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Old 16th Sep 2019, 2:30 pm   #54
Jac
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Join Date: Jun 2006
Location: Eindhoven, Netherlands.
Posts: 510
Default Re: Yet Another Bush TV22

Peter,

My TV22E (or F?) is a bit different from the TV22, being 625 lines, but I had a similar hum modulation problem.
Probing seems to point at the grid (pin 9) of V3 (ECL80), around where the unwanted hum appeared to get in.
Just hold a screwdriver to that pin and verify the hum gets worse - then you have the same problem.
As a (not-to-elegant) solution I disconnected R12-C12-R23-C19-R24 on top of the chassis, and replicated this circuit below deck.
This reduced the hum substantially.

Hope this helps a bit.

Jac
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