VOXSON T1741 YEAR 1976.

The VOXSON T1741 is a 17 inches (41cm) b/W portable television with 8 programs keyboard and potentiometers tuning search.

The set is designed by Rodolfo Bonetto for VOXSON.

" Rodolfo Bonetto has drawn many televisions for Voxson at this time, all as well drawn and also different... each others... "


Rodolfo Bonetto

(Milan 1929-1991) designer. Began his activity in 1958 operating in the durable consumer goods sector and industrial goods sector in various fields: from domestic appliances to bathroom fittings, automobiles, musical instruments, radios and airplane instrumentation panels. “A cultured factory worker”, as V. Gregotti described him, he successfully managed to combine a thorough understanding of production technologies and materials with ergonomic considerations and a very ethical attitude to formal research. He taught at the Hochschule für Gestaltung of Ulm (1961-1965), and has been awarded six Compasso d’Oro for objects such as the Sfericlock alarm clock (Veglia Borletti, 1963); the O.C.N. numerical control machine tool (Olivetti, 1967); the automatic microfilm apparatus (BCM, 1970); the interior for the 131 Supermiriafiori (Fiat, 1978). Between 1972 and 1975 with N. Matsunaga, he designed the tooling centre Horizon 2 (Olivetti) up to the Wiz multi-purpose generator. Creator of the Fire engine (1984) for Fiat, the Rotor, public telephone for Sip (1989) and the mechanism for automatic gate opening Cross 6 (Novotecnica), he has been a member of national and international juries and president of Ic sid from 1981 to 1983. Bonetto is the only Italian designer never to have put his name to architectural projects, as he was always solely interested in large-scale production. After his death, he was dedicated the Compasso d’Oro 1991 as a tribute to his overall activity, which now continues with the Bonetto Design Studio, run by his son Marco, who, in 1994, founded the Bonetto Design Centre in Montecarlo dedicated to his father’s memory, a centre for ideas and services for the new areas of design.
[from A. Pansera ( edited by), Italian Design Dictionary, Cantini, Milan 1995, in the updated volume (January 1998, edited by Tiziana Occleppo) from the CD Rom “Navigando nel design” (edited by A . Pansera, art direction Oderso Rubini for Studio Equatore) 1995]

Rodolfo Bonetto had his first meeting with Raimondo Guzzini in 1967, as is shown by an entry in the records in which Bonetto used to carefully note down all his working relationships. He designed for the Fratelli Guzzini until 1971 and up to 1986 for iGuzzini illuminazione.

VOXSON was an Italian manufacturer site in Rome in Italy.

It was founded in 1952 by the engineer Arnaldo Piccinini with the name FARET, which stays for Fabbrica Apparecchi Radio e Televisione S.p.A..

The activity begun with radio and television fabrication factory.

It have had almost an immediate success on the market and at the end of the 1950's it have great penetration in the market with lot of sales even in extra market such as Germany.



With some unclear involvements in the 1980's VOXSON was sinking , and with classics Italian industry destroy style it was treatened like a tennis ball between that and this guy and mate; and all of this degraded rapidly the original identity of this industry.

Today VOXSON is selling LCD crap like many others with parts coming from there and there.

The destiny of such industry seems all around the same.


(To see the Internal Chassis Just click on Older Post Button on bottom page, that's simple !)

Further Notes and readings:

^ Produce autoradio da ventisei anni, in L'Unità, 28 ottobre 1977. ^ G. Dell'Aquila, Alla Voxson non bastano o e sovvenzioni, in L'Unità, 30 agosto 1977. ^ F. Ferrarotti, La città come fenomeno di classe, Editore Franco Angeli, 1975, p. 69 ^ A. Castagnoli, E. Scarpellini, Storia degli imprenditori italiani, Einaudi, 2003, p. 333 ^ (EN) "EMI buys 50 P.C. of Voxson, TV Maker", articolo della rivista Billboard del 24 aprile 1971. ^ "VOXSON / L'EMI VUOLE CEDERE IL POSTO ALLA GEPI", articolo del periodico L'Espresso vol. 21, numero 8 del febbraio 1975. ^ Atti Parlamentari - Camera dei Deputati, SEDUTA DI GIOVEDÌ 29 SETTEMBRE 1977 (PDF), su Legislature.Camera.it, 29 settembre 1977. URL consultato il 22 gennaio 2019.

