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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 13th Feb 2006, 10:51 pm   #1
FERNSEH
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Default Cossor 917 console TV set.

This set was very easy to get going. On initial inspection I noticed that the twin-triode frame and line oscillator valve was the wrong type, someone had fitted a Marconi B36 which is equivalent to the 12SN7GT. The correct valve is a 6SN7GT. All the other valves are the original Cossor branded types, some are made by Mullard such as the 6AM6/EF91 and 6AL5/EB91.

A number of capactors in the frame timebase needed replacement to get the linearity right and the coupling capacitor between the video amplifier and the sync separator was found to be leaky. That's all that needed to be done to get the results shown in the attachment.

The cabinet needs tidying up. I'll send before and after pictures soon.
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Old 14th Feb 2006, 6:39 pm   #2
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Default Re: Cossor 917 console TV set.

The picture shows the Cossor in it's present condition. It is rather bashed up and it will be tidied before it is sent to it's new owner in France.

A number of TV enthusiasts in France are becoming interested in 405 line TV.
I'm hoping to take delivery of some 1950s 819 line TV receivers.

DFWB.
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Old 24th Feb 2006, 11:12 pm   #3
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Default Re: Cossor 917 console TV set.

The cabinet of the Cossor 917 has been tidied up and looks a lot better now.
My only criticism about this set is that the sound output could be better.
Two 6AM6/EF91 pentodes are employed in the sound IF amplifier, a 6AL5/EB91 double-diode serves as the detector and noise limiter. There is no audio amplifier, AF from the double-diode goes straight to a 7C5 output beam tetrode.

DFWB.
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Old 25th Feb 2006, 9:16 am   #4
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Default Re: Cossor 917 console TV set.

Quote:
Originally Posted by FERNSEH
There is no audio amplifier, AF from the double-diode goes straight to a 7C5 output beam tetrode.

DFWB.
This is very common in british sets. Generateing much level at the detector
provides you a better linearity of demodulation and the dynamic range
is better too. The disadvantage is you don't have enough gain for a pic up
or so. In this case one RF valve , in some sets the oscillator, is used
as a sound amp.
So you may have an aglinement problem there.

Kind regards
Darius
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Old 25th Feb 2006, 7:03 pm   #5
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Default Re: Cossor 917 console TV set.

Hello Darius,
The sound output on many British sets of the early 50's particularly those using the MAZDA valve line up follows the practise you suggest but most sets of this type didn't give enough sound for living rooms above a moderate size. EKCO seemed to get it right and I never had complaints with these. The Murphy was very poor and many dealers fitted a 6AT6 [EBC90] in place of the 6AL5 [EB91] in order to provide more audio gain. [Rewired base of course] Later sets all used the triode pentode audio valve such as the PCL83/PCL82/PCL86 to provide sufficient spare audio under adverse conditions. Regards JOHN.
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Old 26th Feb 2006, 12:14 am   #6
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Default Re: Cossor 917 console TV set.

Some versions of the Cossor 916/7 series (the 918) were fitted with a three band broadcast receiver which employed three valves; a 7S7 triode-hexode, a 7B7 pentode IF amplifier and a 7C6 double-diode triode. The triode AF amplifier was active on TV and radio so the sound output would certainly be better than the TV only versions.
One model in the series, the TV only 12" 926, did employ a triode-pentode output valve, a 6AB8/ECL80.

DFWB.
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Old 2nd Mar 2006, 9:28 am   #7
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Default Re: Cossor 917 console TV set.

Good morning,
sorry but I don't beleve that a factory makes hundreds of sets that can
not turned loud. All my british sets don't have a sound preamp TV22 LV20
FV1 TS1105 and they work fine.
In my Rembrandt a EF80 was added, see picture attached. But after
repairing the discriminator it was not neccessary any more.

Kind regards
Darius
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Old 2nd Mar 2006, 9:44 pm   #8
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Default Re: Cossor 917 console TV set.

Hi Darius,
The 7C5 sound output valve employed in the Cossor 917 has a modest slope of 3,7mA/V @ 180V so perhaps that is why the set offers only sufficient audio output. The PL33 sound O P valve used in the TV22 is more sensitive at 9 mA/V.
The Pye FV1 has three stages of sound IF amplification and again uses the PL33.
Is your Rembrandt TV of GDR or Russian manufacture?

Regards,
David.
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Old 2nd Mar 2006, 10:28 pm   #9
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Default Re: Cossor 917 console TV set.

Hello again,
I think David has the answer with the sound output. The PL33 output valve is very high slope and the 6.3v version, the EL33 gave good volume without a preamp. The EBL31 [ A similar valve to the EL33 but with two diodes] was used in 'short superhets'. It is interesting to note that the Etronic ECV1523 that uses a 7C5 frame output valve also uses one as an oscillator to drive it!
The problem is Darius that British living rooms have always been on the small side. A number of sets with no audio pre amp may provide sufficient sound when new but slight alignment drift and component tolerances tended to make the situation worse. many of these sets were being used on the extreme limits of the fringe areas and under these conditions believe me there was only just about enough sound for comfortable listening. Feeding good quality signals into a receiver from home generated sources gives more reliable results compared to 'off air' reception. When I was a young lad I knew a senior engineer from a leading rental company that had continued problems with low audio. That is why all British makers had gone over to an audio preamp stage by around 1958. The large consoles such as the FERGUSON 990T [1951] had full push pull output using ECL80 triode pentodes and they really 'punched' it out but these were expensive luxury models designed for the larger living rooms. Regards John.
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Old 3rd Mar 2006, 6:24 pm   #10
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Default Re: Cossor 917 console TV set.

Quote:
Originally Posted by FERNSEH
Hi Darius,Is your Rembrandt TV of GDR or Russian manufacture?

Regards,
David.
Hi David, it is east german manufacture. Nice set with octal valves.
Get one they will be expensive soon.

Kind regards
Darius
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