TELEFUNKEN PORTI 1200 T1242B YEAR 1972.

 The TELEFUNKEN PORTI 1200 T1242  is a 14 inches (31cm) portable B/W television with 6 programs preselection keyboard with potentiometers tuning search system. ALL commands are above located inclusive a headphone jack connector quite rare for a portable B/W.

 The TELEFUNKEN PORTI 1200 T1242B  was first TELEFUNKEN Portable tv set which was featuring powering both Mains and with incorporated rechargeable battery.

The rechargeable battery combination includes a housing having an open bottom cabinet portion fixed by a screw,  through which batteries to be charged are to be inserted, spring means within the housing for urging the batteries outwardly of the housing and a cover for the open portion of the housing.The batteries in the housing are retained therein by a portion of the latch whenever the cover is pivoted away from the open portion of the housing.  This system includes a charge current source constituted by a transformer arrangement within the housing.

A method for charging batteries using a solid state battery charger is disclosed which includes the steps of supplying a constant current to the batteries being charged until the battery voltage reaches a first threshold voltage value, supplying a constant voltage to the batteries being charged until current being drawn by the batteries reaches a threshold current value and supplying a constant current to the batteries being charged until a voltage rise per unit time threshold is met.

Back side a 3  positions switch  is determining if the Television has to be powered by mains / battery / battery charging.

It has a Transistorized horizontal deflection circuits  made up of a horizontal switching or output transistor, a diode, one or more capacitors and a deflection winding. The output transistor, operating as a switch, is driven by a horizontal rate square wave signal and conducts during a portion of the horizontal trace interval. A diode, connected in parallel with the transistor, conducts during the remainder of the trace interval. A retrace capacitor and the deflection yoke winding are coupled in parallel across the transistor-diode combination. Energy is transferred into and out of the deflection winding via the diode and output transistor during the trace interval and via the retrace capacitor during the retrace interval.

In some television receivers, the collector of the horizontal output transistor is coupled to the B+ power supply through the primary windings of the high voltage transformer.

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.

 
In the end of the 60's increasingly attention was focused on the varicap diode tuner as the latest, sophisticated means of television receiver frontend tuning in both colour and black and white sets.
The main purpose of this article is to investigate the servicing problems associated with this comparatively new method of tuning.

First however let's briefly recap on the principles involved in this tuning system:
The tuners use variable capacitance (or "varicap") diodes as the variable tuning elements: the effective capacitance of the diodes is controlled by the reverse bias applied across them, tuning being achieved by varying this voltage. As the reverse bias across a varicap diode is increased so its junction depletion region widens thus reducing its capacitance.
A VHF/ UHF television tuner is constructed in accordance with the present invention includes a preselector tuned circuit having a solid state voltage controlled capacitor as its tunable element, a radio frequency amplifier coupled to the preselector circuit and alsoother circuit to perfect the signal receiving capability and the application the like.


Considering the Mechanical Tuner Problems:
To get the servicing problems in perspective let us next consider the tuning arrangements previously used.
The earliest of these, employed on v.h.f., was the switched tuner which was either of the turret or incremental type. The turret tuner substituted a coil bearing "biscuit" mounted on the rotating drum or turret when channels were changed. Twelve positions were normally provided, with a fine tuning knob to adjust the local oscillator frequency. As its name suggests the incremental tuner simply added more inductance to the tuned circuits at every downward channel movement: thus the highest inductance was present on channel one and the least on channel 12 (which normally covered 13 as well with manipulation of the fine tuner).
The movement towards u.h.f. TV working, initially with dual standard sets and later with single standard ones, brought about the need for u.h.f. tuners. In the earliest u.h.f. receivers valve tuners which were not particularly efficient were used.

The drive mechanism was usually a dual speed rotary system calibrated from channels 21 to 68. Experience in the field indicated that 625 line television was in many cases considered by the viewer to be inferior to 405 -line reception, on account of the poor signal to noise ratio achieved by the valve tuners. Many viewers were not prepared to use external u.h.f. aerials of course, having achieved satisfactory reception on v.h.f. with an indoor aerial: this aggravated the situation even more.

Another aspect which caused difficulty was the care needed to tune in a u.h.f. channel using a rotary tuner covering the whole of Bands IV and V. Many viewers simply could not tune in BBC 2 or ZDF or ORF or any channel correctly with such a tuning mechanism, finding that they had passed right over the channel they wanted before realising what they had done.

The advent of transistor tuners rapidly improved the quality of u.h.f. reception but use of a rotary mechanism was continued by many manufacturers. Thus while potential reception was improved the same tuning difficulties remained and viewers continued to gravitate towards 405 line viewing using the "old faithful" switched tuner. The operational breakthrough came with the introduction of the push-button u.h.f. channel change.

The mechanism is basically simple. Adjustable push buttons press down on a lever bar which in turn rotates the tuner's variable capacitors to the appropriate position. Each button is capable of tuning over the entire u.h.f. bands and this leads to customer confusion at times when after some adjustments which were too heavy handed they find themselves receiving ITV on a BBC button or a ORF and ZDF broadcasting or any channel possible !

