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#1
11-14-2021, 05:43 PM
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1950 Admiral 21D1- interference in audio help!
I redid this set, new caps, resistors, all good tubes:
Has an excellent bright picture, but there is a lot of scratchy loud interface in the audio, and volume is very low, needs to be turned all the way up to hear it... Any ideas what could be causing it, been fooling with it for a year now and no luck... 
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#2
11-14-2021, 07:32 PM
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Quote:
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#3
11-14-2021, 08:20 PM
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Quote:
The fine tuning turned all the way to the left does make the volume louder and clearer, but still lots of scratchy interference noise...
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#4
11-15-2021, 05:53 PM
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You could pull the 6AU6 sound IF tube to check if the noise goes silent, if so you'll know if the noise source is not after that stage. If it's still noisy try pulling the 6av6 audio frequency amp tube. Basically you need to divide things up to narrow down where the noise is jumping in.
Last edited by Kevin Kuehn; 11-15-2021 at 06:00 PM.
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#5
11-15-2021, 08:38 PM
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Could be SMD (silver mica disease) in the sound IF cans. I know earlier Admirals suffered from it.
If you've eliminated every other suspect and the problem remains, try popping the shield off the sound IF transformer and ratio detector. There may be a mica cap like this that is exposed to the environment. You can carefully clip them out and tack in a new mica cap. 
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