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

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Old 24th Oct 2020, 10:19 am   #61
peter_scott
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Default Re: Restoration of a 1937 first generation pre-war television (HMV 900)

Really good restoration. I love it!

Peter
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Old 24th Oct 2020, 3:13 pm   #62
beery
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Default Re: Restoration of a 1937 first generation pre-war television (HMV 900)

Hi Catkins,
I really love your approach to vintage TV restoration. It is very similar to my approach. If rust etc is not too bad, then l tend to leave as is, of course it is quite bad then more drastic action is required.
I like my sets to look there age if possible.
I also agree about the keeping the 1946 repairs. With my HMV905 I had to choose a point in time to take it back to. Given that in the late 50s
/early 60s it had received radio repairs when the TV parts were ripped out, I decided to remove all parts from that time to put it back to how it would have looked in the early 50s, which was when the last repairs were carried out in the vision detector section (one of the few bits of TV circuity left). If say I had decided to replace the paxolin board containing ht decoupling electrolytics (which were fitted by EMI in 1946) with a reproduction of the pre-war capacitor box, it would have meant removing the last vestages of the sets history (as a complete TV and Radio).

Notes on paper in oil caps with polarity markings. The minus sign often indicates the outer foil, which will be nearest to the case. The manufacturer would specify that the minus connection is closest electrically to the chassis 0v rail. Indeed in some capacitors, such as the dual section EHT reservoir and smoothing capacitor the outer foil is internally connected to the case.
When dealing with an electrostatic set with negative EHT, you will find that the negative EHT is connected to the positive terminal of the smoothing capacitor, which is confusing when you first see it.

Some wax capacitors have a vertical line at one side of the label to indicate the outer foil. This is occasionally important in RF circuits, where the outer foil should be connected to the earthy end of the circuit. The modern day Vishay tubular caps have such a marking, but the cheaper, but still good Chinese caps don't have this indicated. However it doesn't really matter in the big scheme of things.

For those that don't know, pre-war EMI waxies stand out from their post-war counterparts by the fact that they have no wax sealing at the ends, which kind of makes you wonder about their reliability back in the day.

Cheers
Andy
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Old 24th Oct 2020, 4:23 pm   #63
peter_scott
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Default Re: Restoration of a 1937 first generation pre-war television (HMV 900)

Quote:
Originally Posted by beery View Post
Notes on paper in oil caps with polarity markings. The minus sign often indicates the outer foil, which will be nearest to the case. The manufacturer would specify that the minus connection is closest electrically to the chassis 0v rail. Indeed in some capacitors, such as the dual section EHT reservoir and smoothing capacitor the outer foil is internally connected to the case.
Cheers
Andy
That's interesting info.

Thanks Andy.

Peter
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