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Old 18th Apr 2017, 6:59 pm   #41
Heatercathodeshort
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Default Re: ETRONIC HV203 10" console. [1949]

The TRF receiver was very popular over here between 1946-50. Alexandra Palace channel 1 was the only TV transmitter serving London and the Home Counties. Sutton Coldfield on channel 4 serving the Midlands went on air in December 1949 requiring manufacturers to produce two versions of the same TRF receiver, one for channel 1 and one for channel 4.

With the opening of Holme Moss [Manchester channel 2] Kirk O Shotts [Scotland 3] and Wenvoe [wales 5] all the makers went over to tunable superhets.

The TRF receiver tended to produce better definition as the RF stages, some 4 or 5 vision RF amplifier valves could be stagger tuned over the required passband.

Early superhets tended to have a low IF frequency causing difficulty in obtaining the full bandwidth coupled with local oscillator drift problems. The early TRF receivers certainly gave a good account of themselves. U.S. receivers of course had to cater for a large number of channels almost from day one. John.
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Old 19th Apr 2017, 12:25 pm   #42
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Default Re: ETRONIC HV203 10" console. [1949]

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Originally Posted by usradcoll1 View Post
An interesting read, to be sure!

I was also amazed to find that some of the British sets used a TRF circuit, which was unknown here.
All of the sets built here were Superhet design. Even the inexpensive models and the foreign imports.
I believe there was a some TRF TV sets made in France for the 441 line standard.
Grammont made TV sets that were very similar to the UK Pye sets made between 1946 to 1949.

DFWB.
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Old 19th Apr 2017, 5:31 pm   #43
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Default Re: Etronic HV203 finally finished.

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Originally Posted by Argus25 View Post
Heatercathodeshort,

The set you have is certainly a wonderful example. The self oscillating line output stage for electromagnetic deflection was ,it appears, unique to 405 line television sets. It did not feature in American textbooks. The first time I encountered this design was in a "Philco" branded tv (not American Philco but English).

In any event, this particular Philco tv set, using an MW31-74 crt, had the lopty encased in a large aluminium cylinder, filled with oil, the EY51 mounted on the top. The line opt tube was a PL38, obviously suited to the application. The H linearity was excellent. Since a schematic was unobtainium at the time, I transcribed it from the set (a model BT1251L).. see attachment.

It would be interesting to document all the known tv models (and there won't be many) that used this unique self oscillating output stage.
Actually, I believe the Philco BT1251L is a rebranded Ferguson 968T.
Compare the circuits shown in the attachments. The PY31 damper diode is from the AC point of view effectively connected across the secondary of the line output transformer. Of course the function of the diode is not to damp the flyback pulse, it's the over swing that has to be damped.

DFWB
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Old 19th Apr 2017, 6:32 pm   #44
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Default Re: ETRONIC HV203 10" console. [1949]

Quote:
Originally Posted by Heatercathodeshort View Post
The TRF receiver was very popular over here between 1946-50. Alexandra Palace channel 1 was the only TV transmitter serving London and the Home Counties. Sutton Coldfield on channel 4 serving the Midlands went on air in December 1949 requiring manufacturers to produce two versions of the same TRF receiver, one for channel 1 and one for channel 4.

With the opening of Holme Moss [Manchester channel 2] Kirk O Shotts [Scotland 3] and Wenvoe [wales 5] all the makers went over to tunable superhets.
I thought, that was the reason for the TRF design. The set only had to receive one channel. In the US, there was many locations that only had one channel for a few years.
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Old 21st Apr 2017, 12:49 am   #45
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Default Re: ETRONIC HV203 10" console. [1949]

Circuit diagram of the Etronic ECV1523. The line output valve is now an EL38.
Note the capacitor C5 which is connected between the screen and suppressor grid of the EL38, this is the same circuit arrangement as found in the Plessey Mark one chassis. The circuit functions as a Miller transitron type of oscillator.

DFWB.
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Old 21st Apr 2017, 8:06 am   #46
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Default Re: ETRONIC HV203 10" console. [1949]

The feedback winding on the LOPT has gone David and it resembles the Plessey Mk1/2 circuit. They must have had the same problems that I have with the linearity 65 years ago! The EL38 a far more suitable valve and being a pentode lended itself with greater success than a tetrode.

The Mazda 6P28 and 20P1 were very stable when used in a self oscillating circuit but I think that Etronic did not want to divert from Cossor. I bet they pulled a Plessey chassis apart in an attempt to discover how it managed to work so well! J.
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