EMERSON VULCAN 24" YEAR 1973

 

The EMERSON  VULCAN 24"  is a 24 (61 cm) B/W television with 6 VHF/UHF  programs keyboard selected channels and tuning potentiometers drawbar side right located for every single program.

ALL commands are manual perfomed with knobs and rotatable knobs for Volume, Brightness, Contrast and On/OFF switch.

• The set is first EMERSON B/W big screen entirely featured with semiconductors and units in modular fashion. 

 

 The mechanical turret approach to television tuning has been used almost exclusively for the past over  60 years. Even though replete with the inherent disadvantages of mechanical complexity, unreliability and cost, such apparatus has been technically capable of performing its intended function and as a result the consumer has had to bear the burdens associated with the device. However, with the " recent " Broadcast demands for parity of tuning for UHF and VHF channels, the increasing number of UHF and cable TV stations have imposed new tuning performance requirements which severely tax the capability of the mechanical turret tuner. Consequently, attempts are now being made to provide all electronic tuning to meet the new requirements.

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.

 Moreover, using this arrangement, the only indication--during adjustment--of which channel is selected is by station identification.

• The set is build with a Modular chassis design because as modern television receivers become more complex the problem of repairing the receiver becomes more difficult. As the number of components used in the television receiver increases the susceptibility to breakdown increases and it becomes more difficult to replace defective components as they are more closely spaced. The problem has become even more complicated with the increasing number of color television receivers in use. A color television receiver has a larger number of circuits of a higher degree of complexity than the black and white receiver and further a more highly trained serviceman is required to properly service the color television receiver.

Fortunately for the service problem to date, most failures occur in the vacuum tubes used in the television receivers. A faulty or inoperative vacuum tube is relatively easy to find and replace. However, where the television receiver malfunction is caused by the failure of other components, such as resistors, capacitors or inductors, it is harder to isolate the defective component and a higher degree of skill on the part of the serviceman is required.
Even with the great majority of the color television receiver malfunctions being of the "easy to find and repair" type proper servicing of color sets has been difficult to obtain due to the shortage of trained serviceman.
At the present time advances in the state of the semiconductor art have led to the increasing use of transistors in color television receivers. The receiver described in this application has only two tubes, the picture tube and the high voltage rectifier tube, all the other active components in the receiver being semiconductors.
One important characteristic of a semiconductor device is its extreme reliability in comparison with the vacuum tube. The number of transistor and integrated circuit failures in the television receiver will be very low in comparison with the failures of other components, the reverse of what is true in present day color television receivers. Thus most failures in future television receivers will be of the hard to service type and will require more highly qualified servicemen.
The primary symptoms of a television receiver malfunction are shown on the picture tube of the television receiver while the components causing the malfunction are located within the cabinet. Also many adjustments to the receiver require the serviceman to observe the screen. Thus the serviceman must use unsatisfactory mirror arrangements to remove the electronic chassis from the cabinet, usually a very difficult task. Further many components are "buried" in a maze of circuitry and other components so that they are difficult to remove and replace without damage to other components in the receiver.
Repairing a modern color television receiver often requires that the receiver be removed from the home and carried to a repair shop where it may remain for many weeks. This is an expensive undertaking since most receivers are bulky and heavy enough to require at least two persons to carry them. Further, two trips must be made to the home, one to pick up the receiver and one to deliver it. For these reasons, the cost of maintaining the color television receiver in operating condition often exceeds the initial cost of the receiver and is an important factor in determining whether a receiver will be purchased.
Therefore, the object of this invention is to provide a transistorized color television receiver in which the main electronic chassis is easily accessible for maintenance and adjustment. Another object of this invention is to provide a transistorized color television receiver in which the electronic circuits are divided into a plurality of modules with the modules easily removable for service and maintenance. The main electronic chassis is slidably mounted within the cabinet so that it may be withdrawn, in the same manner as a drawer, to expose the electronic circuitry therein for maintenance and adjustment from the rear closure panel after easy removal. Another aspect is the capability to be serviced at eventually the home of the owner.

• This TV chassis was even fitted in other models and was produced for a few as the interests concentrated in Color Tvs.
  

• The set is fabricated in Firenze (Italy) by Giovanni BORGHI EMERSON Firm which activity  was after acquired by Guido BORGHI son of  Giovanni BORGHI.In 1973, his father entrusted him with the management of Emerson, the television manufacturer, of which he became president. The company, in which the Japanese Sanyo had entered after , subsequently due to conflicts between Guido Borghi and the Japanese partners went into crisis and was placed in liquidation in 1980.

 

 Emerson History:

• Emerson Electronics S.p.A., better known as Emerson, was an Italian manufacturer of consumer electronics based in Florence.