Mechanical Faults:
Mechanical tuning obviously has its snags. There are for example contact springs which earth the tuning capacitor and go intermittent. This gives rise to the most random tuning defects, capable of driving the. most patient viewer to a state of total exasperation. It is also possible for the rotation mechanism to hang up and jam intermittently, or just become sticky, so that the reset accuracy of the mechanism is impaired and the receiver has to be retuned every time the channel is changed.

The vanes in the tuning capacitor can also short out at different settings, thereby eliminating some channels. The Varicap Tuner It will be seen then that mechanical defects can cause very irritating fault symptoms. If one thinks along the lines that anything mechanical is nasty, then the elimination of mechanical parts can only be to the good.

The logic of this is splendid provided the electronic replacement for the mechanical system is more reliable! Otherwise we are leaping out of the frying pan into the fire! In the light of experience gained with mechanical tuning devices it seems great that with the varicap tuner we have at last dispensed with the dreaded rotary tuning capacitor, replacing it instead with a variable voltage to the tuner.

Let us think about this however since things are never quite as simple as they first appear. The tuning voltage has to be variable in order to tune the receiver. Obviously then a means of varying the voltage has to be provided to act as the tuning control.
As it is a voltage that has to be varied the tuning control takes the form of a potentiometer., Now we have returned to a mechanical system again, though in a less complex form.A potentiometer is required for each channel, selected by pressing the appropriate channel button.
We have lost a tuning capacitor and its rotating mechanism and gained a set of pots and selector switches therefore. Provided the pots and switches are mechanically more reliable than the tuning capacitor we should be better off-or should we?


Need for Voltage Stabilisation.
The voltage selected by the pots cannot be allowed to drift otherwise the receiver will go off -tune. The voltage supply to the potentiometers has to be stabilised therefore and a stabilising zener diode or integrated circuit (TAA550) .is needed for this purpose.


Any failure in this part of the circuit will give rise to tuning drift or worse, a total loss of reception. A short-circuit TAA550 for example will completely remove the tuning voltage while if it is open circuit the tuning can vary with picture brightness. Likewise any intermittency in the potentiometers or associated switching and/or resistors can also cause problems.


Relative Reliability of Tuners:
It will be seen then that in order to lose our troublesome mechanical arrangement we have had to introduce considerably more electronics which we trust are going to be more reliable. In addition we have not so far considered the relative reliability of the varicap tuner itself compared with the mechanical type. Since two r.f. transistors are generally used to compensate for the reduced Q of the varicap tuned circuits we immediately have twice the likelihood of an r.f. stage breaking down!

And being semiconductors the varicap diodes themselves are more likely to fail than the sections of a ganged tuning capacitor. It is reasonable then to conclude that if mechanical faults are the most prevalent the use of varicap tuners will make life easier. Mechanical faults are generally not too difficult to sort out however and the field engineer can often cope with them in the home. Can the same be said of the varicap tuner? It seems that this type of tuner does not need so much attention as its mechanical counterpart but is likely to throw up some much more difficult faults when it does, resulting in bench repairs being needed. So far my own experience has indicated that varicap tuning faults nearly always need servicing on the bench.

Generally speaking it seems true to say that varicap tuners themselves are adequately reliable: the snags result from the tuning system and stabilised power supply.


Tuning Drift with Varicap Tuners:
If a varicap tuned receiver is constantly drifting off tune the +30V supply should be the number one suspect. It is best to connect an Avometer permanently to the supply so that it can be precisely monitored-if necessary write down the exact voltage measured. If the receiver drifts, check the voltage. If it has changed, even slightly, this may well be enough to be the cause of the fault. To pinpoint and confirm the diagnosis aerosol freezer should be applied to the stabiliser i.c. or zener. If the voltage returns to normal or changes wildly for the worse the stabiliser is almost certainly the cause of the trouble and should be replaced.

A prolonged soak test should then be carried out. Another point concerning varicap tuners arises with their use in colour receivers.

 There were  makers of the most expensive colour receiver on the market still didn't use a varicap tuner but instead use a mechanical one. The makers' claim is that the signal to-noise ratio of the varicap tuner is inadequate for their colour standards. Undoubtedly the results obtained on the receiver seem to confirm this. Interestingly, the same manufacturers use varicap tuners in their black -and -white receivers, and the tuning button system is often full of troublesome intermittent contacts. The varicap tuner has its advantages and disadvantages then. Probably the simplest comment would be to say that when it is good it is very very good but when it is bad it is horrid!

