
dropping below 0,1 V. When the voltage on pin 18 drops below I00 mV a counter is activated which
sets the time constant switch to fast, and not gated for 3 vertical periods. This condition occurs when
a new video signal is present at pin 5. When the horizontal oscillator is locked the voltage on pin I8
increases. Nominally a level of 5 V is reached within 15 ms (I vertical period). The mute switching
level of 1,2 V is reached within 5 ms (C18 = 47 nF). If the video transmitter identification circuit is
required to operate under VCR playback conditions the first phase detector can be set to fast by
connecting a resistor of I80 kS2 between pin I8 and ground (see Fig. 7).
The supply for the horizontal oscillator (pin 15) and horizontal output stage (pin II) is derived from
the voltage at pin 16 during the start condition. The horizontal output signal starts at a nominal
supply current into pin 16 of 4,2 mA, which will result in a supply voltage of about 5,5 V (for
guaranteed operation of all devices I16 > 4,5 mA). lt is possible that the main supply voltage at pin 10
is O V during starting, so the main supply of the lC can be taken from the horizontal deflection output
stage. The start of the other lC functions depends on the value of the main supply voltage at pin IO.
At 5,5 V all IC functions start operating except the second phase detector (oscillator to flyback pulse).
The output voltage of the second phase detector at pin 14 is clamped by means of an internally
loaded n-p-n emitter follower. This ensures that the duty factor of the horizontal output signal (pin 11)
remains at about 65%. The second phase detector will close if the supply voltage at pin 10 reaches
8,8 V. At this value the supply current for the horizontal oscillator and output stage is delivered by
pin IO, which also causes the voltage at pin 16 to change to a stabilized 8,7 V. This change switches
off the n-p-n emitter follower at pin 14 and activates the second phase detector. The supply voltage
for the horizontal oscillator will, however, still be referred to the stabilized voltage at pin I6, and the
duty factor of the output signal at pin I2 is at the value required by the delay at the horizontal
deflection stage. Thus switch-off delays in the horizontal output stage are compensated. When no
horizontal flyback signal is detected the duty factor of the horizontal output signal is 50%.
Horizontal picture shift is possible by externally charging or discharging the 47 nF capacitor connected
to pin I4.
The IC also contains a synchronized vertical oscillator/sawtooth generator. The oscillator signal is
connected to the internal comparator (the other side of which is connected to pin 2), via an inverter
and amplitude divider stage. The output of the comparator drives an emitter-follower output stage at
pin I. For a linear sawtooth in the oscillator, the load resistor at pin 3 should be connected to a voltage
source of 26 V or higher. The sawtooth amplitude is not influenced by the main supply at pin 10.
The feedback signal is applied to pin 2 and compared to the sawtooth signal at pin 3. For an economical
feedback circuit with less picture bounce the sawtooth signal is internally pre-corrected by 6% (convex)
referred to pin 2. The linearity of the vertical deflection current depends upon the oscillator signal at
pin 3 and the feedback signal at pin 2.
Synchronization of the vertical oscillator is inhibited when the mute output is present at pin 13.
To minimize the influence of the horizontal part on the vertical part a 6,7 V bandgap reference source
is provided for supply and reference of the vertical oscillator and comparator.
The sandcastle pulse, generated at pin 17, has three different voltage levels. The highest level (ll V) can
be used for burst gating and black level clamping. The second level (4,6 V) is obtained from the
horizontal flyback pulse at pin 12 and used for horizontal blanking. The third level (2,5 V) is used for
vertical blanking and is derived by counting the horizontal frequency pulses. For 50 Hz the blanking
pulse duration is 21 lines and for 60 Hz it is 17 lines. The blanking pulse duration and sawtooth
amplitude is automatically adjusted via the 50/60 Hz detector.


TDA3654 TDA3654Q Vertical deflection and guard circuit (110°)


GENERAL DESCRIPTION
The TDA3654 is a full performance vertical deflection output circuit for direct drive of the deflection coils and can be used
for a wide range of 90° and 110° deflection systems.
A guard circuit is provided which blanks the picture tube screen in the absence of deflection current.
Features
· Direct drive to the deflection coils
· 90° and 110° deflection system
· Internal blanking guard circuit
· Internal voltage stabilizer.

FUNCTIONAL DESCRIPTION
Output stage and protection circuits
The output stage consists of two Darlington configurations in class B arrangement.
Each output transistor can deliver 1,5 A maximum and the VCEO is 60 V.
Protection of the output stage is such that the operation of the transistors remains well within the SOAR area in all
circumstances at the output pin, (pin 5). This is obtained by the cooperation of the thermal protection circuit, the
current-voltage detector and the short circuit protection.
Special measures in the internal circuit layout give the output transistors extra solidity, this is illustrated in Fig.5 where
typical SOAR curves of the lower output transistor are given. The same curves also apply for the upper output device.
The supply for the output stage is fed to pin 6 and the output stage ground is connected to pin 4.
Driver and switching circuit
Pin 1 is the input for the driver of the output stage. The signal at pin 1 is also applied to pin 3 which is the input of a
switching circuit (pin 1 and 3 are connected via external resistors).
This switching circuit rapidly turns off the lower output stage when the flyback starts and it, therefore, allows a quick start
of the flyback generator. The maximum required input signal for the maximum output current peak-to-peak value of 3 A
is only 3 V, the sum of the currents in pins 1 and 3 is then maximum 1 mA.
Flyback generator
During scan, the capacitor between pins 6 and 8 is charged to a level which is dependent on the value of the resistor at
pin 8 When the flyback starts and the voltage at the output pin (pin 5) exceeds the supply voltage, the flyback generator is
activated.

The supply voltage is then connected in series, via pin 8, with the voltage across the capacitor during the flyback period.
This implies that during scan the supply voltage can be reduced to the required scan voltage plus saturation voltage of
the output transistors.
The amplitude of the flyback voltage can be chosen by changing the value of the external resistor at pin 8.
It should be noted that the application is chosen such that the lowest voltage at pin 8 is > 1,5 V, during normal operation.
Guard circuit
When there is no deflection current, for any reason, the voltage at pin 8 becomes less than 1 V, the guard circuit will
produce a d.c. voltage at pin 7. This voltage can be used to blank the picture tube, so that the screen will not burn in.
Voltage stabilizer
The internal voltage stabilizer provides a stabilized supply of 6 V to drive the output stage, so the drive current is not
affected by supply voltage variations.

FINLUX TYPE 153 1532 28 CHASSIS 1000 CRT TUBE PHILIPS A59EAK00X01 45AX SYSTEM.

INTRODUCTION:
This type the 45AX FST TUBE BY PHILIPS WAS WIDELY USED AROUND THE WORLD and fabricated form more than 22 YEARS.


Picture display system including a deflection unit with a double saddle coil system
PHILIPS 45AX SYSTEM.

 CRT TUBE PHILIPS  A59EAK(xx)X(xx)  FLAT SQUARE Hi-Bri COLOUR PICTURE TUBE 45AX SYSTEM
• Flat and square screen
• 110° deflection
• In-line, hi-bi potential A RT* gun with quadrupole cathode lens
• 29, 1 mm neck diameter
• Mask with corner suspension
• Hi-Bri technology
• Pigmented phosphors
• Quick-heating low-power cathodes
• Soft flash
• Slotted shadow mask optimized for minimum moire at 625 lines systems
• Internal magnetic shield
• Internal multipole
• Reinforced envelope for push-through mounting
• Anti-crackle coating



GENERAL OPERATIONAL RECOMMENDATIONS

INTRODUCTION
Equipment design should be based on the characteristics as stated in the data sheets. Where deviations from these general recommendations are permissible or necessary, statements to that effect will be made. If applications are considered which are not referred to in the data sheets of the relevant tube type, extra care should be taken with circuit design to prevent the tube being overloaded due to unfavourable operating conditions.

SPREAD IN TUBE CHARACTERISTICS
The spread in tube characteristics is the difference between maximum and minimum values. Values not qualified as maximum or minimum are nominal ones. It is evident that average or nominal values, as well as spread figures, may differ according to the number of tubes of a certain type that are being checked. No guarantee is given for values of characteristics in settings substantially differing from those specified in the data sheets.

SPREAD AND VARIATION IN OPERATING CONDITIONS
The operating conditions of a tube are subject to spread and/or variation. Spread in an operating condition is a permanent deviation from an average condition due to, e.g.. component value deviations. The average condition is found from such a number individual cases taken at random that an increase of the number will have a negligible influence. Variation in an operating condition is non-permanent (occurs as a function of time). e.g .. due to supply voltage fluctuations. The average value is calculated over a period such that a prolongation of that period will have negligible influence.

LIMITING VALUES
Limiting values are in accordance with the applicable rating system as defined by IEC publication 134. Reference may be made to one of the following 3 rating systems. Absolute maximum rating system. Absolute maximum ratings are limiting values of operating and environmental conditions applicable to any electronic device of a specified type as defined by its published data, and should not be exceeded under the worst probable conditions. These values are chosen by the device manufacturer to provide acceptable serviceability of the device, taking no responsibility for equipment variations, environmental variations, and the effects of changes in operating conditions due to variations in the characteristics of the device under consideration and of all other electronic devices in the equipment. The equipment manufacturer should design so that, initially and throughout life, no absolute maximum value for the intended service is exceeded with any device under the worst probable operating condit- ions with respect to
supply voltage variation, equipment components spread and variation, equipment control adjustment, load variations, signal variation, environmental .conditions, and spread or variations in characteristics of the device under considerations and of all other electronic devices in the equipment.

Design-maximum rating system.
Design-maximum ratings are limiting values of operating and environ- mental conditions applicable to a bogey electronic device* of a specified type as defined by its pub- lished data, and should not be exceeded under the worst probable conditions. These values are chosen by the device manufacturer to provide acceptable serviceability of the device, taking responsibility for the effects of changes in operating conditions due to variations in the charac- teristics of the electronic device under consideration. The equipment manufacturer should design so that, initially and thoughout life, no design-maximum value for the intended service is exceeqed with a bogey device under the worst probable operating conditions with respect to supply-voltage variation, equipment component variation, variation in char- acteristics of all other devices in the equipment, equipment control adjustment, load variation, signal variation and environmental conditions.

