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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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18th Apr 2017, 6:59 pm | #41 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
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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. |
19th Apr 2017, 12:25 pm | #42 | |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
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Re: ETRONIC HV203 10" console. [1949]
Quote:
Grammont made TV sets that were very similar to the UK Pye sets made between 1946 to 1949. DFWB. |
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19th Apr 2017, 5:31 pm | #43 | |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
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Re: Etronic HV203 finally finished.
Quote:
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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19th Apr 2017, 6:32 pm | #44 | |
Heptode
Join Date: Mar 2017
Location: Cedar Grove, Wisconsin, USA.
Posts: 823
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Re: ETRONIC HV203 10" console. [1949]
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21st Apr 2017, 12:49 am | #45 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,444
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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. |
21st Apr 2017, 8:06 am | #46 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
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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. |