 ^ Dal sito credfed.it ^ Informazione tratta dal sito europeanmemories.eu ^ "ITT E REL DANNO VITA ALLA VIDITAL ASSORBIRA' 750 LAVORATORI VOXSON", Repubblica, 8 febbraio 1985 ^ "VA A FONDO LA VOXSON COSTRETTA A LICENZIARE", Repubblica, 11 settembre 1987 ^ "QUESTO IL FALLIMENTO REL 377 MILIARDI SPESI NEL NULLA", Repubblica, 2 ottobre 1987 ^ "LA REL ENTRA NELLA VOXSON PER SALVARE 300 OCCUPATI", Repubblica, 9 ottobre 1987 ^ "BATTAGLIA DA' IL VIA AL RIFINANZIAMENTO DELLA VOXSON", Repubblica, 22 ottobre 1987 ^ "SOMMERSI E SALVATI CON I SOLDI REL", Repubblica, 19 ottobre 1990 ^ "REL LIQUIDATA LO STATO 'ESCE' DALL'ELETTRONICA", Repubblica, 21 dicembre 1990 ^ "la Maserati suona l' ultima sirena", Corriere della Sera, 30 marzo 1993 ^ "Aspettando Rete4 Di Stefano fa trading", Corriere della Sera, 25 febbraio 2008

VOXSON T1741 CHASSIS 3.55 INTERNAL VIEW.

The VOXSON T1741 CHASSIS 3.55 is another awesome engineering example.

On a 2 boards development the entire receiver circuitry is featuring all functions.

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.

In one embodiment, the current control device is implemented as an NPN bipolar junction transistor (BJT) having a collector electrode forming the input node of the linear regulator circuit, an emitter electrode coupled to the input of the voltage regulator, and a base electrode coupled to the second terminal of the bias circuit. A first capacitor may be coupled between the input and reference terminals of the voltage regulator and a second capacitor may be coupled between the output and reference terminals of the voltage regulator. The voltage regulator may be implemented as known to those skilled in the art, such as an LDO or non-LDO 3-terminal regulator or the like.
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.

Left sided is realized all signal part and right side all deflections circuits.

- Tba550Q (Plessey)

- TBA550 (PHILIPS)

The TBA550 is a silicon monolithic integrated signal processing circuit for television

receivers. It combines following functions:
- video preamplifier with emitter follower output
- gated a. g. c. detector supplying the a. g. c. voltages for the vision L f. amplifier and
tuner (delayed)
- noise inverter for gating the a. g. c. and sync separator circuits
- sync separator
- automatic horizontal synchronisation
- vertical sync pulse separator
- blanking facility for the video amplifier
The circuit is designed for receivers equipped with tubes or transistors in the deflection and video output stages, and with n-p-n transistors in the tuner and Lf. amplifier.

Only signals with negative modulation can be handled by the circuit.

TAA611-A12 - Dual BTL power audio amplifier

The line deflection is using the

BU109A

A SILICON PNP TRANSISTOR, see below the datasheet:

BU109A

NPN TRANSISTOR, DIFFUSED MESA
TRANSISTOR NPN SILIC/UM, MESA DIFFUSE

The BU 109 is a fast switching high voltage
transistor. It is primarly intended for use in V 330 V
horizontal deflection output stage of black
and white TV receivers fitted with 110° picture tube.

ABSOLUTE RATINGS (LIMITING VALUES) t = 25°C (Unless otherwise stated)

Collector-base voltage VCB 330 V
Collector-emitter voltage 120V

Collector-emitter voltage VBE = -5 V VCEX 330V
Emitter-base volt 10 V
Collector current 10 A
Peak collector current 15A
Base current 3 A
Power dissipation = 25 C 85 W
Storage temperature min. t -65 °C
Temperature de stockage maX +200°c





GENERAL BASIC TRANSISTOR LINE OUTPUT STAGE OPERATION:

The basic essentials of a transistor line output stage are shown in Fig. 1(a). They comprise: a line output transformer which provides the d.c. feed to the line output transistor and serves mainly to generate the high -voltage pulse from which the e.h.t. is derived, and also in practice other supplies for various sections of the receiver; the line output transistor and its parallel efficiency diode which form a bidirectional switch; a tuning capacitor which resonates with the line output transformer primary winding and the scan coils to determine the flyback time; and the scan coils, with a series capacitor which provides a d.c. block and also serves to provide slight integration of the deflection current to compensate for the scan distortion that would otherwise be present due to the use of flat screen, wide deflection angle c.r.t.s. This basic circuit is widely used in small -screen portable receivers with little elaboration - some use a pnp output transistor however, with its collector connected to chassis.

Circuit Variations:
Variations to the basic circuit commonly found include: transposition of the scan coils and the correction capacitor; connection of the line output transformer primary winding and its e.h.t. overwinding in series; connection of the deflection components to a tap on the transformer to obtain correct matching of the components and conditions in the stage; use of a boost diode which operates in identical manner to the arrangement used in valve line output stages, thereby increasing the effective supply to the stage; omission of the efficiency diode where the stage is operated from an h.t. line, the collector -base junction of the line output transistor then providing the efficiency diode action without, in doing so, producing scan distortion; addition of inductors to provide linearity and width adjustment; use of a pair of series -connected line output transistors in some large -screen colour chassis; and in colour sets the addition of line convergence circuitry which is normally connected in series between the line scan coils and chassis. These variations on the basic circuit do not alter the basic mode of operation however.