Design-centre rating system.
Design-centre ratings are limiting values of operating and environmental conditions applicable to a bogey electronic device* of a specified type as defined by its published data, and should not be exceeded under average conditions. These values are chosen by the device manufacturer to provide acceptable serviceability of the device in average applications, taking responsibility for normal changes in operating conditions due to rated supply-voltage variation, equipment component spread and variation, equipment control adjustment, load variation, signal variation, environmental conditions, and variations or spread in the characteristics of all electronic devices. The equipment manufacturer should design so that, initially, no design-centre value for the intended service is exceeded with a bogey electronic device* in equipment operating at the stated normal supply voltage.

If the tube data specify limiting values according to more than one rating system the circuit has to be
designed so that none of these limiting values is exceeded under the relevant conditions.
In addition to the limiting values given in the individual data sheets the directives in the following
paragraphs should be observed.

HEATER SUPPLY
For maximum cathode life and optimum performance it is recommended that the heater supply be designed at the nominal heater voltage at zero beam current. Any deviation from this heater voltage has a detrimental effect on tube performance and life, and should therefore be kept to a minimum. Jn any case the deviations of the heater voltage must not exceed+ 5% and -10% from the nominal value at zero beam current. Such deviations may be caused by:

• mains voltage fluctuations;
• spread in the characteristics of components such as transformers, resistors, capacitors, etc.;
• spread in circuit adjustments;
• operational variations.

• A bogey tube is a tube whose characteristics have the published nominal values for the type. A bogey tube for any particular application can be obtained by considering only those characteristics which are directly related to the application.

CATHODE TO HEATER VOLTAGE
The voltage between cathode and heater should be as low as possible and never exceed the limiting values given in the data sheets of the individual tubes. The limiting values relate to that side of the heater where the voltage between cathode and heater is greatest. The voltage between cathode and heater may be d.c., a.c., or a combination of both. Unless otherwise stated, the maximum values quoted indicate the maximum permissible d.c. voltage. If a combination of d.c. and a.c. voltages is applied, the peak value may be twice the rated Vkf; however, unless otherwise stated, this peak value shall never exceed 315 V. Unless otherwise stated, the Vkf max. holds for both polarities of the voltage; however, a positive cathode is usually the most favourable in view of insulation during life. A d.c. connection should always be present betweeh heater and cathode. Unless otherwise specified the maximum resistance should not exceed 1 M.Q; the maximum impedance at mains frequency shou Id be less than 100 k.OHM.

INTERMEDIATE ELECTRODES (between cathode and anode)
In no circumstances should the tube be operated without a d.c. connection between each electrode and the cathode. The total effective impedance between each electrode and the cathode shou Id never exceed the published maximum value. However, no electrode should be connected directly to a high energy source. When such a connection is required, it should be made via a series resistor of not less
than 1 k.OHM.

CUT-OFF VOLTAGE
Curves showing the limits of the cut-off voltage as a function of grid 2 voltage are generally included in the data. The brightness control should be so dimensioned that it can handle any tube within the limits shown, at the appropriate grid 2 voltage. The published limits are determined at an ambient illumination level of 10 lux. Because the brightness of a spot is in general greater than that of a raster of the same current, the cut-off voltage determined with the aid of a focused spot will be more negative by about 5 Vas compared with that of a focused
raster.

LUMINESCENT SCREEN
To prevent permanent screen damage, care should be taken: - not to operate the tube with a stationary picture at high beam currents for extended periods; - not to operate the tube with a stationary or slowly moving spot except at extremely low beam currents; - if no e.h.t. bleeder is used, to choose the time constants of the cathode, grid 1, grid 2, and deflection circuits, such that sufficient beam current is maintained to discharge the e.h.t. capacitance before deflection has ceased after equipment has been switched off.

EXTERNAL CONDUCTIVE COATING
The external conductive coating must be connected to the chassis. The capacitance of this coating to the final accelerating electrode may be used to provide smoothing for the e.h.t. supply. The coating is not a perfect conductor and in order to reduce electromagnetic radiation caused by the line time base and the picture content it may be necessary to make multiple connections to the coating.
See also 'Flashover'.

METAL RIMBAND
An appreciable capacitance exists between the metal rimband and the internal conductive coating of the tube; its value is quoted in the individual data sheets.To avoid electric shock, a d.c. connection should be provided between the metal band and the external conductive coating. In receivers where the chassis ,can be connected directly to the mains there is a risk of electric shock if access is made to the metal band. To reduce the shock to the safe limit, it is suggested that a 2 Mil resistor capable of handling the peak voltages be inserted between the metal band and the point of contact with the external con- ductive coating. This safety arrangement will provide the necessary insulation from the mains but in the event of flashover high voltages will be induced on the metal band. It is therefore recommended that the 2 Mil resistor be bypassed by a 4, 7 n F capacitor capable of withstanding the peak voltage determined by the voltage divider formed by this capacitor and the capacitance of the metal rimband
to the internal conductive coating, and the anode voltage. The 4, 7 n F capacitor also serves to improve e.h.t. smoothing by addingthe rimband capacitance to the capacitance of the outer conductive coating.

FLASHOVER
High electric field strengths are present between the gun electrodes of picture tubes. Voltages between gun electrodes may reach values of 20 kV over approx. 1 mm. Although the utmost precautions are taken in the design and manufacture of the tubes, there is always a chance that flashover will occur. The resulting transient currents and voltages may be of sufficient magnitude to cause damage to the tube itself and to various components on the chassis. Arcing terminates when the e.h.t. capacitor is discharged. Therefore it is of vital importance to provide protective circuits with spark gaps and series resistors, which should be connected according to Fig. 1. No other connections between the outer conductive coating and the chassis are permissible. As our picture tubes are manufactured in Soft-Flash technology, the peak discharge currents are limited to approx. 60 A, offering higher set reliability, optimum circuit protection and component savings (see also Technical Note 039). However this limited value of
60 A is still too high for the circuitry which is directly connected to the tube socket. Therefore Soft-Flash picture tubes should also be provided with spark gaps.

IMPLOSION PROTECTION
All picture tubes employ integral implosion protection and must be replaced with a tube of the same type number or recommended replacement to assure continued safety.

HANDLING
Although all picture tubes are provided with integral implosion protection, which meets the intrinsic protection requirements stipulated in the relevant part of IEC 65, care should be taken not to scratch or knock any part of the tube. The tube assembly should never be handled by the neck, deflection unit or other neck components. A picture tube assembly can be lifted from the edge-down position by using the two upper mounting lugs. An alternative lifting method is firmly to press the hands against the vertical sides of the rimband. When placing a tube assembly face downwards ensure that the screen rests on a soft pad of suitable material, kept free from abrasive substances. When lifting from the face-down position the hand should be placed under the areas of the faceplate close to the mounting lugs at diagonally opposite corners of the faceplate.

When lifting from the face-up position the hands should be placed under the areas of the cone close
to the mounting lugs at diagonally opposite corners of the cone.

In all handling procedures prior to insertion in the receiver cabinet there is a risk of personal injury as a result of severe accidental damage to the tube. It is therefore recommended that protective clothing shou Id be worn, particularly eye shielding. When suspending the tube assembly from the mounting lugs ensure that a minimum of 2 are used; UNDER NO Cl RCUMSTANCES HANG THE TUBE ASSEMBLY FROM ONE LUG. If provided the slots in the rimband of colour picture tubes are used in the mounting of the degaussing coils. it is not recommended to suspend the tube assembly from one or more of these slots as permanent deformation to the rimband can occur. Remember when replacing or servicing the tube assembly that a residual electrical charge may be carried by the anode contact and also the external coating if not earthed. Before removing the tube assembly from the equipment, earth the external coating and short the anode contact to the coating.

PACKING
The packing provides protection against tube damage under normal conditions of shipment or handling. Observe any instructions given on the packing and handle accordingly. The tube should under no circumstances be subjected to accelerations greater than 350 m/s2.

MOUNTING
Unless otherwise specified on the data sheets for individual tubes there are no restrictions on the position of mounting. The tube socket should not be rigidly mounted but should have flexible leads and be allowed to move freely. It is very desirable that tubes should not be exposed to strong electrostatic and magnetic fields.

DIMENSIONS
In designing the equipment the tolerances given on the dimensional drawings should be considered. Under no circumstances should the equipment be designed around dimensions taken from individual tubes.

Abstract

Self-convergent picture display system with a color display tube and an electromagnetic deflection unit including a field deflection coil and a line deflection coil which are both of the saddle type and are wound directly on a support. The deflection unit includes a pair of magnetically permeable portions which are arranged symmetrically with respect to the plane of symmetry of the field deflection coil on either side of the tube axis. The magnetically permeable portion draws magnetic flux from the end of the yoke ring in order to extend the vertical deflection field. A self-convergent system can be realized with different screen formats by choosing different lengths of the magnetically permeable portions.

What is claimed is:

1. A picture display system including a colour display tube having a neck accommodating an electron gun assembly for generating three electron beams, and an electromagnetic deflection unit surrounding the paths of the electron beams which have left the electron assembly, said deflection unit comprising

a field deflection coil of the saddle type having a front and a rear end for deflecting electron beams generated in the display tube in a vertical direction;

a line deflection coil of the saddle type likewise having a front and a rear end for deflecting electron beams generated in the display tube in a horizontal direction, and a yoke ring of ferromagnetic material surrounding the two deflection coils and having front and rear end faces extending transversely to the tube axis, the electron beam traversing the coils in the direction from the rear to the front ends when the deflection unit is arranged on a display tube, characterized in that the deflection unit also has first and second magnetically permeable portions arranged symmetrically with respect to the plane of symmetry of the field deflection coil on either side of the tube axis, each magnetically permeble portion having a first end located opposite the rear end face of the yoke ring and a second end located at the neck of the display tube in the proximity of the location where the electron beams leave the electron gun assembly, the length of the first and second magnetically permeable portions and their distance to the yoke ring being dimensioned for providing a self-convergent picture display system.

2. A picture display system as claimed in claim 1 characterized in that regions of the rear end of the yoke ring located on either side of the plane of symmetry of the line deflection coil are left free by the rear end of the field deflection coil and in that the first ends of the magnetically permeable portions are located opposite said regions.

