Model 27-84 BUZZ?Humm? - Printable Version

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Model 27-84 BUZZ?Humm? - Bruce - 02-15-2025

Drowning in a overloud buzz/Humm. Have already changed filter caps,bakelite blocks( caps),out of speck resistors,checked many grounds. Changed & tested tubes,usual voltage checks, removing 6j7's an still have buzz/humm.Running short on ideas!
Thank everyone for any direction resolving
Bruce

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RE: Model 27-84 BUZZ?Humm? - radiorich - 02-15-2025

Hello Bruce,
First all do mean a 37-84b ?

Did you take any before and after pictures ?
is it a buzz like when you touch input to amp or is it a hum ?

Sincerely Richard

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RE: Model 27-84 BUZZ?Humm? - Arran - 02-15-2025

I would have to look at the schematic but it's not uncommon in 1930s AC radios to have the negative of one filter cap connected to the center tap of the high voltage winding, and the other to chassis, with a series of wire wound resistors in-between. It's a common mistake a lot of people make because they are used to working on 1940s and 50s radios that have the tubes cathode biased rather then fixed bias, so in effect one filter cap is open circuit if you connect both to the chassis.
Regards
Arran

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RE: Model 27-84 BUZZ?Humm? - morzh - 02-15-2025

Depends on the type of hum. SOme is made by outside devices.

Try installing an X-cap (0.2-0.5uF) across the AC line, while still keeping the Y-cap (yours is 0.015uF, I think) where it is; also try to see if inverting the plug position 180 degrees affects it.

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