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

Springs component in old tv's tuner :
Most old televisions tuning mechanisms were incorporating coil springs in one form or another for various functions. They can be of the compression type which are wound with spaces between adjacent turns and are intended to be squeezed under pressure : when released they expand to their original form. The mounting springs under record-player turntable units are examples of this type. Alternatively the spring can be of the expanding variety. The coils are wound closely together with adjacent turns touching. The applied tension tends to pull them apart and they exert a contracting force to counteract this and pull the linked components together. In the majority of applications this type is used. Springs often become damaged by being over stretched, or the end loop breaks. More frequently the spring simply becomes detached and disappears. Thus the engineer is faced with the task of finding and fitting a replacement. While it is possible to apply to the makers of the equipment for the right spring this involves delay and of course there is always the problem of identifying the right one out of the many used in the particular mechanism. For this reason many engineers find it more convenient to make their own replacements.

Making a Coil Spring: The operation was quite simple, the equipment needed being a wheelbrace, vice, selection of long screwdrivers with varying diameter shanks and a supply of piano wire of various gauges. The wheelbrace is mounted horizontally in the vice with the wheel uppermost and a screwdriver chosen and inserted into the chuck with the blade foremost. This serves as a mandrel on which the spring can be wound. Because a spring expands slightly in diameter after it is wound the diameter of the screwdriver shank should be a little less than the required inside diameter of the spring. One end of the piano wire should be inserted in the chuck and secured to prevent it coming free. The wheel is then slowly turned and the wire taken up around the screwdriver shank. Keep the wire taut and pull it backward (see Fig. 1) toward the chuck at an angle which keeps the adjacent turns together but does not make a turn ride over the top of its predecessor. When the spring has reached the required length cut the wire and remove the springand screwdriver from the chuck.
As an aid in determining the size of the spring required-especially if the original is lost and there is no pattern to make a comparison with-here are a few observations on the characteristics of coil springs as determined by their dimensions.
Properties of Coil Springs: There are two main properties of a spring, the length to which it can be expanded in comparison to its closed length and its tension or strength in the expanded state. If a coil spring is expanded too far its coils will not return to their original position and the spring is said to be stretched. The amount that a spring can be expanded without becoming stretched is governed by the number of turns and the diameter. The greater the number of turns the less each one has to deviate from its resting position for the complete spring to reach a particular length. Also the greater the diameter the smaller the strain and therefore the more the spring can be expanded. The strength of a spring is related to the gauge of wire and the diameter. A heavy gauge will obviously give greater tension than a lighter one but also a spring with a large diameter will exert less force than a smaller one because as we have seen there is less strain when it is expanded. More force is exerted when the spring is well expanded than when it is nearly closed. If therefore we need a spring that is strong and will stretch a long way we need a large number of turns but not so many that the spring is too long in its closed position. It needs to be of fairly large diameter but as this will make it weaker we must compensate by using a heavy gauge of wire. A weak spring with a long stretch is easily made with thinner wire and a large diameter while a strong spring with a short stretch need have few turns and small diameter. So the various factors are interdependent and although spring design can be quite an exact art-by varying the various parameters-something suitable for the job can usually be made up by judicously estimating the size from the foregoing principles. If a spring has become stretched nothing can be done to restore it by squeezing it up as it has now become a compression spring and the expanded state is its normal one. Rather than winding a completely new spring however the old one can be unwound on a wheelbrace-by reversing the winding process and then rewound tightly. Proper unwinding is essential, not just pulling the spring out straight, because this will produce kinks.
Leaf Springs: From coil springs we turn to leaf springs. These were used as contacts in tuner units and are also were used in the press  button channel selector of the Philips colour TV range and other fabricants. To make a positive contact the leaf spring must be tensioned just right. In the case of the turret tuner the leaf must be so sprung that the contacting stud moves it about a tenth of an inch away from the resting position. If as sometimes happens contact is made without much movement of the leaf there will be little if any pressure and the contact will very likely be intermittent. If on the other hand the leaf is adjusted too far forward it may be caught by the edge of the coil biscuit and crumpled when the turret is rotated.

Telefunken (WAS) is a German radio and television apparatus company, founded in 1903, in Berlin, as a joint venture of two large companies, Siemens & Halske (S & H) and the Allgemeine Elektricitäts-Gesellschaft (General Electricity Company).

The name "Telefunken" appears in:

* the product brand name "Telefunken";
* AEG subsidiary as Telefunken GmbH in 1955;
* AEG subsidiary as Telefunken AG in 1963;
* company merged as AEG-Telefunken (1967–1985);
* the company "Telefunken USA" (2001). Now Telefunken Elektroakustik (2009)
* the company "Telefunken semiconductor GmbH & Co KG" Heilbronn Germany (2009).
* the company "Telefunken Lighting technologies S,L" (2009)

The company Telefunken USA[1] was incorporated in early 2001 to provide restoration services and build reproductions of vintage Telefunken microphones.

Around the turn of the 20th century, two groups of German researchers worked on the development of techniques for wireless communication. The one group at AEG, led by Adolf Slaby and Georg Graf von Arco, developed systems for the German navy; the other one, under Karl Ferdinand Braun, at Siemens, for the German army.