Resonance
The most important fact to appreciate about the circuit is that when the transistor and diode are cut off during the flyback period - when the beam is being rapidly returned from the right-hand side of the screen to the left-hand side the tuning capacitor together with the scan coils and the primary winding of the line output transformer form a parallel resonant circuit: the equivalent circuit is shown in Fig. 1(b). The line output transformer primary winding and the tuning capacitor as drawn in Fig. 1(a) may look like a series tuned circuit, but from the signal point of view the end of the transformer primary winding connected to the power supply is earthy, giving the equivalent arrangement shown in Fig. 1(b).

The Flyback Period:
Since the operation of the circuit depends mainly upon what happens during the line flyback period, the simplest point at which to break into the scanning cycle is at the end of the forward scan, i.e. with the beam deflected to the right-hand side of the screen, see Fig. 2. At this point the line output transistor is suddenly switched off by the squarewave drive applied to its base. Prior to this action a linearly increasing current has been flowing in the line output transformer primary winding and the scan coils, and as a result magnetic fields have been built up around these components. When the transistor is switched off these fields collapse, maintaining a flow of current which rapidly decays to zero and returns the beam to the centre of the screen. This flow of current charges the tuning capacitor, and the voltage at A rises to a high positive value - of the order of 1- 2k V in large -screen sets, 200V in the case of mains/battery portable sets. The energy in the circuit is now stored in the tuning capacitor which next discharges, reversing the flow of current in the circuit with the result that the beam is rapidly deflected to the left-hand side of the screen - see Fig. 3. When the tuning capacitor has discharged, the voltage at A has fallen to zero and the circuit energy is once more stored in the form of magnetic fields around the inductive components. One half -cycle of oscillation has occurred, and the flyback is complete.

Energy Recovery:
First Part of Forward Scan The circuit then tries to continue the cycle of oscillation, i.e. the magnetic fields again collapse, maintaining a current flow which this time would charge the tuning capacitor negatively (upper plate). When the voltage at A reaches about -0.6V however the efficiency diode becomes forward biased and switches on. This damps the circuit, preventing further oscillation, but the magnetic fields continue to collapse and in doing so produce a linearly decaying current flow which provides the first part of the forward scan, the beam returning towards the centre of the screen - see Fig. 4. The diode shorts out the tuning capacitor but the scan correction capacitor charges during this period, its right-hand plate becoming positive with respect to its left-hand plate, i.e. point A. Completion of Forward Scan When the current falls to zero, the diode will switch off. Shortly before this state of affairs is reached however the transistor is switched on. In practice this is usually about a third of the way through the scan. The squarewave applied to its base drives it rapidly to saturation, clamping the voltage at point A at a small positive value - the collector emitter saturation voltage of the transistor. Current now flows via the transistor and the primary winding of the line output transformer, the scan correction capacitor discharges, and the resultant flow of current in the line scan coils drives the beam to the right-hand side of the screen see Fig. 5.

Efficiency:
The transistor is then cut off again, to give the flyback, and the cycle of events recurs. The efficiency of the circuit is high since there is negligible resistance present. Energy is fed into the circuit in the form of the magnetic fields that build up when the output transistor is switched on. This action connects the line output transformer primary winding across the supply, and as a result a linearly increasing current flows through it. Since the width is
dependent on the supply voltage, this must be stabilised.

Harmonic Tuning:
There is another oscillatory action in the circuit during the flyback period. The considerable leakage inductance between the primary and the e.h.t. windings of the line output transformer, and the appreciable self -capacitance present, form a tuned circuit which is shocked into oscillation by the flyback pulse. Unless this oscillation is controlled, it will continue into and modulate the scan. The technique used to overcome this effect is to tune the leakage inductance and the associated capacitance to an odd harmonic of the line flyback oscillation frequency. By doing this the oscillatory actions present at the beginning of the scan cancel. Either third or fifth harmonic tuning is used. Third harmonic tuning also has the effect of increasing the amplitude of the e.h.t. pulse, and is generally used where a half -wave e.h.t. rectifier is employed. Fifth harmonic tuning results in a flat-topped e.h.t. pulse, giving improved e.h.t. regulation, and is generally used where an e.h.t. tripler is employed to produce the e.h.t. The tuning is mainly built into the line output transformer, though an external variable inductance is commonly found in colour chassis so that the tuning can be adjusted. With a following post I will go into the subject of modern TV line timebases in greater detail with other models and technology shown here at  Obsolete Technology Tellye !


- The EHT Output is realized with a selenium rectifier.

The EHT selenium rectifier which is a Specially designed selenium rectifiers were once widely used as EHT rectifiers in television sets and photocopiers. A layer of selenium was applied to a sheet of soft iron foil, and thousands of tiny discs (typically 2mm diameter) were punched out of this and assembled as "stacks" inside ceramic tubes. Rectifiers capable of supplying tens of thousands of volts could be made this way. Their internal resistance was extremely high, but most EHT applications only required a few hundred microamps at most, so this was not normally an issue. With the development of inexpensive high voltage silicon rectifiers, this technology has fallen into disuse.