The origins of the company date back to 1929, when on the initiative of Mr. Aldobrando Saccardi the sole proprietorship Saccardi Radio was founded in Florence, with headquarters in via Porta Rossa 39/r, which began its activities as the exclusive Radiotelefunken agent, as a concessionaire and repairer of other brands (Phonola, Magnadyne, Geloso, etc.) and with the handcrafted construction of small tube radios.

In March 1950, another shareholder, Dr. Cesare Campagnano, joined Saccardi's company and, transformed into SICART, began a collaboration with the American Emerson Radio & Phonograph Corp. SICART, with headquarters in viale Fratelli Rosselli 61, Emerson licensee and its exclusive distributor for Italy, marketed radios and televisions (assembled with frames imported from the United States) with the homonymous brand produced by the Gold Plated company Fabbriche Riunite of Casalmaggiore, in the province of Cremona. From the 1960s until its closure, SICART would later house Europhon's assistance and sales.

In 1956, the company was transformed into a joint-stock company and assumed the company name Emerson Electronics S.p.A.. The independent industrial activities were subsequently started by the American parent company, with the production of radios, televisions, record players and various electronic components, which initially amounted to 60 -70 prices per day, and the headquarters changed several times until it was located in via Bardazzi, in the Novoli area. The company had flourishing moments around 1961-63, and in 1968, it bought the use of the Emerson brand from the American house and leased the other DuMont brand.

In 1969, Campagnano, holder of 49% of the shares of Emerson, sold the same to the Milanese entrepreneur Giovanni Borghi. Borghi, the following year, in 1970, also took over the shares held by Saccardi, with whom disagreements had arisen regarding the construction of a second production plant. Emerson, under Borghi's ownership, grew both in economic-financial and productive terms, and in terms of employees, thus becoming one of the main Italian companies in the electronics sector: in 1972, together with Geloso of Milan and IREL of Genoa, it formed a consortium called Fabbriche Italiane Riunite Elettroniche e Meccaniche (FIREM), based in the Ligurian capital, and chaired by Borghi. The following year, in 1973, he left the position of president of Emerson to entrust it to his son Guido.

The growth in the turnover of the Tuscan company was remarkable, which went from about 8 billion lire in 1973 to almost 50 billion in 1978, in contrast with the other national companies in the sector, which starting from the second half of the seventies difficulties due to declines in turnover and contraction of market shares. The contraction of market shares was mainly due to the introduction of color television in Italy which took place late compared to other European countries, which prevented the ability to build the prearranged devices: in In this context, Emerson distinguished itself by starting the production of color televisions as early as 1974.

In 1977, the new factory built in Siena, in the Isola d'Arbia area, was inaugurated, a modern plant for the production of color televisions, which employed about 550 people, in addition to the 130 employed in the Florentine factory.


In 1978, a financial crisis loomed which ended with the entry of a new shareholder, the Japanese multinational Sanyo, which acquired 34% of the capital.
  Through this operation, Emerson acquired new technologies and started integrated productions with Sanyo frames and its own aesthetics, while for Sanyo the aim was to facilitate the entry of its products into the European market.

The entry of the new foreign shareholder led to Emerson's marketing of computers and high-fidelity stereophonic systems under its own brand, produced by Sanyo and destined for the Italian and European markets.

The cooperation between Emerson and Sanyo was short-lived, as many misunderstandings arose between the two partners and this situation plunged the company into a serious crisis: in 1980, the Tuscan company accumulated losses of 5 billion lire, reached liquidation at the end of the same year with an attempt at an arrangement with creditors to reduce debts and avoid bankruptcy, and then it was placed in receivership.

While the liquidation and the arrangement with creditors continued, Nuova Emerson S.p.A. was set up. which attempted a relaunch, proposing an association with Indesit and Voxson, and subsequently attempting to enter REL, the national plan for the restructuring of companies in the electronic sector established in 1982 by the Ministry of Industry, from which it was excluded.

In 1985 there was interest from another Japanese electronics giant, Pioneer, to buy the Tuscan company's brand and factories, which however did not lead to anything concrete.

The Siena plant and the Emerson brand were taken over in 1988 by Ultravox Siena, a subsidiary of the Milanese Ultravox and REL.
This company was active until 1999, when it had to close due to bankruptcy, and subsequently the plant passed to a newco controlled by the German Galaxis Holding GmbH which continued the activity, Galaxis Produzione S.p.A., which in turn went bankrupt in 2001


Emerson Electronics S.p.A., a company with registered office in Florence, and two production plants in Florence and Siena, manufactured Emerson brand televisions and marketed other types of products under the same name, such as video recorders, hi-fi systems and calculators.
In 1979, the company had 836 employees in the two plants, and achieved a turnover of 57.5 billion lire and an operating loss of 58 million.
In the television market, Emerson was fourth in Italy after Philips, Grundig and Telefunken, and the sale of such products constituted 90% of its turnover.
 20% of television sales were made abroad, most of them in West Germany.
Sponsorships
Emerson was a sponsor of Pallacanestro Varese in the 1978-79 and 1979-80 seasons.

