Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dpm309 on October 13, 2025, 06:03:31 pm

Title: Fender Silver Face 100 Watt Twin Hum
Post by: dpm309 on October 13, 2025, 06:03:31 pm

Working on a 100 Watt Silver Face (MV model) that has an annoying hum. Replaced all of the tubes (they were all original) and am still getting the hum but when I turn the balance pot all the way to the right, it decreases somewhat. I don't think this amp has a bias pot. The volume pots do not change the level of hum even when turned down to 0. Will pull the chassis and to see if I see anything. A blackface conversion was done by the previous owner and the hum developed over time. I have attached what I think is the correct schematic.Any ideas/suggestions?Thanks,Danhttps://el34world.com/charts/Schematics/files/Fender/Fender_twin_reverb_sf_100_schem.pdf

Title: Re: Fender Silver Face 100 Watt Twin Hum
Post by: DeepBias on October 13, 2025, 06:59:58 pm

Leaky or failing filter capacitors ?

Title: Re: Fender Silver Face 100 Watt Twin Hum
Post by: tubeswell on October 13, 2025, 07:17:07 pm

Quote from: DeepBias on October 13, 2025, 06:59:58 pm

Leaky or failing filter capacitors ?

^This is what I’d look at first^ … Including the bias supply cap (if it’s the original white Mallory cap, it will be way past needing replacing by now)