VOXSON T1741 CHASSIS 3.55 Tuning unit with bandswitch for high frequency receivers

Abstract:

A tuning unit with a bandswitch for high frequency receivers having a potentiometer system for the control of capacity diodes is disclosed. The potentiometer system includes a plurality of parallelly disposed resistance paths on which wipers can be moved by means of screw tuning spindles mounted beside one another in a common housing made of an insulating material. The bandswitch is formed of metal wires and is associated with each tuning spindle. The tuning spindles are joined for rotation with sleeves simultaneously forming the operating knobs which are carried in apertures in the front plate and each have a flange engaging the back side of the front plate about the apertures. The flange is slightly larger than the cross section of the apertures and tapers conically away from the back side of the front plate.

1. Tuning unit with bandswitch for high frequency receivers having potentiometer means for the control of capacity diodes composed of a plurality of parallelly disposed resistance paths on which wipers are moved by means of screw tuning spindle means mounted beside one another in a common housing of insulating material, bandswitch means formed of metal wires associated with each tuning spindle means, said tuning spindle means being joined for rotation with sleeve means simultaneously forming operating knobs which are borne in apertures in the front plate and each sleeve means having an axial flange surface engaging the back side of the front plate about one aperture therein, said flange surface being slightly larger than the cross section of the apertures and tapering conically away from the back side of the front plate.

2. Tuning unit of claim 1 wherein the sleeve means are joined telescopically and coaxially with the tuning spindle means, and the flange surface engages the back side of the front plate when the sleeve means are in the state wherein they are pulled out of the front plate.

3. Tuning unit of claim 1 wherein the ends of the tuning spindle means which are opposite the front plate have each an annular groove into which a spring bracket engages whose bent end is supported against the housing and which has two diametrically disposed spring arms having opposite spring curvature, the said spring arms in each case contacting the opposite axial walls of the groove.

4. Tuning unit of claim 3 wherein the spring bracket rests with its bent end against the housing and the spring arms additionally engage a bracket formed on the housing or an intermediate bracket formed in one piece with the connection soldering lugs.

5. Tuning unit of claim 3 wherein the spring bracket is formed in one piece with the connection soldering lugs and has spring arms curved both in the same direction which engage an axial wall of the annular groove in the spindle and the opposite axial wall rests against a housing wall.

6. Tuning unit of claim 1 wherein the pointers associated with each potentiometer means lie on the one hand in windows associated with each tuning spindle means in the front plate, and on the other hand are rotatably mounted with their ends opposite the front plate in pivot pins on the housing, and the guiding pin of the spindle nuts carried in a longitudinally displaceable manner on each tuning spindle is provided with a slit disposed parallel to the longitudinal axis of the tuning spindle and slides with its peripheral surface resiliently within the slide tract of the pointer.

7. Tuning unit of claim 1 wherein the bandswitches are formed each of a displaceable metal rod which is in working engagement with stationary metal rods common to all bandswitches of a tuning unit, contacting each of them individually.

8. Tuning unit of claim 7 wherein the metal rods are metal wires.

9. Tuning unit of claim 7 wherein the metal rods are stamped metal parts.

10. Tuning unit of claim 7 wherein levers of insulating material are placed on the front ends of the displaceable metal rods and extend through windows which are provided with detents and which are associated with each tuning spindle in the housing front plate, while the opposite ends are held fixedly in the rearward end of the housing, and the displaceable metal rods individually make contact with contact cams on the stationary metal rods, these cams being in an offset array corresponding to the detents in the windows, the corresponding rods extending parallel to the front plate and parallel to one another behind the front plate.

11. Tuning unit of claim 7 wherein insulating material bridges or insulating material slide pieces are inserted between the contact cams of two adjacent, stationary metal rods and within the free space between two such parallel metal rods.

12. Tuning unit of claim 7 wherein the displaceable metal rods have, in the vicinity of their mountings on the housing, an articulation in the form of a vertically disposed flat portion.