3. A picture display system as claimed in claim 1 characterized in that the field deflection coil and the line deflection coil are directly wound on a support.

4. Apparatus for adapting a self-convergent deflection unit of the type mountable on the neck of a display tube and including a saddle type field deflection coil screen end and a gun end extending away from said tube in a plane disposed at an angle to a tube axis, and a yoke ring having a screen end and a gun end, for use with display tubes having different screen formats comprising:

format adjustment means disposed adjacent to the gun end of the yoke ring for coupling flux from the yoke ring to the neck of the tube to supplement the field produced by the vertical deflection coil to uniformly increase the vertical deflection field to produce a raster having a different format from the raster produced by said deflection unit alone.

5. The apparatus of claim 4 wherein said field deflection coil is arranged symmetrically about a plane of symmetry passing through said neck and said format adjustment means comprises first and second magnetically permeable members arranged symmetrically about said plane of symmetry, each of said magnetically permeable members having a first end disposed adjacent the gun end of the yoke ring and a second end disposed adjacent the neck of the display tube.

6. The apparatus of claim 5 wherein each of said first and second magnetically permeablel members comprises a first end located opposite a gun end face of the yoke ring, and a second end located at the neck of the display tube adjacent the location where the electron beams leave the electron gun assembly.

7. The apparatus of claim 6 wherein said first end comprises a portion of said permeable member disposed parallel to the neck of the displaya tube and said second end comprises a portion of said magnetically permeable member located perpepndicular to the neck of the display tube.

8. The apparatus of claim 7 wherein said second endsn of said magnetically permeable members have inwardly extending arms subending a first angle.

9. The appaaratus of claim 8 wherein said angle is large so that the supplemental field has a positive sixpole component.

10. The apparatus of claim 8 wherein said angle is very small, so that said supplemental field has a dipole component and a negative sixpole component.

11. Apparatus for adapting a self-convergent deflection unit of the type used on the neck of a display tube having an electron gun disposed in a neck of said tube, said deflection unit including a field deflection coil of the saddle type having a rear end portion disposed at an angle to the axis of said tube, comprising means disposed adjacent to said neck between said electron gun and said deflection unit, and coupled to said deflection unit for changing the distance between the line and field deflection points for causing said deflection unit to produce a different screen format.

BACKGROUND OF THE INVENTION The invention relates to a picture display system including a colour display tube having a neck accommodating an electron gun assembly for generating three electron beams, and an electromagnetic deflection unit including a field deflection coil of the saddle type having a front and a rear end for deflecting electron beams generated in the display tube in a vertical direction and a line deflection coil of the saddle type likewise having a front and a rear end for deflecting electron beams generated in the display tube in a horizontal direction and yoke ring of ferromagnetic material surrounds the two deflection coils and has front and rear end faces extending transversely to the tube axis, the electron beam traversing the coils in the direction from the rear to the front ends when the deflection unit is arranged on a display tube. FOr some time a colour display tube has become the vogue in which three electron beams are used in one plane; the type of such a cathode ray tube is sometimes referred to as "in-line". In this case, for decreasing convergence errors of the electron beams, a deflection unit is used having a line deflection coil generating a horizontal deflection field of the pincushion type and a field deflection coil generating a vertical deflection field of the barrel-shaped type. Deflection units for in-line colour display tube systems can in principle be made to be entirely self-convergent, that is to say, in a design of the deflection unit which ensures convergence of the three electron beams on the axes, anisotropic y-astigmatism errors, if any, can simultaneously be made zero in the corners without this requiring extra correction means. While it would be interesting from a point of view of manufacture to have a deflection unit which is selfconvergent for a family of display tubes of the same deflection angle and neck diameter, but different screen formats, the problem exists, however, that a deflection unit of given main dimensions can only be used for display tubes of one screen format. This means that only one screen format can be found for a fixed maximum deflection angle in which aa given deflection unit is self-convergent without a compromise (for example, the use of extra correction means). The Netherlands Patent Specification 174 198 provides a solution to this problem which is based on the fact that, starting from field and line deflection coils having given main dimensions, selfconvergent deflection units for a family of display tubes having different screen formats can be assembled by modifying the effective lengths of the field and line deflection coils with respect to each other. This solution is based on the recognition that, if selfconvergence on the axes has been reached, the possibly remaining anisotropic y-astigmatism error (particularly the y-convergence error halfway the diagonals) mainly depends on the distance between the line deflection point and the field deflection point and to a much smaller extent on the main dimensions of the deflection coils used. If deflection units for different screen formats are to be produced while using deflection coils having the same main dimensions, the distance between the line and field deflection points may be used as a parameter to achieve self-convergence for a family of display tubes having different screen formats but the same maximum deflection angle. The variation in the distance between the line and field deflection points necessary for adaption to different screen formaats is achieved in the prior art by either decreasing or increasing the effective coil length of the line deflection coil or of the field deflection coil, or of both - but then in the opposite sense - with the maiin dimensions of the deflection coils remaining the same and with the dimensions of the yoke ring remaining the same, for example, by mechanically making the coil or coils on the rear side smaller and longer, respectively, by a few millimeters, or by positioning, with the coil length remaining the same, the coil window further or less far to the rear (so thata the turns on the rear side are more or less compressed). To achieve this, saddle-shaped line and field deflection coils of the shell type were used. These are coils having ends following the contour of the neck of the tube at least on the gun side. This is in contrast to the conventional saddle coils in which the gun-sided ends, likewise as the screen-sided ends, are flanged and extend transversely to the tube surface. When using saddle coils of the shell type it is possible for the field deflection coil (and hence the vertical deflection field) to extend further to the electron gun assembly than the line deflection coil, if the field design so requires. However, there are also deflection units with deflection coils of the conventional saddle type, which means that - as stated - they have front and rear ends located in planes extending at an angle (generally of 90.degree. ) to the tube axis. (A special type of such a deflection unit with conventional saddle coils is, for example, the deflection unit described in EP 102 658 with field and line deflection coils directly wound on a support). In this case it has until now been impossible to extend the vertical deflection field further to the electron gun assembly than the horizontal deflection field, because the field deflection coil is enclosed between the flanges of the line deflection coil.

SUMMARY OF THE INVENTION The deflection unit has first and second magnetically permeable portions arranged symmetrically with respect to the plane of symmetry of the field deflection coil on either side of the tube axis, each magnetically permeable portion having a first end located opposite the rear end face of othe yoke ring and a second end located at the neck of the display tube in the proximity of the location where the electron beams leave the electron gun assembly. The length of the first and second magnetically permeable portions and their distance to the yoke ring are dimensioned for providing a self-convergent picture display system. The invention is based on the recognition that the first ends of the magnetically permeable portions draw a field deflection flux flux which is taken up is adjusted by means of the distance between the first ends and the yoke ring, and the length of the magnetically permeable portions determines how far the vertical deflection field is extended to the rear. A practical embodiment of the picture display system according to the invention is characterized in that regions of the rear end of the yoke ring located on either side of the plane of symmetry of the line deflection coil are left free by the rear end of the field deflection coil and in that the first ends of the magnetically permeable portions are located opposite said regions. The invention can particularly be used to advanatage if the field deflection coil and the line deflection coil are directly wound on a support. The invention also relates to an electromagnetic deflection unit suitable for use in a picture display system as described hereinbefore. For use in a display tube having a larger screen format than the display tube for which it is designed, the invention provides the possibility of moving apart the deflection points of the horizontal deflection field and the vertical deflection field generated by a given deflection unit having saddle coils and of moving them towards each other for use in a display tube having a smaller screen format. The great advantage of the invention is that only a modification of the length of the magnetically permeable portions (providing or omitting them, respectively) is required to adapt a deflection unit to different screen formats of a display tube family.

CRT TUBE PHILIPS 45AX TECHNOLOGY Method of Production / manufacturing a color display CRT tube and color display tube manufactured according to said method.A ring is provided to correct the convergence, color purity and frame errors of a color display tube which ring is magnetized as a multipole and which is secured in or around the tube neck and around the paths of the electron beams.

The magnetization of such a ring can best be carried out by energizing a magnetization unit with a combination of direct currents thereby generating a multipole magnetic field and then effecting the magnetization by generating a decaying alternating magnetic field which preferably varies its direction continuously.

1. A method of manufacturing a color display tube in which magnetic poles are provided in or around the neck of said tube and around the paths of the electron beams, which poles generate a permanent static multipole magnetic field for the correction of errors in convergence, color purity and frame of the display tube, which magnetic poles are formed by the magnetisation of a configuration of magnetisable material provided around the paths of the electron beams, the method comprising energizing a magnetisation device with a combination of direct currents with which a static multipole magnetic field is generated, and superimposing a decaying alternating magnetic field over said static multipole magnetic field which initially drives said magnetisable material into saturation on either side of the hysteresis curve thereof, said decaying alternating magnetic field being generated by a decaying alternating current. 2. The method as claimed in claim 1, 6 or 7, wherein the decaying alternating magnetic field is generated by means of a separate system of coils in the magnetisation device. 3. The method as claimed in claim 2, wherein the decaying alternating magnetic field varies its direction continuously. 4. The method as claimed in claim 3 wherein the frequency of the decaying alternating current is approximately the standard line frequency. 5. A colour display tube manufactured by means of the method as claimed in claim 4. 6. The method as claimed in claim 1 which further comprises erasing any residual magnetism in said configuration, prior to said magnetisation, with an alternating magnetic field. 7. The method as claimed in claim 6 which further comprises correcting the errors in convergence, color purity and frame of the display picture with a combination of direct currents applied to said magnetisation device and then reversing said direct currents while increasing the magnitudes thereof and applying these adjusted direct currents to said magnetisation device for the magnetisation of said configuration.