  The Milan industrialist Giovanni Borghi founded the IGNIS brand of household appliances.  His factories would turn out one appliance every eight seconds, and make billions selling them to Italy's exploding middle class.   Borghi was famous for his early support of cycling, and his yellow IGNIS jerseyed squadra won more than a few great races in the late fifties and early sixties.

Borghi was aggressive, flamboyant and flashy.  And he took care of his stars - famously buying Spanish sprinter Miguel Poblet a Lancia convertible after his Milan San Remo win.   On top of his 25 million lire per year salary.  

Giovanni Borghi, was an Italian industrialist pioneer in the field of domestic appliances, returned from a trip in the USA with a real
illumination: refrigerators insulated with Polyurethane foam were much more
efficient and capacious than those hand-filled with mineral wood.
His refrigerators Group, Ignis, developed internally this technology and the
related equipment, a suitable alternative to the imported foam dispensers, which
were difficult to get, fix and maintain, stimulating an industrial supply of
similar machines.  

 And in 1959 Borghi signed the man most of Italy thought would be the man to replace Fausto Coppi:  1956 Olympic, 1958 Giro d'Italia and World Champion  Ercole Baldini.  He lured Baldini away from Legnano with a contract so fat many said it only served to asurre that il treno di Forli.. would...well...get a little too fat himself!  He was never quite as hungry once he went to IGNIS.

Borghi kept control of IGNIS in the family.  In the paternalistic Italian industrial model - like Ferrari, Maserati or Campagnolo.   He later turned the reins over to his son, who in turn finally sold the company to Dutch conglomerate, Philips.
 
When Philips decided to get into the major household appliances
market, its procedure was to buy increasing quantities of these goods from the Italian firm, Ignis, then at the height of its prosperity.
Once it became the principal client of the manufacturer, it took over supplying the latter by purchasing 50 percent of its capital. It took over the firm completely in 1972, to the satisfaction of the founder of Ignis, Giovanni Borghi.

In 1988, IRE-Ignis became a joint venture between Philips and Whirlpool, which entered the capital with 53% of the shares, becoming the majority shareholder.

The American company in 1991, acquired the whole of the Ignis, which became Italy s.r.l, Whirlpool and Whirlpool Europe later, and since then is a part of the group, which produced household appliances in the Italian plants, still active
BORGHI DIED IN 1975.
 
Borghi is still remembered in Italia.   RAI even aired TV miniseries about his life this past year, "Mister Ignis". 

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

Further NOTES and readings.

^ ANTICHE DITTE RADIO A FIRENZE, su iw5csj.jimdofree.com. URL consultato il 16 aprile 2021.
^ Ditta Saccardi Firenze, su carlobramantiradio.it. URL consultato il 16 aprile 2021.
^ Inserzione pubblicitaria pubblicata da Emerson Electronics S.p.A. sulla rivista Epoca n. 988 del 31 agosto 1969
^ Annuario industriale della Provincia di Milano, Unione Industriale Fascista della Provincia di Milano, 1933, p. 217.
^ E. Parente, SICART "La Voce del Mondo" mod. 232 radiofonografo, in Antique Radio Magazine, n. 139, Club Antique Radio Magazine, settembre-ottobre 2017, pp. 10-15.
^ Gazzetta Ufficiale del Regno d'Italia, Foglio delle inserzioni n. 20 del 25 gennaio 1936, p. 106
^ Da non confondere con la SICART (Società Italiana Commercio Apparecchi Radio e di Televisione) di Milano, fondata nel 1931, che commercializzava radioricevitori e radiofonografi con il marchio La Voce del Padrone, fino alla sua messa in liquidazione avvenuta nel 1936.^[5][6][7]


Archivio Emerson.
^ XVIII Mostra nazionale della radio e televisione. Elenco degli espositori in L'Antenna n.9 del settembre 1951, p. V
^ Inserzione pubblicitaria della Emerson Radio and Television pubblicata sulla rivista L'Antenna n. 12 del dicembre 1949, p. 536
^ Inserzione pubblicitaria della SICART pubblicata sulla copertina della rivista Radio Industria Televisione n. 177 del settembre 1951
^ B. Cappello, La fabbrica dell’oro matto, in Preziosa Magazine, 29 aprile 2015. URL consultato il 17 aprile 2021.
^ Sentenze e note, in Rivista di diritto industriale, n. 5, Giuffrè, settembre-ottobre 1956, p. 189.
^ Kompass, vol. 2, Etas, 1971, p. 1473.
^ G. Migliorino, Nasce la superazienda elettronica, in Corriere della Sera, 17 ottobre 1972, p. 7.
^ Entra in scena Borghi junior, in Corriere della Sera, 15 dicembre 1973, p. 6.