Description:

BACKGROUND

The invention relates to a tuning unit with bandswitch for high frequency receivers, especially radio and television receivers, having a potentiometer system for the control of capacity diodes, the said potentiometer system consisting of a plurality of parallel resistance paths along which wiper contacts can be driven by means of screw spindles disposed adjacent one another in a common insulating material housing in which a bandswitch formed of metal rods is associated with each tuning spindle.
In these tuning units, the working voltages of the capacity diodes in the tuning circuits are recorded once a precise tuning to the desired frequency has been performed. A potentiometer tuning system has great advantages over the formerly used channel selectors operating with mechanically adjustable capacitors (tuning condensers) or mechanically adjustable inductances (variometers), mainly because it is not required to have such great precision in its tuning mechanism.
Tuning units with bandswitches formed of variable resistances and combined with interlocking pushbuttons controlling the supply of recorded working voltages to capacity diodes are known. Channel selection is accomplished by depressing the knobs, and the tuning or fine tuning are performed by turning the knobs. The resistances serving as voltage dividers in these tuning units are combined into a component unit such that they are in the form of a ladderlike pattern on a common insulating plate forming the cover of the housing in which the tuning spindles and wiper contacts corresponding to the variable resistances are housed. The number of resistances corresponds to the number of channels or frequencies which are to be recorded. The wiper contact picks up a voltage which, when applied to the capacity diodes determines their capacitance and hence the frequency of the corresponding oscillating circuit. The adjustment of the wipers is performed by turning the tuning spindle coupled to the tuning knob. By the depression of a button the electrical connection between a contact rod and a tuning spindle is brought about and thus the selected voltage is applied to the capacity diodes. Since the push buttons release one another, it is possible simply by depressing another button to tune to a different receiving frequency or a different channel, as the case may be.
To permit the switching of a number of channels in a certain tuning range, bandswitches for a plurality of tuning ranges, such as UHF and VHF for example, are often provided in the tuning units described above. In the pushbutton tuning unit of the above-named type, the bandswitch consists of a printed circuit board which is fastened on the housing of the tuning unit, and a switch lever which is preset by means of the pushbutton by turning, and is operated by depressing the pushbutton while at the same time selecting the channel.
Where this combination of knobs and pushbuttons is not possible, the selection of the range is accomplished by means of an additional lever which can be set over to select the range.
However, since such tuning units require too many riveting operations when they are assembled, tuning units were later created in which the individual parts in the voltage divider and pushbutton housing were loosely inserted and/or held in place by projections, lugs, hooks or tabs of resilient plastic. In spite of these initial improvements, the bandswitch, especially the one associated with the tuning units, was still technically intricate and very expensive.
THE INVENTION
It is the object of the invention, therefore, to create an additionally improved and simplified tuning unit containing a bandswitch of simple, space-saving and reliably operating design.
In accordance with the invention, this object is accomplished in a tuning unit with bandswitch of the kind described in the beginning by joining the tuning spindles for rotation with sleeves simultaneously forming the control knobs, which are mounted in apertures in the front plate of the housing and have each a flange engaging the back of the front plate around the aperture, the said flange being slightly larger than the aperture and tapering conically away from the back of the front plate.

In further development, the sleeves can be joined telescopically for rotation with the tuning spindles, and the flange is able to engage the back side of the front plate when the sleeve is in the position in which it is drawn out of the front plate. The sleeves constructed in this manner, whose portions projecting from the apertures in the front plate form the control knobs for the tuning spindles, permit easy assembly of the tuning unit and at the same time assure positive co-rotation of sleeves and spindles. The sleeves can be pushed from the front side of the front plate through the apertures onto the clutch surfaces of the spindles, this inward pushing being easily accomplished on account of the taper, and the dropping out of the sleeve being prevented by the flange engaging the back of the front plate. If the control knobs project only slightly out of the front plate, they can be operated from the outside by inserting a tool into them. With the telescoping type of coupling, however, it is possible to draw the sleeves or control knobs further outwardly so that they can be rotated by hand without the use of tools.
To provide constant assurance of the axial fixation of the tuning spindles, the tuning spindle ends farthest from the front plate can each be provided with an annular groove engaged by a spring bracket whose one leg is supported against the housing and whose other leg is forked to form two spring arms, each bent in the opposite direction and each engaging one of the two opposite walls of the annular groove. The tuning spindles are secured against axial displacement by this construction of the invention alone, without the need for further measures. This facilitates the joining of the sleeves or control knobs to the tuning spindle, because in this case there is no need for precise axial fixation and extreme dimensional accuracy.

