A steel structure is supporting the chassis parts and the cabinet robustness.
On the left side is located the line + EHT section, all signal parts are located on the main chassis.
Power supply is on top side with mains trasformer.
The tuning circuits has a large knob potentiometers tuning system which use voltage controlled capacitances such as varactor diodes as the frequency determining elements.
How AFC Circuit Works in B/W Analog Television Receiver:
Push-Button
tuning on u.h.f. while being very convenient often leaves a margin of
mistuning, especially after some wear and tear has occurred on the
mechanism. Even dial tuning can lead to errors due to the difficulty
many people experience in judging the correct point. Oscillator drift
due to temperature changes can also cause mistuning. Automatic frequency
control (a.f.c.) will correct all these faults. The vision carrier when
the set is correctly tuned on u.h.f. is at 39.5MHz as it passes down
the i.f. strip. Thus if at the end of the i.f. strip a discriminator
tuned circuit is incorporated centred on 39.5MHz the discriminator
output will be zero at 39.5MHz and will move positively' one side of
39.5MHz and negatively the other as the tuning drifts. This response is
shown in Fig. 1.If the tuning is not correct then the discriminator output is not zero and if this output is applied to change the reverse bias on a tuning diode mounted in the oscillator section of the u.h.f. tuner it will correct most of the error. Tuning, varicap or varactor diodes-to give them a few of their names-are junction diodes normally operated with reverse bias but not sufficient to bias them into the breakdown region in which zener diodes operate. The greater the reverse bias the lower their capacitance: a typical curve, for the PHILIPS BB105 or STC BA141 tuning diode, is shown in Fig. 2. All diodes e
xhibit
this basic type of characteristic but special diodes have to be used
for u.h.f. because they must not introduce any excessive loss into the
tuned circuits they control. In other words, just as a coil has to have a
good Q so does a varicap diode. Normally, we don't worry about the Q of
a capacitor as it is usually very good. However, a tuning diode is not a
true capacitor. It has, for example, leakage current so the Q of the
diode is a factor which has to be considered. The diode manufacturer
however will have considered these points and if you buy a diode
specified for u.h.f. use you will have no trouble. These points have
been mentioned to clear up any misunderstandings and to show why any old
diode won't do.Basic AFC System
To return to our TV set, if the oscillator frequency is too high then the vision carrier frequency will also be too high and in the simple arrangement shown in Fig. 3 the discriminator will give a negative signal to decrease the bias on the tuning diode thus increasing its
capacitance
and in turn reducing the oscillator frequency and correcting the error.
Note that in this diagram the reverse bias on the diode is applied to
its cathode. It is therefore positive with respect to ground so that a
negative signal from the discriminator will reduce the positive voltage
on the diode thus reducing its bias and increasing its capacitance. In
this arrangement the diode is biased somewhere near the mid point of its
characteristic by the positive d.c. bias fed into one side of the
discriminator. The discriminator thus adds to or subtracts from this
d.c. bias.AFC Loop Gain:
The amount by which the error is reduced depends on the gain of the circuit. An estimate of the gain required must first be made by guessing how much error is likely to be given by your push -buttons or hand tuning: 1MHz would be an outside figure as a tuning error of that magnitude would produce a very bad picture of low definition in one direction and badly broken up in the other. This error should be reduced to
about
100kHz to be really unnoticeable, indicating a required gain of ten. In
fitting a.f.c. to an existing set some measure- ments should be done as
an experiment before finally deciding on the circuit gain. The first
thing to do is to add the suggested discriminator to the i.f. strip. As
the circuit (Fig. 4) shows a Foster -Seeley type discriminator is used
and with the coils specified and the driver circuit shown it should give
±4V for 0.5MHz input variation.EXAMPLE of Circuit Description:
The driver stage Tr1 takes a small sample signal from the i.f. strip but this should be large enough to drive Tr1 into saturation. That is to say Tr1 is a limiter stage so that the signal amplitude applied to the discriminator coil L2 stays constant over the normal range of signal levels. Trl is biased at approximately 7mA which, according to the original report ("Simple a.f.c. system for 625 -line TV receivers" by P. Bissmire, PHILIPS Technical Communications, March, 1970), gives the best limiting performance. C1, R
14
and R3 damp the stage to prevent oscillation. C2 decouples the power
feed and should be close to the circuit. The coil former and can are the
normal ones used for TV sets and so should be easily obtainable: the
former diameter is 5mm. and length 40mm. and winding details are given
in Fig. 5.The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the developed apparates both tubes or transistors.
Therefore a stable AFC circuit is developed:
A superheterodyne receiver having an automatic intermediate frequency control circuit with means to prevent the faulty regulation thereof. The receiver has means for receiving a radio frequency signal and mixing the same with the output of a superheterodyne oscillator. This produces an intermediate frequency signal which is coupled to a frequency or phase discriminator to produce an error signal for controlling the frequency of the superheterodyne oscillator. A regulation circuit is provided having an electronic switch to interrupt the feedback circuit when only unwanted frequencies tend to produce faulty regulation of the superheterodyne oscillator.