Emerson in quinta marcia, in Selezione di tecnica. Radio TV HiFi Elettronica, n. 3, JCS, marzo 1979, p. 266.
^ L'Emerson (Borghi) insieme ai giapponesi, in Corriere della Sera, 20 gennaio 1978, p. 27.

20. La Sanyo (giapponese) acquista il 30 per cento della Emerson, in La Stampa, 20 gennaio 1978, p. 16.
21. ^ G. Mazzuca, Forse Sanyo divorzierà da Emerson dopo solo due anni di «matrimonio», in Corriere della Sera, 16 ottobre 1980, p. 12.
22. ^ G. Mazzuca, L'Emerson sarà messa in liquidazione, in Corriere della Sera, 22 ottobre 1980, p. 13.
23. ^ M. Salvatorelli, Nasce in Italia un colosso elettronico, in La Stampa, 21 febbraio 1981, p. 10.
24. ^ I GIAPPONESI DELLA PIONEER INTERVENGONO PER LA EMERSON, in La Repubblica, 28 luglio 1985, p. 30. URL consultato il 17 aprile 2021.
25. ^ Nuovo stabilimento a Siena, in L'Unità, 15 gennaio 1988, p. 12.
26. ^ F. Saulino, DUE MILIARDI A DIPENDENTE PER 'SALVARE' LA EMERSON, in La Repubblica, 6 febbraio 1988, p. 55. URL consultato il 15 aprile 2021.
27. ^ 1898/1999 ULTRAVOX SIENA SPA, su portalecreditori.it. URL consultato il 14 aprile 2021.
28. ^ CONTRATTAZIONE PROVINCIALE SETTORE METALMECCANICO (1991-1998), su archivio.movimentooperaio.com.
29. ^ V. Ravizza, Borghi, l'amico dei giapponesi, in La Stampa, 29 maggio 1980, p. 15.

• R. Delfiol (a cura di), Archivio Emerson (Inventario) (PDF), Firenze, Soprintendenza Archivistica e Bibliografica della Toscana, 2000, nota 1, pp. 3-4.

External LINKS:

• Emerson Electronics; Firenze, su radiomuseum.org. URL consultato il 16 aprile 2021.
• Emerson, su aireradio.org. URL consultato il 16 aprile 2021.

EMERSON VULCAN 24" CHASSIS 50140092 INTERNAL VIEW

 

EMERSON MOD. VULCAN 24"  CHASSIS  50140092

  The CHASSIS TECHNOLOGY is based on ASIC'S which are:here after listed  and lots of discretes.

UNITS:

X5526 LINE OSCILLATOR  AND FRAME OSCILLATOR

X5525 LINE OUT AND EHT OUT AND VIDEO SUPPLY
 
 X5489 I.F. DETECTOR AND AMPLIFIER
 
 X5527 +30VOLT SUPPLY / VIDEO FINAL STAGE AMPL  /  AUDIO OUT AMPLIFIER

ICS:

 
SN7600P VIF AMPLIFIER AND VIF CAG

SN76003 SOUND AMPLIFIER 16 OHM OUT

TBA311  VIDEO AMPLIFIER / SYNCH SEPARATOR FOR LINE AND FRAME DEFLECTIONS / AGC VOLTAGE REG. /FRAME CANCELLATION / NOISE REJECTION  

SN76660P SOUND PREAMPLIFIER / LIMITER  AND DETECTOR 5,5MHZ

TIP33A:Designed for general−purpose power amplifier and switching
applications.

Bipolar Transistors - BJT
Transistor Polarity:     NPN    
Collector- Emitter Voltage VCEO Max:     60 V    
Collector- Base Voltage VCBO:     60 V    
Emitter- Base Voltage VEBO:     5 V    
Collector-Emitter Saturation Voltage:     1 V    
Maximum DC Collector Current:     10 A    
Pd - Power Dissipation:     80 W    
Gain Bandwidth Product fT:     3 MHz    
Minimum Operating Temperature:     - 65 C    
Maximum Operating Temperature:     + 150 C

BU128 : 

Material of Transistor: Si
Polarity: NPN
Maximum Collector Power Dissipation (Pc): 62 W
Maximum Collector-Base Voltage Vcb: 300 V
Maximum Collector-Emitter Voltage Vce: 200 V
Maximum Emitter-Base Voltage Veb: 5 V
Maximum Collector Current Ic max: 10 A
Max. Operating Junction Temperature (Tj): 150 °C
Transition Frequency (ft): 80 MHz
Forward Current Transfer Ratio (hFE), MIN: 40
-
Package: TO3

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.

- 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.

 

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 exhibit 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, R14 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 or both and ics.

TBA 311 TV SIGNAL PROCESSING CIRCUIT


The TBA311 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.