Description:

BACKGROUND OF THE INVENTION
The invention relates to a method of manufacturing a color display tube in which magnetic poles are provided in or around the neck of the envelope and around the paths of the electron beams, which poles generate a permanent multipole magnetic field for the correction of the occurring errors in convergence, color purity and frame of the color display tube, which magnetic poles are formed by the magnetisation of a configuration of magnetisable material provided around the paths of the electron beams, which configuration is magnetized by energising a magnetising device with a combination of currents with which a static multipole magnetic field is generated.
The invention also relates to a color display tube manufactured according to said method.
In a color display tube of the "delta" type, three electron guns are accommodated in the neck of the tube in a triangular arrangement. The points of intersection of the axes of the guns with a plane perpendicular to the tube axis constitute the corner points of an equilateral triangle.
In a color display tube of the "in-line" type three electron guns are arranged in the tube neck in such manner that the axes of the three guns are situated mainly in one plane while the axis of the central electron gun coincides substantially with the axis of the display tube. The two outermost electron guns are situated symmetrically with respect to the central gun. As long as the electron beams generated by the electron guns are not deflected, the three electron beams, both in tubes of the "delta" type and of the "in-line" type, must coincide in the center of the display screen (static convergence). Because, however, as a result of defects in the manufacture of the display tube, for example, the electron guns are not sealed quite symmetrically with respect to the tube axis, deviations of the frame shape, the color purity and the static convergence occur. It should be possible to correct said deviations.

Such a color display tube of the "in-line" type in which this correction is possible, is disclosed in Netherlands Pat. application No. 7,503,830 laid open to public inspection. Said application describes a color display tube in which the deviations are corrected by the magnetisation of a ring of magnetisable material, as a result of which a static magnetic multipole is formed around the paths of the electron beams. Said ring is provided in or around the tube neck. In the method described in said patent application, the color display tube is actuated after which data, regarding the value and the direction of the convergence errors of the electron guns, are established, with reference to which the polarity and strength of the magnetic multipole necessary to correct the frame, color purity and convergence errors are determined. The magnetisation of the configuration, which may consist of a ring, a ribbon or a number of rods or blocks grouped around the electron paths, may be carried out in a number of manners. It is possible, for example, first to magnetise the configuration to full saturation, after which demagnetisation to the desired value is carried out with an opposite field. A disadvantage of this method is that, with a combination of, for example, a 2, 4, and 6-pole field, the polarity and strength of the demagnetisation vary greatly and frequently, dependent on the place on the ring, and hence also the polarity and strength of the full magnetisation used in this method. Moreover it appears that the required demagnetising field has no linear relationship with the required correction field. Due to this non-linearity it is not possible to use a combined 2, 4 and 6-pole field for the demagnetisation. It is impossible to successively carry out the 2, 4 and 6-pole magnetisation since, for each magnetisation, the ring has to be magnetised fully, which results in the preceding magnetisation being erased again. The possibility of successively magnetising various places on the ring is very complicated and is not readily possible if the ring is situated in the tube neck since the stray field of the field necessary for the magnetisation again demagnetizes, at least partly, the already magnetised places.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a method with which a combined multipole can be obtained by one total magnetisation.
According to the invention, a method, of the kind described in the first paragraph with which this is possible, is characterized in that the magnetisation is effected by means of a decaying alternating magnetic field which initially drives the magnetisable material on either side of the hysteresis curve into saturation. After the decay of the alternating magnetic field, a hard magnetisation remains in the material of the configuration which neutralizes the externally applied magnetic field and is, hence, directed oppositely thereto. After switching off the externally applied magnetic field, a magnetic multipole field remains as a result of the configuration magnetized as a multipole. The desired magnetisation may be determined in a number of manners. By observing and/or measuring the deviations in the frame shape, color purity and convergence, the desired multipole can be determined experimentally and the correction may be carried out by magnetisation of the configuration. If small deviations are then still found, the method is repeated once or several times with corrected currents. In this manner, by repeating the method according to the invention, it is possible to produce a complete correction of the errors in frame, color purity and convergence. Preceding the magnetisation, residual magnetism, if any, in the configuration is preferably erased by means of a magnetic field.
The method is preferably carried out by determining the required correction field prior to the magnetisation and, after the erasing of the residual magnetism, by correcting the errors in the convergence, the color purity and the frame of the displayed picture by means of a combination of currents through the magnetising device, after which the magnetisation is produced by reversing the direction of the combination of currents, increasing the current strength and simultaneously producing the said decaying alternating magnetic field.
The correction field, obtained with the magnetizing device and measured along the axis of the electron beams, is generally longer than the multipole correction field generated by the configuration. So the correction of the deviations will have to be carried out over a shorter distance along the axis of the tube, which is possible only with a stronger field. During the magnetisation, a combination of currents, which in strength and direction is in the proportion of m:1 to the combination of currents which is necessary to generate a correction multipole field with the device, where m is, for example, -3, should flow through the magnetisation device. The value of m depends on the ratio between the length of the correction multipole field, generated by the magnetizing device, to the effective field length of the magnetized configuration. This depends upon a number of factors, for example, the diameter of the neck, the kind of material, the shape and the place of the configuration, etc., and can be established experimentally. If it proves, upon checking, that the corrections with the magnetized configuration are too large or too small, the magnetisation process can be repeated with varied magnetisation currents.
The decaying alternating magnetic field can be generated by superimposing a decaying alternating current on the combination of currents through the magnetisation device (for example, a device as disclosed in Netherlands Pat. application No. 7,503,830 laid open to public inspection). The decaying alternating magnetic field is preferably generated in the magnetisation device by means of a separate system of coils. In order to obtain a substantially equal influence of all parts of the configuration by the decaying alternating field, it is recommendable not only to cause the alternating field to decay but also to cause it to vary its direction continuously. The system of coils therefore consists preferably of at least two coils and the decaying alternating currents through the coils are shifted in phase with respect to each other. Standard line frequency (50 or 60 Hz) has proven to give good results. The phase shift, when using coils or coil pairs, the axes of which enclose angles of 120° with each other, can simply be obtained from a three-phase line.
DESCRIPTION OF THE DRAWINGS
The invention will now be described in greater detail with reference to a drawing, in which
FIG. 1 is a diagrammatic sectional view of a known color display tube of the "in-line" type having an external static convergence unit,
FIG. 2 shows the pinion transmission used therein,
FIGS. 3 and 4 are two diagrammatic perpendicular cross-sectional views of the color display tube with a ring, which has not yet been magnetized, and in which the outermost electron beams do not converge satisfactorily,
FIGS. 5 and 6 are two diagrammatic perpendicular sectional views of a color display tube in which convergence by means of the magnetisation device has been obtained,
FIGS. 7 and 8 show the magnetisation of a ring arranged in the system of electron guns,
FIGS. 9 and 10 show two diagrammatic perpendicular sectional views of a color display tube with a magnetized ring with which the convergence error, as shown in FIG. 4, is removed,
FIGS. 11 and 12 show two types of devices suitable for magnetisation according to the invention, and
FIGS. 13 to 18 show parts of another type of magnetisation unit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a diagrammatic sectional view of a known color display tube of the "in-line" type. Three electron guns 5, 6 and 7, generating the electron beams 8, 9 and 10, respectively, are accommodated in the neck 4 of a glass envelope 1 which is composed of a display window 2, a funnel-shaped part 3 and a neck 4. The axes of the electron guns 5, 6 and 7 are situated in one plane, the plane of the drawing. The axis of the central electron gun 6 coincides substantially with the tube axis 11. The three electron guns are seated in a sleeve 16 which is situated coaxially in the neck 4. The display window 2 has on the inner surface thereof a large number of triplets of phosphor lines. Each triplet comprises a line of a phosphor luminescing green, a line of a phosphor luminescing blue, and a line of a phosphor luminescing red. All of the triplets together constitute a display screen 12. The phosphor lines are normal to the plane of the drawing. A shadow mask 12, in which a very large number of elongate apertures 14 are provided through which the electron beams 8, 9 and 10 pass, is arranged in front of the display screen 12. The electron beams 8, 9 and 10 are deflected in the horizontal direction (in the plane of the drawing) and in the vertical direction (at right angles thereto) by a system 15 of deflection coils. The three electron guns 5, 6 and 7 are assembled so that the axes thereof enclose a small angle with respect to each other. As a result of this, the generated electron beams 8, 9 and 10 pass through each of the apertures 14 at said angle, the so-called color selection angle, and each impinge only upon phosphor lines of one color.
A display tube has