Furthermore, the indicators associated with each potentiometer can be mounted in windows in the front plate which are associated with each tuning spindle or tuning knob for visual indication at the front, the other extremities farthest from the front plate being mounted for pivoting on pins set in the housing; the guiding pin on the spindle nut that is driven longitudinally on each tuning spindle can be provided with a slit disposed parallel to the long axis of the tuning spindles and can slide within the indicator slide lever slot, with its surface resiliently engaging the walls of said slot.
In an especially advantageous embodiment, the tuning unit can have bandswitches each formed of a displaceable metal rod which is in contacting engagement individually with stationary metal rods which are common to all of the bandswitches of a tuning unit. It contrast to the bandswitches known hitherto, which as a rule consist of a printed circuit board with switchable contacts thereon, this frequency bandswitch of the invention is of great simplicity, can be manufactured simply and inexpensively, and at the same time is very reliable in operation.
The displaceable and stationary metal rods of the bandswitches can be formed of metal wires or they can be of stamped sheet metal. Also, in further expansion of the concept of the invention, the stationary metal rods thus formed can be all entirely alike and merely offset from one another, thereby further simplifying the manufacture and stocking thereof.
To permit connection also to audiovisual apparatus, one or more of the stationary metal rods can be divided electrically into at least two parts each.
In a special development of this concept, lugs of insulating material can be mounted on the front ends of the displaceable metal wires, these lugs extending through windows in the front plate of the housing which are associated with each tuning spindle and are provided with detents, while the opposite ends can be held fixedly at the rear end of the housing, and the displaceable metal wires can make contact with contact humps on the stationary metal wires, the humps being offset from one another to correspond to the detents in the windows, and the stationary metal wires extending in back of the front plate, parallel to the latter and parallel to one another.
To increase switching reliability, bridges or sliding pieces made of insulating material can be inserted between the contact humps of adjacent stationary wires within the free space between two such parallel lying metal wires.
To achieve easy displacement of the displaceable metal wires despite the fixed end mounting on the housing, the displaceable metal wires, in further embodiment of the invention, can have each an articulation adjacent their end mountings, in the form of a vertically disposed flattened portion. This flat permits the metal wires to be deflected horizontally against a weak spring bias.
DESCRIPTION OF THE DRAWING
As an example of the embodiment of the invention, there is represented in the drawings a tuning unit with bandswitch for television receivers. In these drawings,
FIG. 1 is a front elevational view of a tuning unit with bandswitch,
FIG. 2 is a plan view showing the bandswitch of the tuning unit of FIG. 1,
FIG. 3 is a side elevational, cross-sectional view of the tuning unit of FIG. 1,
FIG. 4 is a rear elevational view of the tuning unit of FIG. 1,
FIG. 5 is a plan view showing the indicator means of the tuning unit of FIG. 1,
FIG. 6 shows the sleeve with the operating knob and tuning spindle,
FIG. 7 shows the telescoping manner in which the sleeve is joined to the tuning spindle,
FIG. 8 is a fragmentary view of the bandswitch,
FIG. 9 is another fragmentary view of the bandswitch, and
FIG. 10 shows how the tuning spindle is fixed in position.
DESCRIPTION
The method of representation used in the drawings is greatly simplified, for the purpose of better delineating the features of the invention. The tuning unit with bandswitch consists of an insulating material housing 1 with a front plate 2, which is closed by a cover plate 3 accommodating the resistance paths. The housing 1 is divided by parallel sidewalls 4 into chambers in which the tuning spindles 5 are disposed.
The embodiments is an 8-fold tuning unit having eight bandswitches assocated with each tuning spindle, and eight indicators.
Accordingly, there are eight apertures 6 in a central row, through which the operating knobs 7 of the sleeves 8 coupled with the tuning spindles 5 are passed. The operating knobs 7 have recessed surfaces 9 for turning with a turning tool. In a row extending parallel above the row of the apertures 6 there are eight windows 10, whose upper edge is provided with notches 11. Lugs 12 of insulating material extend through the windows 10 and engage the upper notches 11 and are joined behind the front plate to displaceable metal wires 13 of the bandswitch. In a row located beneath the row of apertures 6 another eight windows 14 are provided, through which the ends of the pointers of the indicators 15 protrude.
Now, the bandswitch consists in each case of a displaceable metal wire 13 which can be brought into working engagement with stationary metal wires 16, which are all of the same construction and are only disposed offset from one another. While the displaceable metal wire 13 extends substantially parallel to the longitudinal axis and thus at right angles to the front plate 2, the stationary, parallelly disposed metal wires 16 are parallel to the front plate 2 and are thus inserted at a right angle to the displaceable metal wire. A departure from parallelism or from the right angle, as the case may be, takes place substantially only when the displaceable metal wire 13 is deflected to the two outer notches. The rearward end 18 of the displaceable metal wire, which forms a vertical loop, is tightly inserted into a receiver 17. Just ahead of the loop 18, the metal wire 13 is provided with a vertically disposed portion 19 by a flattening on the metal wire 13. The movement, when the metal wire 13 is deflected into the desired notches or detents, takes place horizontally by the flexing of these portions 19. The stationary metal wires 16 are held tightly in their positions in projections 20 on the housing, or by lugs or the like. Since three switch actions are provided, that is, three ranges, for each tuning spindle, a bandswitch consists of one displaceable metal wire and three stationary metal wires 16, which are used for all switches.
To permit each bandswitch to have exactly three switching actions, each of the three stationary metal wires 16 has one contact hump 21 corresponding to one of the detents 11 in the windows 10 of the front plate 2. The contact humps 21 are thus located one next to the other as seen from the front plate 2. So that the displaceable metal wire 13 will always come into mechanical and electrical contact only with the desired contact hump, and prevent short circuits, insulating bridges 22 are installed between the adjacent metal wires 16, said insulating bridges being stationary.
If more or less than three switching actions are desired, all that need be done in the case of the bandswitch of the invention is to change the number of stationary metal rods or wires accordingly.
The sleeves 8 with the operating knob 7 have a flange 23 engaging the back of the front plate 2 and tapering back to the point where it joins the tuning spindle. This enables the sleeves to be pushed in, in the case of a housing that has already been manufactured with the tuning spindle installed, without creating the possibility that the sleeves 8 might escape after they have been inserted. The sleeves 8 are connected to the tuning spindles 5 usually by means of driving surfaces. If manual operation without tools is to be possible, rather than requiring a tool for the operation of the sleeves, the coupling of the sleeve 8 to the tuning spindle will be a telescoping coupling (see FIG. 7).
The actual firm axial fixation of the tuning spindle 5 is located on the rear end of the housing. Here the tuning spindle 5 has an annular groove 24 which is engaged by a spring by means of two diametrically disposed spring arms 25 and 26. The spring arms 25 and 26 have oppositely curved lugs and are supported on the housing at their terminal and marginal surfaces and their lugs engage opposite axial walls 27 and 28 of the annular groove 24.
Additional support is provided by the common, bent foot 29 of the spring arms 25 and 26 against the cover plate of the housing.
The indicator means of the tuning unit with bandswitch consists of a pointer 15 which is movable within the window 14, and a cam 30 which is a prolongation of the pointer 15. At its rearward end, the pointer is mounted rotatably in the housing on pin 31. Within the cam 30 slides a guiding pin 32 which is attached to the spindle nut or carriage 40. Upon the rotation of the tuning spindle, the spindle nut is longitudinally displaceable therewith. In order to achieve good guidance and hence precise indication, the guiding pin has a slit 33 extending parallel to the longitudinal axis of the tuning spindle 5, so that it will resiliently engage the cam 30 within the slot thereof.
The necessary soldering lugs are indicated at 34.
On the basis of the design of the tuning unit with bandswitch in accordance with the invention, a desired frequency range--UHF, for example--can be selected by deflecting a displaceable metal wire 13 into one of the detents 11 by means of the lug 12 mounted thereon. Within this range, a transmitter or channel can then be selected by turning the tuning spindle 5. The transmitter preselected in this manner can then be tuned in by means of a keyboard or by electronic recall from a keyboard which is not shown. The fine tuning of this tuned-in transmitter, as well as the selection of a different transmitter within the same frequency range, is accomplished by turning the tuning spindle 5.
All of the details explained in the above description and represented in the drawings are important to the invention.