Power supply is realized with mains transformer and Linear transistorized power supply stabilizer, A DC power supply apparatus includes a rectifier circuit which rectifies an input commercial AC voltage. The rectifier output voltage is smoothed in a smoothing capacitor. Voltage stabilization is provided in the stabilizing circuits by the use of Zener diode circuits to provide biasing to control the collector-emitter paths of respective transistors.A linear regulator circuit according to an embodiment of the present invention has an input node receiving an unregulated voltage and an output node providing a regulated voltage. The linear regulator circuit includes a voltage regulator, a bias circuit, and a current control device.
The bias circuit may include a bias device and a current source. The bias device has a first terminal coupled to the output terminal of the voltage regulator and a second terminal coupled to the control electrode of the current control device. The current source has an input coupled to the first current electrode of the current control device and an output coupled to the second terminal of the bias device. A capacitor may be coupled between the first and second terminals of the bias device.
In the bias device and current source embodiment, the bias device may be implemented as a Zener diode, one or more diodes coupled in series, at least one light emitting diode, or any other bias device which develops sufficient voltage while receiving current from the current source. The current source may be implemented with a PNP BJT having its collector electrode coupled to the second terminal of the bias device, at least one first resistor having a first end coupled to the emitter electrode of the PNP BJT and a second end, a Zener diode and a second resistor. The Zener diode has an anode coupled to the base electrode of the PNP BJT and a cathode coupled to the second end of the first resistor. The second resistor has a first end coupled to the anode of the Zener diode and a second end coupled to the reference terminal of the voltage regulator. A second Zener diode may be included having an anode coupled to the cathode of the first Zener diode and a cathode coupled to the first current electrode of the current control device.
A circuit is disclosed for improving operation of a linear regulator, having an input terminal, an output terminal, and a reference terminal. The circuit includes an input node, a transistor, a bias circuit, and first and second capacitors. The transistor has a first current electrode coupled to the input node, a second current electrode for coupling to the input terminal of the linear regulator, and a control electrode. The bias circuit has a first terminal for coupling to the output terminal of the linear regulator and a second terminal coupled to the control electrode of the transistor. The first capacitor is for coupling between the input and reference terminals of the linear regulator, and the second capacitor is for coupling between the output and reference terminals of the linear regulator. The bias circuit develops a voltage sufficient to drive the control terminal of the transistor and to operate the linear regulator. The bias circuit may be a battery, a bias device and a current source, a floating power supply, a charge pump, or any combination thereof. The transistor may be implemented as a BJT or FET or any other suitable current controlled device.
Power
Supply: The examples chosen are taken from manufacturers' circuit
diagrams and are usually simplified to emphasise the fundamental nature
of the circuit. For each example the particular transistor properties
that are exploited to achieve the desired performance are made clear. As
a rough and ready classification the circuits are arranged in order of
frequency: this part is devoted to circuits used at zero frequency,
field frequency and audio frequencies. Series Regulator Circuit Portable
television receivers are designed to operate from batteries (usually
12V car batteries) and from the a.c. mains. The receiver usually has an
11V supply line, and circuitry is required to ensure that the supply
line is at this voltage whether the power source is a battery or the
mains. The supply line also needs to have good regulation, i.e. a low
output resistance, to ensure that the voltage remains constant in spite
of variations in the mean current taken by some of the stages in the
receiver. Fig. 1 shows a typical circuit of the power -supply
arrangements. The mains transformer and bridge rectifier are designed to
deliver about 16V. The battery can be assumed to give just over 12V.
Both feed the regulator circuit Trl, Tr2, Tr3, which gives an 11V output
and can be regarded as a three -stage direct -coupled amplifier. The
first stage Tr 1 is required to give an output current proportional to
the difference between two voltages, one being a constant voltage
derived from the voltage reference diode D I (which is biased via R3
from the stabilised supply). The second voltage is obtained from a
preset potential divider connected across the output of the unit, and is
therefore a sample of the output voltage. In effect therefore Tr 1
compares the output voltage of the unit with a fixed voltage and gives
an output current proportional to the difference between them. Clearly a
field-effect transistor could do this, but the low input resistance of a
bipolar transistor is no disadvantage and it can give a current output
many times that of a field-effect transistor and is generally preferred
therefore. The output current of the first stage is amplified by the two
subsequent stages and then becomes the output current of the unit.
Clearly therefore Tr2 and Tr3 should be current amplifiers and they
normally take the form of emitter followers or common emitter stages
(which have the same current gain). By adjusting the preset control we
can alter the fraction of the output voltage' applied to the first stage
and can thus set the output voltage of the unit at any desired value
within a certain range. By making assumptions about the current gain of
the transistors we can calculate the degree of regulation obtainable.