a good static convergence if the three electron beams, when they are not being deflected, intersect each other substantially in the center of the display screen. It has been found, however, that the static convergence often is not good, no more than the frame shape and the color purity, which may be the result of an insufficiently accurate assembly of the guns, and/or sealing of the electron guns, in the tube neck. In order to produce the static convergence, so far, externally adjustable correction units have been added to the tube. They consist of a number of pairs of multipoles consisting of magnetic rings, for example four two-poles (two horizontal and two vertical), two four-poles and two six-poles. The rings of each pair are coupled together by means of a pinion transmission (see FIG. 2), with which the rings are rotatable with respect to each other to an equal extent. By rotating the rings with respect to each other and/or together, the strength and/or direction of the two-, four- or six-pole field is adjusted. It will be obvious that the control of a display tube with such a device is complicated and time-consuming. Moreover, such a correction unit is material-consuming since, for a combination of multipoles, at least eight rings are necessary which have to be provided around the neck so as to be rotatable with respect to each other.
In the Netherlands Pat. application No. 7,503,830, laid open to public inspection, the complicated correction unit has, therefore, been replaced by one or more magnetized rings, which rings are situated in or around the tube neck or in or around the electron guns.
However, it has proved difficult with the magnetising methods known so far to provide a combination of multipoles in the ring by magnetisation.
The method according to the invention provides a solution.
For clarity, identical components in the following figures will be referred to by the same reference numerals as in FIG. 1.
FIG. 3 is a diagrammatic sectional view of a display tube in which the electron beams do not converge in the horizontal direction. As is known, the outermost electron beams can be deflected more or less in the opposite direction by means of a four-pole, for example, towards the central beam or away therefrom. It is also possible to move the beams upwards and downwards. By means of a six-pole the beams can be deflected more or less in the same direction. For simplicity, the invention will be described with reference to a display tube which requires only a four-pole correction. The convergence errors in the horizontal direction of the electron beams 8 and 10 are in this case equally large but opposite.
FIG. 4 is a sectional view of FIG. 3. On the bottom of sleeve 16, a ring 18 is provided of an alloy of Fe, Co, V and Cr (known as Vicalloy) which can be readily magnetized. It will be obvious that the ring may alternatively be provided in other places around the guns or in or around the tube neck. Instead of a ring it is alternatively possible to use a ribbon or a configuration of rods or blocks of magnetisable material.
In FIG. 5 a device 19 for generating a controllable multipole magnetic field is provided around the neck 4 and the ring 18 according to the method of the invention. 2-, 4- or 6-poles and combinations thereof can be generated by means of the device 19. For the tube shown in FIG. 3, only a four-pole correction is necessary. The coils of the device 19, which device will be described in detail hereinafter, are in this case energized as four-poles until the point of intersection S of the three electron beams 8, 9 and 10, which in FIG. 3 was situated outside the tube 1, lies on the display screen 12. The current I through the coils of the device originates from a direct current source B which supplies a current -mI ₁ (m being an experimentally determined constant >1) to the coils via a current divider and commutator A. The current can be adjusted per coil so as to generate the desired multipole. In this phase of the method, an alternating current source C does not yet supply current (i=0).
FIG. 6 is a perpendicular sectional view of FIG. 5. The current I ₁ is a measure of the strength of the required correction field. The correction field of the multipole of the device 19 extends over a larger length of the electron paths than the magnetic field generated later by the magnetized ring. Therefore the field of the ring is to be m-times stronger.
FIG. 7 shows the step of the method in which the ring 18 is magnetized as a four-pole. As follows from the above, in this preferred embodiment of the method, the current through the coils of the device must be -mI ₁ during the magnetisation, so must traverse in the reverse direction and be m-times as large as the current through the coils during the correction. Moreover, the alternating current source C supplies a decaying alternating current (i=i ₁ >0) to the device 19, with which current the decaying alternating field is generated. When the alternating current is switched on, it must be so large that the ring 18 is fully magnetized on either side of the hysteresis curve. When the alternating field has decayed, the ring 18 is magnetized, in this case as a four-pole. It is, of course, alternatively possible to magnetise the ring 18 as a six-pole or as a two-pole or to provide combinations of said multipoles in the ring 18 and to correct therewith other convergence errors or color purity and frame errors. It is also possible to use said corrections in color display tubes of the "delta" type.
FIG. 9 shows the display tube 1 shown in FIG. 3, but in this case provided with a ring 18 magnetized according to the method of the invention as shown in FIGS. 5 and 7. The convergence correction takes place only by the magnetized ring 18 present in sleeve 16. The provision of the required multipole takes place at the display tube 1 factory and complicated adjustments and adjustable convergence units (FIG. 2) may be omitted.
FIG. 10 is a cross-sectional view perpendicular to FIG. 9. FIG. 11 shows a magnetisation device 19 comprising eight coils 20 with which the convergence (see FIG. 5) and the magnetisation (see FIG. 7) are carried out. For generating the decaying alternating magnetic field, two pairs of coils 21 and 22, extending in this case at right angles to each other, are incorporated in the device 19. The current i _a through the pair of coils 21 is shifted in phase through 90° with respect to the current i _b through the other pair of coils 22, so that the decaying alternating magnetic field changes its direction during the decay and is a field circulating through the ring 18. FIG. 12 shows a magnetisation device known from Netherlands Pat. application No. 7,503,830 laid open to public inspection. In this case, the decaying alternating current may be superimposed on the direct current through the coils 23 so that extra coils are not necessary in the device. The coils 23 are wound around a yoke 24.
The magnetisation device 19 may alternatively be composed of a combination of electrical conductors and coils, as is shown diagrammatically in FIGS. 13 to 18.
FIG. 13 is a sectional view of the neck 4 of a display tube 1 at the area of a ring 18 to be magnetised. A two-pole field for corrections in the horizontal direction is generated in this case by causing currents to flow through the conductors 25, 26, 27 and 28 in the direction as shown in the figure. Said conductors may be single wires or wire bundles forming part of one or more coils or turns, and extending parallel to the tube axis at the area of the ring 18.
FIG. 14 shows how, in an analogous manner, a four-pole field for corrections of the outermost beams 8 and 10 in the horizontal direction can be generated by electrical conductors 29, 30, 31 and 32. A four-pole field for corrections of the outermost beams 8 and 10 in the vertical direction is substantially the same. However, the system of conductors 29, 30, 31 and 32 is rotated through 45° with respect to the neck 4 and the axis of the tube 1.
FIG. 15 shows, in an analogous manner, a six-pole for corrections in the horizontal direction with conductors 33 to 38. By means of a combination of conductors (wires or wire bundles) with which 2-, 4- and 6-poles can be generated, all combinations of two-, four- and six-pole fields with the desired strength can be obtained by variations of the currents through said conductors 33 to 38.
The decaying alternating magnetic field in a magnetisation unit with conductors as shown in FIGS. 13, 14 and 15 can be obtained by means of coils positioned symmetrically around the neck 4 and the conductors as shown in FIGS. 16 and 17 or 18. By energizing the coils 39 and 40, shown in FIG. 16, with a decaying alternating current, a decaying alternating magnetic field is generated. A better influencing of the ring 18 by the decaying alternating field is obtained when a system of coils having coils 41 and 42 in FIG. 17 is provided which is rotated 90° with respect to the coils 39. In this case, 40 and the decaying alternating current through the coils 41 and 42 should then preferably be shifted 90° in phase with respect to the decaying alternating current through the coils 39 and 40.
It is alternatively possible to generate the decaying alternating magnetic field with one or more systems of coils as shown in FIG. 18. The coils 43, 44 and 45 are situated symmetrically around the tube axis and are energized with decaying alternating currents which are shifted 120° in phase with respect to each other (for example from a three-phase line).

CRT TUBE PHILIPS 45AX TECHNOLOGY Method of manufacturing a static convergence unit, and a color display tube comprising a convergence unit manufactured according to the method, PHILIPS 45AX INTERNAL STATIC CONVERGENCE SYSTEM Application technology:
IMACO RING (Integrated Magnetic Auto Converging )

The method according to the invention consists in the determination of data of the convergence errors of a color display tube, data being derived from the said determinations for determining the polarity and the intensity of magnetic poles of a structure. The structure thus obtained generates a static, permanent, multipole magnetic field adapted to the convergence errors occurring, so that the errors are connected.

What is claimed is: 1. A method of producing a magnetic convergence structure for the static convergence of electron beams which extend approximately in one plane in a neck of a color display tube of the kind in which the neck merges into a flared portion adjoined by a display screen, said method comprising
providing around the neck of the color display tube an auxiliary device for generating variable magnetic fields in the neck of the color display tube, activating the color display tube, adjusting the auxiliary device to produce a magnetic field for converging the electron beams, determining from data derived from the adjustment of the auxiliary device the extent and the direction of the convergence error of each electron beam, and using such data to determine the polarity and the intensity of magnetic poles of said magnetic convergence structure for generating a permanent multi-pole static magnetic field for the correction of the convergence errors occuring in the color display tube. 2. A method as claimed in claim 1, wherein the auxiliary device comprises an electromagnet convergence unit which comprises a number of coils, said generating step comprising passing electrical currents through said coils for generating a magnetic field required for the static convergence of the electron beams, and said determining step comprising using the values of the electrical currents for determining the permanent magnetic structure. 3. A method as claimed in claim 2, further comprising storing the data from the auxiliary device in a memory. 4. A method as claimed in claim 2, wherein said using step comprises controlling a magnetizing unit for magnetizing an annular magnetizable convergence structure. 5. A method as claimed in claim 2, further comprising converting the data into a code, and constructing said annular permanent magnetic convergence structure having a desired magnetic field strength from a set of previously magnetized structural parts. 6. A method as claimed in claim 1, further comprising forming the convergence structure from a magnetizable mass which is annularly arranged on at least one wall of the neck of the color display tube. 7. A method as claimed in claim 1, further comprising forming the convergence structure from a magnetizable ring which is arranged on the neck of the color display tube. 8. A method as claimed in claim 1, wherein the convergence structure comprises a non-magnetizable support and a number of permanent magnetic dipoles. 9. A method as claimed in claim 4, wherein said magnetizing step cofmprises polarizing the magnetizable material of the annular convergence structure at one location after the other by means of the magnetizing unit. 10. A method as claimed in claim 4, further comprising assemblying the auxiliary device and the magnetizing unit in one construction, and then enclosing a convergence structure to be magnetized with said magnetizing unit. 11. A method as claimed in claim 10, further comprising displacing said construction with respect to said tube after said determining step.

Description:

The invention relates to a method of manufacturing a magnetic convergence device for the static convergence of electron beams which extend approximately in one plane in a neck of a colour display tube, and to a colour display tube provided with a permanent magnetic device for the static convergence of electron beams in the colour display tube. A known device, described in U.S. Pat. No. 3,725,831, consists of at least four permanent magnetic rings arranged in pairs which generate a magnetic field that can be adjusted as regards position and intensity. The adjustability is obtained by turning the two rings of a pair in the same direction with respect to the electron beams and by turning the one ring in the opposite direction with respct to the other ring. The adjustability necessitates that the rings be arranged on a support which is arranged about the neck of the colour display tube and which should include facilities such that the adjustability of each pair of rings, independent of the position of the other rings, is ensured. The invention has for its object to provide a method whereby a device for converging electron beams can be manufactured which need not be mechanically adjustable, so that it can have a very simple construction, and to provide a colour display tube including such a device.

To this end, the method according to the invention is characterized in that the colour display tube is activated, after which data concerning the extent and the direction of the convergence error of each electron beam are determined, on the basis of which is determined the polarity and intensity of magnetic poles of a structure for generating a permanent, multi-pole, static magnetic field for the correction of the convergence errors occurring in the colour display tube, about the neck of the colour display tube there being provided an auxiliary device for generating variable magnetic fields in the neck of the colour display tube, the auxiliary device being subsequently adjusted such that a magnetic field with converges the electron beams is produced, data being derived from the adjustment of the auxiliary device thus obtained, the said data being a measure for the convergence errors and being used for determining the structure generating the permanent static magnetic field.

Using the described method, a device can be manufactured which generates a magnetic field adapted to the colour display tube and which thus constitutes one unit as if it were with the colour display tube. If desired colour purity errors as well as convergence errors can be eliminated by this method. The convergence errors visible on the screen can be measured and expressed in milimeters of horizontal and vertical errors. The errors thus classified represent data whereby, using magnetic poles of an intensity to be derived from the errors, there can be determined a structure of a magnetic multi-pole which generates a permanent magnetic field adapted to the determined convergence errors.

