Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: stagam on March 28, 2023, 01:21:38 pm

Title: Ampeg B15s oscillation problem
Post by: stagam on March 28, 2023, 01:21:38 pm

I have Ampeg B15s amp that I recapped and can get great signal up to output tubes 7027 but has oscillation at full volume with nothing on input. Anyone out there that can assist me with problem?

Title: Re: Ampeg B15s oscillation problem
Post by: tubeswell on March 31, 2023, 02:56:40 pm

NFB loop backwards?

Title: Re: Ampeg B15s oscillation problem
Post by: cfortner on August 25, 2023, 04:00:32 am

Quote from: tubeswell on March 31, 2023, 02:56:40 pm

NFB loop backwards?

Gridstopper at V1? Resistor to ground at grid of V1?

Title: Re: Ampeg B15s oscillation problem
Post by: pdf64 on August 25, 2023, 05:46:59 am

Quote from: stagam on March 28, 2023, 01:21:38 pm

I have Ampeg B15s amp that I recapped and can get great signal up to output tubes 7027 but has oscillation at full volume with nothing on input. Anyone out there that can assist me with problem?

Are the shorting contacts on the input socket functioning correctly, ie shorting the input stage grid to ground when nothing is plugged in?
Is this the correct schematic for the amp in question? https://el34world.com/charts/Schematics/files/Ampeg/Ampeg_b15s_revd.pdf