For example, suppose the gain of Tr2 and Tr3 in cascade is 1,000, and
that the current output demanded from the unit changes by 0.1A (for
example due to the disconnection of part of the load). The corresponding
change in Tr l's collector current is 0.1mA and, if the standing
collector current of Tr 1 is 1mA, then its mutual conductance is
approximately 4OmA/V and the base voltage must change by 2.5mV to bring
about the required change in collector current. If the preset potential
divider feeds one half of the output voltage to Tr l's base, then the
change in output voltage must be 5mV. Thus an 0.1A change in output
current brings about only 5mV change in output voltage: this represents
an output resistance of only 0.0552.TAA611-A12 - Dual BTL power audio amplifier
TCA 511 TV HORIZONTAL AND VERTICAL PROCESSOR
The TCA 511 is a silicon monolithic integrated circuit in a 16—lead dual in—line plasticpackage. It incorporates the following functions: high stability horizontal oscillator,
horizontal APC circuit with high noise immunity and large pull—in range, high stability
vertical oscillator and sawtooth generator.
lt is intended for driving TV horizontal and vertical transistorized output stages.
APPLICATION INFORMATION
Power Supply
The circuit can work with stabilized supply voltage having a value from 9 to 15 V.
A dropping resistor and a filter capacitor may be used to obtain the suipply from higher
voltages; however, the voltage on pins 3 and 4 must never exceed the maximum
permitted voltage.
Synchronization
Pins 2 and 6 can be DC driven if the reference level of the synchronization pulses is
less than 1 V. With reference levels greater than this value, a coupling capacitor must
be inserted in series with the input, and pins 2
and 6 must be connected to ground
via a resistor.
Vertical Oscillator
The capacitor connected to pin 1 must be selected with regard to the frequency
tolerance, to the thermal stability and to the capacitor's ageing.
The width of the output pulse, to be chosen according to the needs of the output
stages, is defined by the resistor connected between pin 1 and pin 16.
Vertical Output
The vertical output is taken from pin 14, which is a buffered output of the sawtooth
voltage generated at pin 15.
The output current from pin 14 is defined by an internal resistor in the integrated
circuit. if a greater current is needed, a resistor may be connected between pin 14
and pin 3.
The oscillator output pulse is available at pin 15 if the capacitor C9 is not connected. _
This configuration is used for driving output stages in which the sawtooth is generated
by Miller effect.
Horizontal Oscillator
The capacitor connected between pin 10 and ground must be selected with regard
to the frequency tolerance, 1:0 the thermal stability and to the capacit0r’s ageing.
In multistandard receivers, the oscillation frequency may be changed by switching the
value of the capacitor connected to pin 10.
TBA 311 TV SIGNAL PROCESSING CIRCUIT
The TBA 311 is a monolithic integrated circuit in a 16-lead clual in-line or quad in—Iine
plastic package. It is intended for use as signal processing circuit for black and
white and colour television sets.
The circuit is designed for receivers equipped with tubes or transistors in the deflection
and video output stages, and with PNP or NPN transistors in the tuner and NPN in
the IF amplifier.
Only signals with the negative modulation can be handled by the circuit. The circuit
is protected against short circuit between video output and GND. The TBA 311 includes:
0 VIDEO PREAMPLIFIER with EIMITTER FOLLOWER OUTPUT
0 GATED AGC for VIDEO» IF AMPLIFIER and TUNER
0 NOISE INVERTER CIRCUIT for GATING AGC and SYNC. PULSE SEPARATOR
o HORIZONTAL SYNC. PIULSE SEPARATOR
0 VERTICAL SYNC. PULSE SEPARATOR
0 BLANKING FACILITY for the VIDEO AMPLIFIER.
flyback transformer design code equivalence list:
ORIGINAL AT2042 FOR BRION VEGA REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR BRUNS REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR CENTURY REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR GELOSO REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR GENERAL ELECTRIC REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR KENNEDY REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR KORTING REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR LOEWE / LOEWE-OPTA REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR LUMA ELEKTRONIK REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR LUXOR REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR MAGNADYNE REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR MINERVA REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR MIVAR REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR PHILIPS REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR RECOFIX REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR SALORA REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR SEIMART REPLACEMENT ------------> HR 2268 TRSI
ORIGINAL AT2042 FOR ULTRAVOX REPLACEMENT ------------> HR 2268 TRSI
No comments:
Post a Comment
The most important thing to remember about the Comment Rules is this:
The determination of whether any comment is in compliance is at the sole discretion of this blog’s owner.
Comments on this blog may be blocked or deleted at any time.
Fair people are getting fair reply. Spam and useless crap and filthy comments / scrapers / observations goes all directly to My Private HELL without even appearing in public !!!
The fact that a comment is permitted in no way constitutes an endorsement of any view expressed, fact alleged, or link provided in that comment by the administrator of this site.
This means that there may be a delay between the submission and the eventual appearance of your comment.
Requiring blog comments to obey well-defined rules does not infringe on the free speech of commenters.
Resisting the tide of post-modernity may be difficult, but I will attempt it anyway.
Your choice.........Live or DIE.
That indeed is where your liberty lies.
Note: Only a member of this blog may post a comment.