As a result of the generation of a desired magnetic field by means of an auxiliary device and the derivation of data therefrom, it is possible to determine a device adapted to the relevant colour display tube. Simultaneously, it is ensured that the convergence of the electron beams can be effected.

A preferred version of the method according to the invention is characterized in that for the auxiliary device is used an electromagnetic convergence unit which comprises a number of coils wherethrough electrical currents are conducted in order to generate a magnetic field required for the convergence of the electron beams, the values of the electrical currents producing the data for determining an annular permanent magnetic structure. Because the electrical currents whereby the auxiliary device is actuated are characteristic of the magnetic field generated, the intensity and the position of the poles of the magnetic multi-poles to be used for the colour display tube are determined by the determination of the values of the electrical currents.

The data obtained from the auxiliary device can be used in various manners. The data from the auxiliary device can be stored in a memory, or the data from the auxiliary device can be used immediately for controlling a magnetizing unit which magnetizes an annular magnetizable structure. Alternatively it is possible to convert the data into a code; on the basis thereof an annular permanent magnetic structure having a desired magnetic field strength can be taken or composed from a set of already magnetized structural parts. Obviously, the latter two possibilities can be performed after the data have been stored in a memory.

A simplification of the method is achieved when the device is formed from a magnetizable mass which is provided in the form of a ring on at least one wall of the neck of the colour display tube. The device to be magnetized is thus arranged around the electron beams to be generated. Subsequently, a construction which comprises the auxiliary device and the magnetizing unit is arranged around the neck of the colour display tube. The auxiliary device is then adjusted, after which the construction can possibly be displaced, so that the magnetizing unit encloses the device. The magnetizing unit is actuated on the basis of the data received from the auxiliary device, and magnetizes the device.

In order to make the construction of a magnetizing unit as simple and as light as possible, it is advantageous to polarize material of the structure to be magnetized one area after the other by means of the magnetizing unit. A suitable alternative of the method for which use can be made of the described construction of the magnetizing unit is characterized in that the device consists of a non-magnetizable support and a number of permanent magnetic bipoles. It was found that any feasible magnetic field required for the static convergence of electron beams in a neck of a colour display tube can be comparatively simply generated using at least one eight-pole electromagnetic convergence unit. Similarly, any desired magnetic field can be generated using a twelve-pole electromagnetic convergence unit. It is to be noted that electromagnetic convergence units have already been proposed in U.S. Pat. No. 4,027,219.

The invention will be described in detail hereinafter with reference to a drawing.

FIG. 1 is a diagrammatic representation of a first version of the method according to the invention.

FIG. 2 is a diagrammatic representation of a second version of the method according to the invention.

FIG. 3 shows a preferred embodiment of an auxiliary device.

FIG. 4 is a side elevation of a first embodiment of a device manufactured using the method according to the invention.

FIG. 5 is a cross-sectional view of the embodiment shown in FIG. 4.

FIG. 6 is a side elevation of a further embodiment of a device manufactured using the method according to the invention.

FIG. 7 is a cross-sectional view of the device shown in FIG. 6.

FIG. 8 is a diagrammatic perspective view of a magnetizing device and a convergence unit arranged therein.

FIG. 9a is a cross-sectional view of a convergence unit manufactured using a method according to the invention.

FIG. 9b is a partial side elevation of part of a support of the convergence unit shown in FIG. 9a.

FIG. 9c shows a permanent magnetic structural part of the device shown in FIG. 9a.

The method according to the invention will be described with reference of FIG. 1. An electromagnetic auxiliary device 5 is arranged around the neck 3 of the colour display tube 1. The auxiliary device 5 will be described in detail with reference to FIG. 3. Electrical currents which generate a magnetic field are applied to the auxiliary device 5. When the electrical currents are adjusted to the correct value, a magnetic field adapted to the colour display tube 1 as regards position and intensity is generated. The electrical currents are measured by means of the measuring unit 9. The electrical currents represent data which completely describe the magnetic field generated by the auxiliary device 5. The data are stored in a memory 19 (for example, a ring core memory) in an adapted form (digitally). The data can be extracted from the memory 19 again for feeding a control unit 11. The control unit 11 actuates a magnetizing unit 13. A magnetic field is impressed on the device 15 arranged inside the magnetizing unit 13 (shown to be arranged outside this unit in FIG. 1), the said magnetic field equalling the magnetic field generated by the auxiliary device 5 at the area of the electron beams. The auxiliary device 5 is then removed from the neck 3 and replaced by the device 15.

The method is suitable for the application of an automatic process controller 17. The storage of the data in the memory 19, the retrieval thereof, the determination and the feeding of the data to the control unit 11 are operations which are very well suitable for execution by an automatic controller. Similarly, the process controller 17 can dispatch commands at the correct instants to mechanisms which inter alia arrange the auxiliary device 5 on the display tube 1, arrange the device 15 to be magnetized in the magnetizing unit 13, remove the auxiliary device 5 from the display tube 1, and arrange the device 15 on the neck 3 of the display tube 1. Besides these controlling functions, checking functions can also be performed by the process controller, such as the checking of:

the position of the display tube 1 with respect to the auxiliary device 5.

the determination of the number of data by the measuring unit 9.

the actuation of the magnetizing unit 13.

the position of the device 15 with respect to the display tube 1.

The method shown in FIG. 2 is an alternative to the method described with reference to FIG. 1. The auxiliary device 5 and the magnetizing unit 13 are accommodated together in one construction 6. Before the auxiliary device 5 and the magnetizing unit 13 are arranged around the neck 3 of the colour display tube 1, the as yet unmagnetized device 15 is arranged in a desired position. The auxiliary device 5 is activated and adjuste so that a magnetic field converging the electron beams is produced. Subsequently, the measuring unit 9 determines the necessary data whereby the control unit 11 is adjusted. The auxiliary device 5 may be shifted so that the magnetizing unit 13 encloses the device 15. After the current to the auxiliary device 5 has been interrupted, the magnetizng unit 13 is activated by the control unit 11. After magnetization of the device 15, the auxiliary device 5 and the magnetizing unit 13 are removed. A convergence unit which has been exactly adjusted as regards position and strength has then been arranged on the neck 3 of the tube 1.

FIG. 3 more or less diagrammatically shows an embodiment of an auxiliary device 5. The auxiliary device 5 comprises an annular ferromagnetic core 21 having formed thereon eight pole shoes a, b, c, d, e, f, g, and h which are situated in one plane and radially orientated. Each pole shoe has provided thereabout a winding wherethrough a direct current I to be adjusted is to be conducted.

In the space enclosed by the core 21 an eight-pole static magnetic field is generated whose polarity and intensity can be controlled. The value and the direction of the direct currents Ia, Ib, Ic, Id, Ie, If, Ig and Ih can be adjusted on the basis of the value and the direction of the deviations of the electron beams to be converged. The corrections required for achieving colour purity and convergence can be derived from the value and the direction of the direct currents Ia and Ih which form the data from which the necessary corrections are determined.

A similar embodiment can be used for the magnetizing unit, but because the electrical currents required for converging electron beams are smaller than the currents required for magnetizing the device, the conductors of the coils of the magnetizing unit must be constructed in a different manner which takes account the higher current intensities. If a similar embodiment of the auxiliary device has been made suitable for higher current intensities, it can also operate at lower current intensities. It follows that it is possible also to use the magnetizing unit as the auxiliary device, which is in one case connected to the measuring unit and in the other case to the control unit.

FIG. 4 shows a partly cut-away neck 3 having an envelope 31 of a colour display tube, the flared portion and the adjoining display screen not being shown. At the end of the neck 3 there are provided contact pins 33 to which cathodes and electrodes of the system of electron guns 35 are connected. The device 15 for the static convergence of the electron beams generated by the system of guns 35 consists of a support 15A of synthetic material and a ferrite ring 15B. On the jacket surface of the support 15A is provided a ridge 15c which extends in the longitudinal direction; the ferrite ring 15B is provided with a slot which co-operates therewith and which opens into the edge of the ring on only one side, so that the ring 15B can be secured to the carrier 15A in only one way. FIG. 5 is a cross-sectional view which clearly shows the ridge 15C and the slot of the device 15. The references used in FIG. 5 correspond to those used in FIG. 4.

FIG. 6 shows the same portions of the neck 3 of a colour display tube as FIG. 4. Instead of a support on which a ferrite ring is secured, the device consists only of a layer of ferrite 15 which is secured directly to the inner wall 37 of the neck 3 by means of a binding agent. This offers the advantage that a support which requires space and material can be dispensed with. FIG. 7 is a cross-sectional view and illustrates the simplicity of the device 15. The references used correspond to the references of FIG. 6. The device 15 can also be mounted (not shown in the Figure) on the rear of a deflection unit of the colour display tube. It is alternatively possible to arrange the device on grids or on the cathodes in the neck of the colour display tube.

FIG. 8 diagrammatically shows a magnetizing unit 13 whereby the device 15 arranged thereon is magnetically polarized one location after the other. The extent of the polarization is dependent of the value and direction of the used direct current Im and of the number of ampere-turns of the coil 41 arranged about the core of the magnetizing unit 13. The core consists of two portions 43 and 45 which form a substantially closed magnetic circuit. Between a concave pole shoe 47 and a convex pole shoe 49 of the core portions 43 and 45, respectively, there is a space wherein a portion of the device 15 to be magnetized is arranged. The concave and convex pole shoes 47 and 49 preferably are shaped to follow the curved faces 51 and 53 of the device substantially completely. In order to enable easy arrangement and displacement of the device between the pole shoes 47 and 49, the core portions 43 and 45 are provided with ground contact faces 55 and 57 which are perpendicular to each other. The pole shoes 47 and 49 can be moved away from and towards each other, the core portions 43 and 45 always returning to the same position relative to each other due to the faces 55 and 57 perpendicularly extending to each other. At the same time, the magnetic contact resistance at the faces 55 snd 57 is low and constant, so that the necessary unambiguous relationship between the current Im and the magnetic field generated in the core is ensured.