When a dispute concerning patents arose between the two companies, Kaiser Wilhelm II decided that the two companies were to be joined, creating on 27 May 1903 the company Gesellschaft für drahtlose Telegraphie System Telefunken ("The Company for Wireless Telegraphy Ltd."), and the disputed patents and techniques were invested in it. This was then renamed on 17 April 1923 as Telefunken, The Company for Wireless Telegraphy. Telefunken was the company's telegraph address. The first technical director of Telefunken was George Graf von Arco.

Starting in 1923, Telefunken built broadcast transmitters and radio sets.

In 1928, Telefunken made history by designing the V-41 amplifier for the German Radio Network. This was the very first two stage, "Hi-Fi" amplifier which began a chapter in recording history. Over time, Telefunken perfected their designs and in 1950 the V-72 amplifier was born. The TAB (a manufacturing subcontractor to Telefunken) V-72 soon became popular with other radio stations and recording facilities and would eventually come to help define the sound of most European recordings. The V-72S was the only type of amplifier found in the legendary REDD-37 console used by the Beatles at Abbey Road Studios on every recording prior to Rubber Soul. Today the V-72 is still the most sought after example of Telefunken's design and over 50 years later continues to be the benchmark by which all other tube based microphone preamplifiers are measured. In 1932, record players were added to the product line.

In 1941 Siemens transferred its Telefunken shares to AEG as part of the agreements known as the "Telefunken settlement", and AEG thus became the sole owner and continued to lead Telefunken as a subsidiary (starting in 1955 as "Telefunken GmbH" and from 1963 as "Telefunken AG").

During the Second World War Telefunken was a supplier of vacuum tubes, transmitters and radio relay systems, and developed radar facilities and directional finders, aiding extensively to the German air defense against British-American Aerial Bombing. During the war, manufacturing plants were shifted to and developed in West Germany or relocated. Thus, Telefunken, under AEG, turned into the smaller subsidiary, with the three divisions realigning and data processing technology, elements as well as broadcast, television and phono. Telefunken had substantial successes in these markets during the time of self-sufficiency and also later in the AEG company. Telefunken was also the originator of the FM radio broadcast system. Telefunken, through the subsidiary company Teldec (a joint venture with Decca Records), was for many decades one of the largest German record companies, until Teldec was sold to WEA in 1988.

In 1959, Telefunken established a modern semiconductor works in Heilbronn, where in April 1960 production began. The works was expanded several times, and in 1970 a new 6-storey building was built at the northern edge of the area. At the beginning of the 1970s it housed approximately 2,500 employees.

In 1967, Telefunken was merged with AEG, which was then renamed to AEG-Telefunken. During this era, Walter Bruch developed the PAL color television for the company, in use by most countries outside the Americas today (i.e. United Kingdom - PAL-I), and by Brazil (PAL-M) and Argentina (PAL-N) in South America.

The mainframe computer TR 4 was developed at Telefunken in Backnang, and the TR 440 model was developed at Telefunken in Konstanz. They were in use at many German university computing centres from the 1970s to around 1985. The development and manufacture of large computers was separated in 1974 to the Konstanz Computer Company (CGK). The production of mini- and process computers was integrated into the automatic control engineering division of AEG. When AEG was bought by Daimler in 1985, "Telefunken" was dropped from the company name.

In 2005, Telefunken Sender Systeme Berlin changed its name to Transradio SenderSysteme Berlin AG. The name "Transradio" dates back to 1918, when Transradio was founded as a subsidiary of Telefunken. A year later, in 1919, Transradio made history by introducing duplex transmission. Transradio has specialized in research, development and design of modern AM, VHF/FM and DRM broadcasting systems.

In August 2006, it acquired the Turkish company Profilo Telra, one of the largest European manufacturers of TV-devices, with Telefunken GmbH granting a license for the Telefunken trademark rights and producing televisions under that name. In 2000, Toni Roger Fishman acquired The Diamond Shaped Logo & The Telefunken Brand Name for use in North America. The company "Telefunken USA" [2] was incorporated in early 2001 to provide restoration services and build reproductions of vintage Telefunken microphones. In 2003, Telefunken USA won a TEC Award for Studio Microphone Technology for their exact reproduction of the original Ela M 250 / 251 Microphone system. Telefunken USA has since received several TEC Awards nominations for the following microphone systems: the Telefunken USA M12 or C12 (originally developed by AKG), the R-F-T M16 MkII, and the AK47. The Historic Telefunken Ela M251 microphone system entered the MIX foundation's Hall of fame in 2006. In 2008, Telefunken USA won a second TEC Award for its new Ela M 260 microphone.

As a result of a conference held in Frankfurt in May 2009, Telefunken USA has been renamed Telefunken Elektroakustik ("Electrical Acoustics") Division of Telefunken and awarded the exclusive rights to manufacture a wide variety of professional audio products and vacuum tubes bearing the Telefunken Trade Mark, in over 27 countries worldwide. Telefunken Elektroakustik now uses the Telefunken trademark for Professional Audio Equipment & Component Based Electronics, such as Capacitors, Transformers, Vacuum Tubes in North America, South America, Europe, Asia and Australia.