VOXSON T1741 CHASSIS 3.55 CRT TUBE PHILIPS A44-510W.

CRT TUBE PHILIPS  A44-510W.

 1. INTRODUCTION
Equipment design should be based on the characteristics as stated in the data sheets. Where deviations from these general recommendations are permissible or nec- essary, sta~ements to that effect will be made. If applications are considered not referred to in the data sheets of the relevant tube type extra care should be taken with circuit design to avoid that the tube is overloaded due to unfavourable operating conditions.


2. SPREAD IN TUBE CHARACTERISTICS
The spread in tube characteristics is the difference between maximum and min- imum 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 dif- fering from those specified in the data sheets. .


3. SPREAD AND VARIATION IN OPERATING CONDITIONS
The operating conditions of a tube are subject to spread and/or variation. 3. 1 Spread. Spread in an operating condition is a permanent deviation from an av- eragecondition due to, e.g. ,component value deviations. The average condition is found from such a number individual cases taken at random that a;. increase of the number will have a negligible influence. 3.2 Variation. 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 negli- gible influence.

4. LIMITING VALUES
4. 1 Limiting values are in accordance with the applicable rating system as defined by I.E.C. publication 134.


Reference may be made to one of the following 3 rating systems.
4. 1. 1 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.

4.1.24.
1.Note*.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 conditions with respect to supply voltage variation, equipment components spread and variation, equip- ment 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 val- ues 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 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 characteristics of the elec- tronic device under consideration. The equipment manufacturer should design so that, initially and throughout life, no design -maximum value for the intended service is exceeded 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 adjust- ment, load variation, signal variation and environmental conditions. 3Design-centre rating system. Design -centre ratings are limiting values of operating and environmental conditions applicable to a bogey electronic de- vice* 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. 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 ob- tained by considering only those characteristics which are directly related
to the application.

4.2 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 .

4.3 In addition to the limiting values given in the individual data sheets the direc- tives in the following paragraphs should be observed.

5. HEATER CIRCUIT
Any deviation from the nominal heater voltage (in case of parallel connection) or from the nominal heater current (in case of series connection) has a detrimental effect on tube performance and life, and should therefore be kept at a minimum.
Such deviations may be caused by:
a) Mains voltage fluctuations. b) Spread in the characteristics of components such as transformers, resistors capacitors etc. Designers of heater circuits are strongly recommended to bear this in mind when dealingwith equipment to be used in areas where the actual mains voltage is like- ly to differ from the nominal value.