FIGS. 9a, b and c show a preferred embodiment and details of a static convergence device 15. The device 15 consists of a support 61 of synthetic material, for example, polycarbonate, wherein eight ferromagnetic discs (or "inserts") 63 are equidistantly arranged along the circumference. It will be obvious that this embodiment is particularly suitable for being actuated in a magnetizing unit as shown in FIG. 8. The holes 65 provided in the support 61 are slightly elliptical so as to lock the capsules 63 firmly in the holes 65. To this end, the width b is chosen to be slightly smaller than the height h which equals the diameter d of the round discs (or "inserts") 63. The narrow portions 67 of the support 61 with clamp the disc 63 in the hole 65 due to their elastic action. It is, of course, possible to magnetize the disc 63 before they are arranged in the support 61; the sequence in which the disc 63 are arranged in the support 61 should then be carefully checked.

If a method is used where the most suitable structure is selected from a series of permanent magnetic structures on the basis of the adjusting data, it is advantageous to compose this structure from a number of permanent rings. This will be illustrated on the basis of an example involving superimposition of a four-pole field and a six-pole field. Assume that the magnetic fields can each have M different intensities, and that the on field can occupy N different positions with respect to the other field. If the magnetic structure consists of one permanent magnetic ring, the series from which selection can be made consists of M×M×N rings. If the structure consists of two rings, the series comprises M+M rings, but it should then be possible for the one ring to be arranged in N different positions with respect to the other ring. If the static convergence device is composed as shown in FIG. 9a, b and c or similar, only M kinds of structural parts (discs) having a different magnetical intensity are required for achieving any desired structure.

Color television display tube with coma correction ELECTRON GUN STRUCTURE PHILIPS CRT TUBE 45AX



A color television display tube including an electron gun system (5) in an evacuated envelope for generating three electron beams whose axes are co-planar. The beams converge on a display screen (10) provided on a wall of the envelope and are deflected in the operative display tube across the display screen into two orthogonal directions. The electron gun system (5) has correction elements for causing the rasters scanned on the display screen by the electron beams to coincide as much as possible. The correction elements include annular elements (34) of a material having a high magnetic permeability which are positioned around the two outer beams. In
addition a further correction element (38, 38", 38"') of a material having a high magnetic permeability is provided around the central beam in a position located further from the screen in order to correct field coma errors at the ends of the vertical axis and in the corners to an equal extent. The further element is preferably positioned in, or on the screen side of, the area of the focusing gap of the electron gun.



1. A color display tube comprising an envelope containing a display screen, and an electron gun system for producing a central electron beam and first and second outer electron beams having respective axes which lie in a single plane and converge toward a point on the screen, the electron gun system including an end from which the electron beams exit into a deflection field region of the envelope where a field deflection field effects deflection of the beams in a direction perpendicular to said plane and a line deflection field effects deflection of the beams in a direction parallel to said plane, said line deflection field producing a positive lens action;

characterized in that the electron gun system includes field coma-correcting means comprising:

(a) first and second deflection field shaping means of magnetically-permeable material arranged adjacent the respective outer electron beams, at the end of the electron gun system, for cooperating with the positive lens action of the line deflection field to anisotropically overcorrect the field coma error of said outer electron beams relative to that of the central electron beam; and

(b) a third deflection field shaping means of magnetically-permeable material arranged adjacent the central electron beam, at a position in the electron gun system further from the screen than the first and second field shaping means, for cooperating with the positive lens action of the line deflection field to reverse-anisotropically correct the field coma error of the central electron beam by an amount sufficient to compensate for the overcorrection by the first and second field shaping means, thereby effecting production of a central-electron-beam- produced raster which is substantially identical to the outer-electron-beam-produced rasters.

2. A color display tube comprising an envelope containing a display screen, and an electron gun system for producing a central electron beam and first and second outer electron beams having respective axes which lie in a single plane and converge toward a point on the screen, the electron gun system including at an end thereof a first plate-shaped part including a central and first and second outer apertures from which the respective electron beams exit into a deflection field region of the envelope where a field deflection field effects deflection of the beams in a direction perpendicular to said plane and a line deflection field effects deflection of the beams in a direction parallel to said plane, said line deflection field producing a positive lens action;

characterized in that the electron gun system includes field coma-correcting means comprising:

(a) first and second deflection field shaping means of magnetically-permeable material arranged adjacent the respective outer apertures in the first plate-shaped part for cooperating with the positive lens action of the line deflection field to anisotropically overcorrect the field coma error of said outer electron beams relative to that of the central electron beam; and

(b) a third deflection field shaping means of magnetically-permeable material arranged adjacent a central aperture in a second plate-shaped part of the electron gun for passing the central electron beam, at a position in the electron gun system further from the screen than the first plate-shaped part, for cooperating with the positive lens action of the line deflection field to reverse-anisotropically correct the field coma of the central electron beam by an amount sufficient to compensate for the overcorrection by the first and second field shaping means, thereby effecting production of a central-electron-beam-produced raster which is substantially identical to the outer-electron-beam-produced rasters.

3. A color display tube as in claim 1 or 2 where the third deflection field shaping means comprises first and second strips of magnetically permeable material extending parallel to and symmetrically disposed on opposite sides of said plane. 4. A color display tube as in claim 3 where each of said first and second strips of magnetically permeable material include at opposite ends thereof projecting lugs which extend away from said plane. 5. A color display tube as in claim 3 where the first and second strips of magnetically permeable material comprise integrally formed portions of a cup-shaped portion of the electron gun system, which itself consists essentially of magnetically permeable material. 6. A color display tube as in claim 1 or 2 where the third deflection field shaping means is disposed adjacent an electron-beam-focusing electrode of the electron gun system. 7. A color display tube as in claim 1 or 2 where the first and second deflection field shaping means are disposed on an apertured plate-shaped member closing an end of a centering bush for centering the electron gun system in a neck of the envelope. 8. A color display tube as in claim 7 where the first and second deflection field shaping means comprise ring-shaped elements disposed around respective first and second apertures of said plate-shaped member on a side thereof closer to the screen, and where the third deflection field shaping means comprises a ring-shaped element disposed around a central aperture of said plate-shaped member on a side thereof which is further from said screen. 9. A color display tube as in claim 6 where the third deflection field shaping means comprises a ring-shaped member surrounding a central aperture in the electron-beam-focusing electrode.

Description:

BACKGROUND OF THE INVENTION

The invention relates to a colour television display tube comprising an electron gun system of the "in-line" type in an evacuated envelope for generating three electron beams. The beam axes are co-planar and converge on a display screen provided on a wall of the envelope while the beams are deflected across the display screen into two orthogonal directions by means of a first and a second deflection field. The electron gun system is provided with field shapers for causing the rasters scanned on the display screen by the electron beams to coincide as much as possible. The field shapers comprise elements of a magnetically permeable material positioned around the two outer beams and placed adjacent the end of the electron gun system closest to the screen.

A colour television display tube of this type is known from U.S. Pat. No. 4,196,370. A frequent problem in colour television display tubes incorporating an electron gun system of the "in-line" type is what is commonly referred to as the line and field coma error. This error becomes manifest in that the rasters scanned by the three electron beams on the display screen are spatially different. This is due to the eccentric location of the outer electron beams relative to the fields for horizontal and vertical deflection, respectively. The Patent cited above sums up a large number of patents giving partial solutions. These solutions consist of the use of field shapers. These are magnetic field conducting and/or protective rings and plates mounted on the extremity of the gun system which locally strengthen or weaken the deflection field or the deflection fields along part of the electron beam paths.

In colour television display tubes various types of deflection units may be used for the deflection of the electron beams. These deflection units may form self-convergent combinations with tubes having an "in-line" electron gun system. One of the frequently used deflection unit types is what is commonly referred to as the hybrid deflection unit. It comprises a saddle line deflection coil and a toroidal field deflection coil. Due to the winding technique used for manufacturing the field deflection coil it is not possible to make the coil completely self-convergent. Usually such a winding distribution is chosen that a certain convergence error remains, which is referr

ed to as field coma. This coma error becomes clearly noticeable in a larger raster (vertical) for the outer beams relative to the central beam. The vertical deflection of the central beam is smaller than that of the outer beams. As has been described, inter alia, in the U.S. Pat. No. 4,196,370 cited above, this may be corrected by providing elements of a material having a high magnetic permeability (for example, mu-metal) around the outer beams. The peripheral field is slightly shielded by these elements at the area of the outer electron beams so that these beams are slightly less deflected and the field coma error is reduced.

A problem which presents itself is that the correction of the field coma (Y-coma) is anisotropic. In other words, the correction in the corners is less than the correction at the end of the vertical axis. This is caused by the positive "lens" action of the line deflection coil (approximately, quadratic with the line deflection) for vertical beam displacements. (The field deflection coil has a corresponding lens action, but it does not contribute to the relevant anisotropic effect). The elimination of such an anisotropic Y-coma error by adapting the winding distribution of the coils is a cumbersome matter and often introduces an anisotropic X-coma.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a display tube in which it is possible to correct field coma errors on the vertical axis and in the corners to an equal extent without requiring notable adaptation of the winding distribution of the coils.

To this end a display tube of the type described in the opening paragraph is characterized in that the elements placed at the display screen end of the electron gun system are constructed to overcorrect field coma errors and that the field shapers comprise a further element positioned around the central electron beam at an area of the electron gun system further away from the display screen which operates oppositely to the elements at the end.

The invention is based on the recognition of the fact that the problem of the anisotropic Y-coma can be solved by suitably utilizing the Z-dependence of the anisotropic Y-coma.

This dependence implies that as the coma correction is effected at a larger distance (in the Z-direction) from the "lens" constituted by the line deflection coil the operation of said "lens" becomes more effective, so that the coma correction acquires a stronger anisotropic character. With the coma correction means placed around the outer beams at the gun extremity closest to the screen, the coma is the overcompensated to such a large extent that it is overcorrected even in the corners. The coma is then heavily overcorrected on the vertical axis. The correction is anisotropic. A stronger anisotropic anti-correction is brought about by performing an anti-coma correction at a still greater distance from the lens. By adding this stronger anisotropic anti-correction the coma on the vertical axis can be reduced to zero without the coma in the corners becoming anisotropic. The coma on the vertical axis and the corners is then corrected to an equal extent.