TELEFUNKEN HISTORY:

" It is ironic that in the years since the introduction of PAL, Telefunken – the company that invented PAL – disappeared from the market after they were bought in the 1980s by the French company Thomson – a former SECAM protagonist.

There is further irony in the fact that even as the majority of European and Asian TV viewers benefit on a daily basis from their PAL standard TV pictures, the worldwide transition from analog to digital TV spells the end of this color standard as well as many other TV transmission standards.

What we have known as PAL, SECAM, or NTSC is now increasingly known as simply digital RGB or Y, Cr, and Cb color component signals encoded in a DVB (Digital Video Broadcasting) signal or one of its many variants such as DVB-T, DVT-S, DVB-C, DVB-H, or similar ones like your ATSC.

In the future, all this may in turn disappear into an abstract IP (Internet Protocol) packet, which would make traditional distribution channels obsolete. For example, major areas in Germany, and all of Austria may terminate their analog transmissions, replacing them with DVB-T or DVB-S only.

We will find out whether the 55th anniversary of PAL in 2018 will generate much of a resonance, if all analog TV transmissions – whether terrestrial, satellite, or cable – have been brought to an end. "

1903 – 1922
TWO ARCH RIVALS. ONE INNOVATIVE COMPANY

At the beginning of the last century, two rival research groups were working in the field of
wireless telegraphy. The Slaby-Arco group was represented by the radio-telegraphy department
of AEG, founded in 1899. The other as the Braun-Siemens group, represented by a company
called Gesellschaft für drahtlose Telegraphie, System Prof. Braun und Siemens & Halske
GmbH. Under the advice of Emporer Wilhelm II, the two groups merged to form the
Gesellschaft für drahtlose Telegraphie mbH company on May 27, 1903. And the rest is history.




A TELEFUNKEN FIRST
The very first Telefunken customers were the German Army and the Imperial Navy.
Telefunken was proud to deliver the first two transmitters for the new coastal radio station, Norddeich
Radio, in November 1905. In October 1906, the expansion of a much larger Nauen station was
completed with a range of 300 km and HF output of 10 kW. Welcome to the power of
Telefunken.


MEET DR. TELEFUNKEN

Dr. Georg Graf Von Arco was the first Technical Director and Managing Director of the
Gesellschaft für drahtlose Telegraphie mbH in 1903. He was also the holder of more than one
hundred patents. Among other inventions, he initiated the high-frequency mechanical
transmitter and the wavemeter. Necessity is the mother of invention. Or in this case, German
inventions.


1923 – 1936
TELEFUNKEN GOES COMMERCIAL

On April 17, 1904, the company changed its name to "Telefunken, Gesellschaft für drahtlose
Telegraphie", and on July 26, 1932 Telefunkenplatte GmbH officially began its commercial
activity with registered capital of 100,000 Reichsmarks.
The station in the Telefunken building, Tempelhofer Ufer 9 in Berlin, began broadcasting
concerts regularly two and a half months before the official start of the "Deutsche
Rundfunkverkehr". The world tour of the Graf Zeppelin airship in 1929 got off the ground by
using Telefunken transmitters, receivers and directional equipment exclusively.
Also, on October 31, 1928, during the 5th Grand German Radio Exhibition in Berlin, Telefunken
presented a television set with the Karolus-Telefunken system, a scanning process of film
images through a Mechau projector with a Nipkow disk, in public for the first time.


MEET TELEFUNKEN’S MAD SCIENTISTS

Dr. Hans Bredow is considered to be the "Father of Broadcasting". He was employed at
Telefunken from 1904 to 1919 as a Project Manager, and later as Managing Director.
Prof. Dr. Walter Bruch developed the very first electronic television camera, with which he
participated in the live broadcast of the Olympic Summer Games in Berlin in 1936. He also
earned international fame by inventing the PAL color television system. He joined Telefunken's
Television and Physical Research Department in 1935.
These two innovators thought out of the “TV box” and helped shape and make Telefunken what
it is today.


WELCOME TO RADIO TELEFUNKEN

The German radio station in Zeesen near Königswusterhausen (8 kW shortwave transmitter) was built by Telefunken and was officially placed in service on August 28, 1929. The Mühlacker radio station (60 kW output) was handed over on December 20, 1930. Telefunken is now in, and on, the air.


TELEFUNKEN GOES FOR THE GOLD, SILVER AND BRONZE

In 1935, Telefunken equipped the Olympic Stadium, the Maifeld and the Dietrich-Eckhardt
Stage with electrical-acoustic equipment for the Olympics. On August 1, 1936 at the XI Olympic
Summer Games in Berlin, an electronic television camera, known as the Ikonoskop, was used
for the first time for a direct transmission. Again, another Telefunken first. And second. And third
1936- 1954


NOW PLAYING ON CHANNEL TELEFUNKEN

The first fully electronic television studio equipped by Telefunken for the Deutsche Reichspost
was opened with a live broadcast in August 1938. The 500 kW long wave transmitter in
Herzberg, also known as the most powerful German broadcast transmitter, was supplied by
Telefunken and began to operate on May 19, 1939.