5. 1 Parallel connection
The maximum deviation of the heater voltage should not exceed ± 15~ (design maximum value). This conditionwill be fulfilled when the mains voltage fluctuates by ± 10~ and a ordinary transformer (see below) is used.

5.2 Series connection
The maximum deviation of the heater current should not exceed ± 8~ (design maximum value). When a small number of tubes with large differences in the heater voltage is used in series connection combined with a series resistor or a series capacitor, the maximum permitted deviation of the heater current may be exceeded. To avoid this, certain restrictions must be imposed on the composition of the heater chain; the maximum part of the supply voltage that can be eliminated, and the tolerances of the voltage dropper in series with the heaters. A number of circu.'.ts for If = 300 mA will be described in detail below.

CATHODE TO HEATER VOLTAGE
The voltage between cathode and heater should be as low as possible and never exceed the limiting value given on the data sheets of the individual tubes. The values given under "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 voltages. Unless other- wise stated, the maximum values quoted for the voltage between cathode and heater indicate the maximum permissible value (D. C. component). If an A.C. voltage, or an combination of D. C, and A.C. voltages. is applied the peak value may be twice the rated Vk{; however. unless otherwise stated, the peak value shall never exceed 31~ V. The D.C. component is not allowed to exceed the pub- lished value. Unless otherwise stated, the V~ max. holds for both polarities of the voltage; however, a positive cathode is usually the most favourable in view of insulation during life. In order to avoid excessive hum the A.C. component of the heater to cathode voltage should be as low as possible and never exceed 20 Vrms (mains frequency).

7. INTERMEDIATE ELECTRODES (between cathode and final accelerator) In no circumstances should the tube be operated without a D.C. connection be- tween each electrode and the cathode. The total effective impedance between each electrode and the cathode should never exceed the published maximum value. However, no electrode should be connected directly to a high energy source such as the hot line. When such a connection is required, it should be made via a se- ries resistor of not less then 1 kohm

.8. ELECTRODE VOLTAGES
All electrode voltages are given with respect to cathode.
For cathode drive service the reference point is grid No.l

8. 1 Grid No.l cut-off voltage
Generally curves showing the limits of grid No. 1 cut-off voltage for specific values of the first accelerator voltage are included in the data. The brightness control should be so dimensioned that it can handle any tube within the limits shown, at the appropriate first accelerator voltage. The published limits are determined at an ambient illumination level of 10 lux with the aid of a focused raster. Because the brightness of a focused spot is in general greater than that of a raster, the visual cut-off voltage determined with the aid of a spot will be more negative by about 5 V.

8.2 Grid No.2 voltage
For each individual tube the grid No.2 voltage can be adjusted so that the beam current is cut off at a fixed value within the published range of the grid No.l voltage . In the data, graphs are included giving the relationship between. the grid No.2 voltage and the grid No. 1 cut-off voltage. ~8.3 Focusing electrode voltage Individual tubes will have satisfactory focus over the entire screen at some value within the published range of the focusing voltage. If centre -focusing is desired this range will shift in the negative direction.

9. LUMINESCENT SCREEN
To prevent permanent damage to the screen material care should be taken
a. not to operate the tube with a stationary picture at high beam currents for ex- tended periods
b. not to operate the tube with a stationary or slowly moving spot except at ex- tremely low beam currents
c. to choose the time constants of the grid No. 1 the grid No.2 and the time bases supply line circuits such that sufficient beam current is maintained to dis- charge the e. h. t. capacitance before deflection has ceased after equipment has been switched off.

10. EXTERNAL CONDUCTIVE COATING
The external conductive coating must be connected to the chassis. The capac- itance 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 radiation caused by the line time base it may be necessary to make multiple connections to the coating. See also 12.

To centre the raster on the screen it is recommended that either a magnetic field just behind the deflection coils (viewed from the screen) be used or a direct current be passed through the deflection coils. The centring device should provide a shift to allow for non-centrality of the spot with respect to the geometric centre of the screen, in addition the centring device should provide the shift needed to allow for non -centrality of the visible raster (i. e. to compensate for line blanking and also time base non-linearity, if any) andtheearth magnetic field. The use of a too strong centring magnetic field should be avoided; this may result in raster distortion and even corner cutting.

PRO-ELECTRON TYPE DESIGNATION CODE
Single letter, group of figures, hyphen, group of figures, letter or letter group. The first letter indicates the prime application of the tube:

A -Television display tube for domestic application.
M -Television display tube for professional application-direct view.

First group of figures: Diameter or diagonal of the face in cm. Second group of figures: Development or design number. Final letter or letter group: Properties of the phosphor screen. The first letter denotes the colour of the fluorescence, the second letter, if any,other specific differences in screen properties.

W -White screen for T '~ display tubes.
X - Three-colour screen for T.V. display tubes.