The further element may have the basic shape of a ring and may be mounted around the central aperture of an apertured electrode partition. However, restrictions then are imposed on the positioning of the further element. As will be further described hereinafter, there will be more freedom in the positioning of the further element when in accordance with a preferred embodiment of the invention the further element comprises two strips of a magnetically permeable material which extend parallel to and symmetrically relative to the plane through the electron beam axis around the axis of the central beam.

The effectiveness of these strips may be improved under circumstances when according to a further embodiment of the invention their extremities are provided with outwardly projecting lugs.

The strips may further be separate components or form one assembly with a magnetic material cup-shaped part of the electron gun system, which facilitates mounting.

An effective embodiment of the invention is characterized in that the further element is positioned in, or in front of, the area of the focusing gap of the electron gun. This may be realized in that the further element consists of a ring of magnetically permeable material which is mounted around the central aperture of an apertured partition in the focussing electrode.

The principle of the invention is realised in a given case in that the field shapers adjacent the display screen facing end of the electron gun system consist of two rings mounted on the apertured lid of a box-shaped centering bush, while the further element in that case may advantageously consist of a ring of magnetically permeable material which is mounted around the central aperture in the bottom of the centering bush.

The display tube according to the invention is very suitable for use in a combination with a deflection unit of the hybrid type, particularly when a combination is concerned which should be free from raster correction.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be further described by way of example, with reference to the accompanying drawing figures in which

FIG. 1 is a perspective broken-up elevational view of a display tube according to the invention;

FIG. 2 is a perspective elevational view of an electron gun system for a tube as shown in FIG. 1;

FIG. 3a is an elevational view of a vertical cross-section through part of FIG. 2 ; and

FIG. 3b is a cross-section analogous to FIG. 3a of a further embodiment according to the invention; and

FIG. 3c is a cross-section analogous to FIG. 3a of a further embodiment according to the invention;

FIGS. 4a, b, c and d show the field coma occurring in the different deflection units;

FIG. 4e illustrates the compensation of the field coma according to the invention;

FIG. 5a schematically shows the beam path on deflection in a conventional dislay tube, and

FIG. 5b schematically shows the beam path on deflection in a display tube according to the invention; and

FIGS. 6a, b, c and d are longitudinal sections of different embodiments of an electron gun system for a display tube according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a perspective elevational view of a display tube according to the invention. It is a colour television display tube of the "in-line" type. In a glass envelope 1, which is composed of a display window 2, a cone 3 and a neck 4, this neck accommodates an integrated electron gun system 5 generating three electron beams 6, 7 and 8 whose axes are co-planar prior to deflection. The axis of the central electron beam 7 coincides with the tube axis 9. The inside of the display window 2 is provided with a large number of triplets of phosphor elements. These elements may be dot shaped or line shaped. Each triplet comprises an element consisting of a blue-luminescing phosphor, an element consisting of a green-luminescing phosphor and an element consisting of a red-luminescing phosphor. All triplets combined constitute the display screen 10. Positioned in front of the display screen is a shadow mask 11 having a very large number of (elongated) apertures 12 which allow the electron beams 6, 7 and 8 to pass, each beam impinging only on respective phosphor elements of one colour. The three co-planar electron beams are deflected by a system of deflection coils not shown. The tube has a base 13 with connection pins 14.

FIG. 2 is a perspective elevational view of an embodiment of an electron gun system as used in the colour television display tube of FIG. 1. The electron gun system has a common cup-shaped electrode 20, in which three cathodes (not visible in the Figure) are secured, and a common plate-shaped apertured grid 21. The three electron beams whose axes are co-planar are focused with the aid of a focussing electrode 22 and an anode 23 which are common for the three electron beams. Focussing electrode 22

consists of three cup-shaped parts 24, 25 and 26. The open ends of parts 25 and 26 are connected together. Part 25 is coaxially positioned relative to part 24. Anode 24 has one cup-shaped part 27 whose bottom, likewise as the bottoms of the other cup-shaped parts, is apertured. Anode 23 also includes a centering bush 28 used for centering the electron gun system in the neck of the tube. This centering bush is provided for that purpose with centering springs not shown. The electrodes of the electron gun system are connected together in a conventional manner with the aid of brackets 29 and glass rods 30.

The bottom of the centeri

ng bush 28 has three apertures 31, 32 and 33. Substantially annular field shapers 34 are provided around the apertures 31 and 33 for the outer electron beams. The centering bush is for example 6.5 mm deep and has an external diameter of 22.1 mm and an internal diameter of 21.6 mm in a tube having a neck diameter of 29.1 mm. The distance between the centers of two adjacent apertures in the bottom is 6.5 mm. The annular elements 34 are punched from 0.40 mm thick mu-metal sheet material. (Conventional elements generally have a thickness of 0.25 mm).

FIG. 3a is an elevational view of a vertical cross-section through the cup-shaped part 25 of the electron gun system of FIG. 2 in which the plane through the beam axes is perpendicular to the plane of the drawing. Two (elongated) strips 35 of a magnetically permeable material such as mu-metal are provided symmetrically relative to the aperture 37 for the central electron beam.

FIG. 3b shows a cross-section analogous to the cross-section of FIG. 3a of a further embodiment of the strips 35. In this case each strip has projecting lugs 36.

The strips 35 which produce a coma correction in a direction opposite to the direction of the coma correction produced by the elements 34 are shown as separate components secured to the focussing electrode 22 (for example, by means of spotwelding). If the cup-shaped part 24 has a magnetic shielding function and is therefore manufactured of a magnetically permeable material, the strips 35 may be formed in an alternative manner as projections on the cup-shaped part 24.

FIG. 3c is an elevational view of a cross-section at a different area through the anode 22 in an alternative embodiment of the electron gun system of FIG. 2. In this alternative embodiment the strips 35 are absent. They have been replaced by an annular element 38 of a magnetically permeable material positioned around the center beam. The annular element 38 is provided on an additional apertured partition 39 accommodated between the cup-shaped parts 25 and 26.

In this embodiment there is a restriction that such an additional partition cannot be accommodated in any arbitrary position. The embodiments shown in FIGS. 3a and 3b do not have such a restriction. The strips 35 may be provided in any axial position of the component 22 dependent on the effect to be attained. A plurality of variants based on the embodiment shown in FIG. 3c is, however, possible. For this purpose reference is made to FIG. 6.

The effect of the invention is demonstrated with reference to FIG. 4. In FIG. 4a the rasters of the outer electron beams (red and blue) and the central beam (green) are shown by means of a solid and a broken line, respectively, in a display tube without field shapers and provided with a self-convergent deflection coil. The reference bc indicates the field coma.

Correction of the coma with the means hitherto known results in the situation shown in FIG. 4b. The field coma is zero at the ends of the Y-axis (the vertical axis or picture axis), but in the corners the field coma is still not zero.

Overcompensation of the field coma causes the situation shown in FIG. 4c. Overcompensation is realised, for example, by adapting the external diameter of the annular elements 34 shown in FIG. 2, or by placing them further to the front.

A coma correction in the opposite direction is realised with the aid of the elements 35 or the element 38 in a position located further to the rear in the electron gun system. The effect of this "anti"-coma correction by itself is shown in FIG. 4d.

The combined effect of the corrections as shown in FIGS. 4c and 4d is shown in FIG. 4e. The effect of the invention can clearly be seen; the field coma is corrected to an equal extent on the vertical axis and in the corners.

Elaboration of the step according to the invention on the beam path of the electron beams in a display tube is illustrated with reference to FIGS. 5a and b. FIG. 5a is a longitudinal section through a display tube 40 in which the outer electron beams R, B and the central electron beam G are deflected in a conventional manner. The reference L indicates the position where the "lensing action" of the deflection coils is thought to be concentrated. Upon generating a change in direction, a displacement (ΔY) of the outer beams relative to the central beam occurs in the "lens".

The step according to the invention ensures that there is no displacement in the lens of the outer beams relative to the central beam when generating a change in direction (FIG. 5b).

When using an annular element provided around the central aperture in an apertured partition, such as the element 38, for ensuring an anti-coma correction, there are different manners of positioning the element in a suitable place in addition to the manner of positioning previously described with reference to FIG. 3c. Some of these manners are shown with reference to FIGS. 6a, b, c and d showing longitudinal sections through different electron gun systems suitable for use in a display tube according to the invention. The plane through the axes of the electron beams is in the plane of the drawing.

FIG. 6a shows the same situation as FIG. 3c. An additional apertured partition 39 on which a ring 38 of a magnetically permeable material is mounted around the central aperture is provided between the parts 25 and 26 of the focussing electrode 22 (G3). If no additional partition 39 is to be accommodated, it is possible to provide an anti-coma correction ring 38' around the central aperture on the bottom 41 of the cup-shaped part 24. However, one should then content oneself with the effect that is produced by the ring positioned in this particular place.

As FIG. 6b shows, an alternative manner is to provide an additional partition 42 between the electrode parts 24 and 25 and mount a ring 38' of a magnetically permeable material on it. This is, however, only possible when the cup-shaped part 24 does not have a shielding function.

There is a greater variation in the positioning possibilities of the anti-coma correction element when the electron gun system is of the multistage type, as is shown in FIG. 6c. Broken lines show that one or more rings of a megnetically permeable material may be provided in different positions around the axis of the central beam.

The closer the correction elements 34 around the outer beams are placed towards the display screen, the better it is in most cases. To meet this purpose, an electron gun system having a special type of centering bush as shown in the electron gun system of FIG. 6d can be used. In that case the centering bush 28 is box-shaped and provided with an apertured end 46 on the side facing the display screen.

The apertured end 46 has three apertures 43, 44 and 45. Rings 34 of a magnetically permeable material are mounted on the outside of the end 46 at the aperture 43 and 45 for the outer beams. An optimum position, viewed in the longitudinal direction of the electron gun system, can then always be found for the ring 38 of a magnetically permeable material which is to be positioned around the central beam. This may be the position of ring 38 in FIG. 6d, but also a more advanced position indicated by the ring 38". Even a still more advanced position indicated by ring 38"' is possible. Generally, a position of the ring around the central beam in, or in front of the area of the focusing gap 47 of the electron gun, that is to say, in or in front of the area of the transition from part 26 to part 27 is very suitable. The rings around the outer beams should then be located further to the front, into the direction of the display screen.