IT’S NOT A MERGER. IT’S A POWERHOUSE

On September 24, 1941, AEG took over the 50% of Telefunken shares owned by Siemens &
Halske AG valued at 20 million Reichsmarks. Thus, Telefunken became a 100% subsidiary of
AEG. In exchange, Siemens & Halske AG received the shares of Eisenbahn-Signalwerken,
Klangfilmgesellschaft mbH and Deutsche Betriebsgesellschaft für drahtlose Telegraphie
(DEBEG) owned by AEG. Strength in numbers, indeed.


POST WWII

The reconstruction after the World War II posed a particularly difficult challenge to Telefunken.
All production facilities and equipment were destroyed, disassembled or confiscated and many
valuable experts were scattered around the world. Rebuilding began in West Germany and
Berlin in 1945, and the production of tubes and transmitters was resumed the same year. But
growth was on the way.



THE TELEFUNKEN COME BACK

In 1953 Telefunken already comprised six plants and five sales offices in Berlin, Ulm,
Frankfurt/Main and Hanover again.The range of products consisted of long-range
communications systems, radio and television transmitters, marine radios, commercial
receivers, directional and navigation systems, radar devices, deci and UHF directional radio
connections, mobile radio systems, portable radio systems, HF heat generators, measuring
equipment, electro-acoustical systems, music centers, record players, transmitter tubes, radio
tubes, special tubes and quartz crystals. As you can see, Telefunken was relentless and has
come a long way.


PROF. DR. DR. WILHELM T. RUNGE THE FIRST

Prof. Dr. Dr. Wilhelm T. Runge (1895-1987) performed trailblazing work in radio and radar
technology and played a significant role in the development of microwave in Germany. He was
especially renowned internationally in the field of high-frequency technology. As well as for
having a few, very important titles before his name.


1955 – 1962
AS TELEFUNKEN GROWS, SO DOES ITS NET WORTH

The name of the company was changed to Telefunken GmbH on January 4, 1955. Due to the
expanded business activities of Telefunken, AEG increased the capital of the company to DM
100 million in 1958.


THE FIRST GERMAN STEREO STUDIO. BROUGHT TO YOU BY TELEFUNKEN

The Sender Freies Berlin (SFB) station ordered the first German stereo studio in 1961. The
harbor radar system, supplied by Telefunken, was officially placed for service in Hamburg
Harbor in August 1962, while the first German transistor receiver (six transistors) was produced
in a test series in 1956. Prof. Dr. Walter Bruch filed the fundamental PAL "time decoder" patent
on December 31, 1962. It was the first German stereo studio of its kind, and Telefunken sought
to it that there was nothing else quite like it.


1963-1978
WHAT’S IN A NAME?

Telefunken GmbH became Telefunken AG on July 5, 1963. On June 23, 1966, the General
Shareholder Meeting of AEG passed a resolution to integrate Telefunken AG into Allgemeine
Elektrizitäts-Gesellschaft. Based on an operating lease agreement, the business activities of
Telefunken were transferred to AEG effective January 1, 1967, and were continued under the
combined name AEG-Telefunken. In March 1968, AEG-Telefunken developed a new mediumrange
radar system (Type SER-LL), which was able to detect targets at an altitude of 24,000
meters at a distance of 280 kilometers. Telefunken expands on land, as well as in the air.


TAPE RECORDERS WORTH MILLIONS

AEG-Telefunken delivered the two-millionth tape recorder, a Magnetophon 204 TS, on August
5, 1969. The ten-millionth black-and-white television picture tube was produced in Ulm on
January 27, 1970. The numbers are astounding. As is Telefunken.AEG-Telefunken delivered the
two-millionth tape recorder, a Magnetophon 204 TS, on August 5, 1969. The ten-millionth
black-and-white television picture tube was produced in Ulm on January 27, 1970. The
numbers are astounding. As is Telefunken.


ECONOMIC SLOWDOWN

There was a worldwide economic slowdown in the wake of the oil crisis in 1974. The
competition in consumer electronics sector also became more difficult due to Japanese
suppliers. The only profitable divisions of the company at this time were telecommunications
and traffic technology. But Telefunken, as usual, was known for their resilience.


1979- 1983
THE NAME GAME CONTINUES

The name of the overall company was changed to AEG-Telefunken Aktiengesellschaft on June
21, 1979. The "Aktiengesellschaft" [stock corporation] suffix was necessary due to a new law in

the European Community. In 1979, AEG-Telefunken supplied the complete telecommunications
and high-voltage equipment for the International Congress Center (ICC) Berlin, valued at DM 50
million. In January 1983 the company received an order for simulation systems for electronic
battle simulation for training Tornado crews of the German Luftwaffe and Navy. The total value
was at DM 37 million. The net worth: priceless.


TOUGH TIMES FOR TELEFUNKEN

Court composition proceedings were opened against the assets of AEG-Telefunken AG by the
District Court in Frankfurt / Main on October 31, 1982.
The District Court Frankfurt / Main confirmed the composition of AEG-Telefunken AG in
accordance with the petition filed and closed the proceedings on September 19, 1984.
Even during this difficult financial situation, AEG-Telefunken continued its business and founded
AEG-Telefunken Nachrichtentechnik GmbH (ATN), in Backnang, Germany, together with
Bosch, Mannesmann and Allianz Versicherungs-AG in 1981, as well as Telefunken electronic
GmbH (TEG) in the field of electronic components (semiconductors) together with United
Technologies Corporation (UTC), USA in 1982.
On July 1, 1992, AEG-Telefunken and Deutsche Aerospace (Dasa) founded Telefunken
Microelektronic GmbH (TEMIC), into which Telefunken Elektronic GmbH was integrated among
others. But Telefunken was determined to prevail.


A FINAL, BUT NOT LAST, TURN

Effective March 31, 1983, the French group Thomson-Brandt S.A. took over 75 percent of the
AEG-Telefunken shares in Telefunken Fernseh und Rundfunk GmbH, Hanover, Germany,
including its German and foreign subsidiaries. The remaining 25 percent were supposed to
follow on January 31, 1984. Daimler-Benz AG entered the company in autumn of 1985 and
decided in Autumn 1995 to dissolve the legal entity and transferred the remaining assets to
EHG Electroholding GmbH. Thus, the history of the company was over. But not that of its
brands.
A historical overview is offered by the company archive of AEG-Telefunken in the "Deutsches
Technikmusem Berlin", Trebbiner Str. 9, 10963 Berlin.


1984 – 2004
INNOVATION YESTERDAY. TODAY. AND TOMORROW

Currently, the Telefunken brand and name rights lie with Telefunken Licenses GmbH,
Frankfurt/Main, Germany. This company is one hundred percent subsidiary of EHG
Elektroholding GmbH, Frankfurt/Main.
EHG, on the other hand, is the legal successor of AEG Aktiengesellschaft. The licensor is
Licentia Patent-Verwaltungs GmbH, Frankfurt/Main, Germany. A differentiation is made
between brand licensing agreements, name use agreements and combined agreements. And
third-party use always requires the written approval of the licensor.
In 2003, Telefunken can look back at one-hundred years of brand history. In the past,
Telefunken was associated with significant technical developments and enjoyed the reputation
of a successful German company.
The Telefunken brand is registered in the official trademark registries of 118 countries. It
continues to be used under a variety of licensing agreements.
These are the topics that can be found in the commemorative volume "Telefunken After 100
Years - The Legacy of a Global German Brand."
Whether discovered on this website or in book, these topics should not only focus attention on
the past, but also simultaneously highlight the beginning of a strong Telefunken brand. Simply
put, it’s not just about where we’ve been. But also where we’re going.


2004 – 2009
TELEFUNKEN TODAY

Since December 2007, the trademark-right TELEFUNKEN rests with TELEFUNKEN Holding
AG, Frankfurt. Currently, TELEFUNKEN is the owner of more than 20,000 patents and active in over 130 countries around the globe.
Today, TELEFUNKEN stands for innovation and progress in the ever-changing world of
information and communications technology and is strictly focused on consumer quality – from
design concept to execution. And because of its strong heritage and long-standing tradition,
Telefunken has a high brand-awareness and a clear positioning in the field of premium
products.

Some References:

• M. Friedewald: Telefunken und der deutsche Schiffsfunk 1903–1914. In: Zeitschrift für Unternehmensgeschichte 46. Nr. 1, 2001, S. 27–57
• M. Fuchs: Georg von Arco (1869–1940) – Ingenieur, Pazifist, Technischer Direktor von Telefunken. Eine Erfinderbiographie. Verlag für Geschichte der Naturwissenschaften und der Technik, Berlin & München: Diepholz 2003
• L. U. Scholl: Marconi versus Telefunken: Drahtlose Telegraphie und ihre Bedeutung für die Schiffahrt. In: G. Bayerl, W. Weber (ed.): Sozialgeschichte der Technik. Ulrich Troitzsche zum 60. Geburtstag. Waxmann, Münster 1997 (Cottbuser Studien zur Geschichte von Technik, Arbeit und Umwelt, 7)
• Telefunken Sendertechnik GmbH: 90 Jahre Telefunken. Berlin 1993
• Erdmann Thiele (ed.): Telefunken nach 100 Jahren – Das Erbe einer deutschen Weltmarke. Nicolaische Verlagsbuchhandlung, Berlin 2003, ISBN 3-87584-961-2
•  

Einzelnachweise:

Schreibweise mit c siehe: - AEG-Teilschuldverschreibung von 1962

Marke „Telefunken“ in der Registerauskunft des Deutschen Patent- und Markenamtes (DPMA)

E. Thiele (Hrsg.): Telefunken nach 100 Jahren: Das Erbe einer deutschen Weltmarke. Nicolai, Berlin 2003, S. 19

Kurt Kracheel: Flugführungssysteme (Die Deutsche Luftfahrt, Band 20). Bernard&Graefe Verlag, Bonn 1993, ISBN 3-7637-6105-5, S. 119.

Operette 50W UKW. In: radiomuseum.org. Abgerufen am 28. Januar 2016.

Autosuper IA 50. In: radiomuseum.org. Abgerufen am 28. Januar 2016.

Farbfernseh-Tischempfänger PALcolor 708T. In: radiomuseum.org. Abgerufen am 28. Januar 2016.

Mini Partner 101. In: radiomuseum.org. Abgerufen am 28. Januar 2016.

Olympia-Partner. In: radiomuseum.org. Abgerufen am 28. Januar 2016.

Magnetophon 3000 hifi. In: radiomuseum.org. Abgerufen am 28. Januar 2016.

Fernseh-Tischempfänger FE8T. In: radiomuseum.org. Abgerufen am 28. Januar 2016.

Israelischer Konzern Elbit Systems eröffnet Büro in Berlin. In: bundeswehr-journal. 13. April 2018, abgerufen am 18. Januar 2019.

Telefunken Semiconductors Heilbronn: Die Lichter sind für immer aus, swr.de, 27. Februar 2015

LDL Berlin: Geschäftshaus Mehringdamm 32 & 34

LDL Berlin: AEG-Glühlampenfabrik

LDL Berlin: AEG-Telefunken-Gerätewerk

Telefunkenwerk Celle. vergessene-orte.blogspot.com

Ludwig Leisentritt: Die historische Entwicklung von Zeil am Main, hbrech.tripod.com
 

TELEFUNKEN PORTI 1200 T1242B CHASSIS T220 INTERNAL VIEW.

The TELEFUNKEN PORTI 1200 T1242B  CHASSIS T220 is a modular chassis which by construcition remembers the PALColor series
Chassis 711  712   712A    714     714A

- SN76001N0

- SN76660N0 TV Video IF Amplifier with AGC and Keyer Circuit

the remaining parts are realized with discrete components  many germanium and silicon.

AY102.

AU113.

AY105K

The tuning circuits has a large knob potentiometers tuning system which use voltage controlled capacitances such as varactor diodes as the frequency determining elements.
How AFC Circuit Works in B/W Analog Television Receiver:

Push-Button tuning on u.h.f. while being very convenient often leaves a margin of mistuning, especially after some wear and tear has occurred on the mechanism. Even dial tuning can lead to errors due to the difficulty many people experience in judging the correct point. Oscillator drift due to temperature changes can also cause mistuning. Automatic frequency control (a.f.c.) will correct all these faults. The vision carrier when the set is correctly tuned on u.h.f. is at 39.5MHz as it passes down the i.f. strip. Thus if at the end of the i.f. strip a discriminator tuned circuit is incorporated centred on 39.5MHz the discriminator output will be zero at 39.5MHz and will move positively' one side of 39.5MHz and negatively the other as the tuning drifts. This response is shown in Fig. 1.

If the tuning is not correct then the discriminator output is not zero and if this output is applied to change the reverse bias on a tuning diode mounted in the oscillator section of the u.h.f. tuner it will correct most of the error. Tuning, varicap or varactor diodes-to give them a few of their names-are junction diodes normally operated with reverse bias but not sufficient to bias them into the breakdown region in which zener diodes operate. The greater the reverse bias the lower their capacitance: a typical curve, for the PHILIPS BB105 or STC BA141 tuning diode, is shown in Fig. 2. All diodes 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.

Therefore a stable AFC circuit is developed:

A superheterodyne receiver having an automatic intermediate frequency control circuit with means to prevent the faulty regulation thereof. The receiver has means for receiving a radio frequency signal and mixing the same with the output of a superheterodyne oscillator. This produces an intermediate frequency signal which is coupled to a frequency or phase discriminator to produce an error signal for controlling the frequency of the superheterodyne oscillator. A regulation circuit is provided having an electronic switch to interrupt the feedback circuit when only unwanted frequencies tend to produce faulty regulation of the superheterodyne oscillator.


Power supply is realized with mains transformer and Linear transistorized power supply stabilizer, A DC power supply apparatus includes a rectifier circuit which rectifies an input commercial AC voltage. The rectifier output voltage is smoothed in a smoothing capacitor. Voltage stabilization is provided in the stabilizing circuits by the use of Zener diode circuits to provide biasing to control the collector-emitter paths of respective transistors.A linear regulator circuit according to an embodiment of the present invention has an input node receiving an unregulated voltage and an output node providing a regulated voltage. The linear regulator circuit includes a voltage regulator, a bias circuit, and a current control device.

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.



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.A selenium rectifier is a type of metal rectifier, invented in 1933. They were used to replace vacuum tube rectifiers in power supplies for electronic equipment, and in high current battery charger applications.

The photoelectric and rectifying properties of selenium were observed by C. E. Fitts around 1886 but practical rectifier devices were not manufactured routinely until the 1930s. Compared with the earlier copper oxide rectifier, the selenium cell could withstand higher voltage but at a lower current capacity per unit area.