Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Lectroid on March 17, 2025, 09:26:46 am
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I now own a transistor amp and I need to go through it. I can debug a tube amp, but don't know much about solid state amps, except basic skills like how to test voltages and trace a signal, etc, like on tube amps.
[Edit:] I've learned the amp is not a Fender Frontman, but a Sidekick 65 Reverb. New schematic below. My apologies.
The previous owner said it had 'all kinds of problems,' but when I got it home and cleaned the pots (which were filthy), the amp sounds good to me. Clean channel, 'drive' circuit, reverb--everything works.
The only problem at all is a steady buzzing tone. It's volume decreased after I cleaned the pots, now it's about 20% of what it was, but it's still too loud. It sounds higher in pitch so I'm guessing a 120Hz hum. None of the pots (since cleaning) make any noise or affect the buzz.
All I know right now is that the PS is putting out a nominal 42VDC. I'll measure voltages today and see if the readings make sense. I'll try to find where the buzz enters the signal chain. If that gives me any insights, I'll report back.
Any suggestions how to proceed with a transistor amp? Things I should check? Things to look for?
Thanks for reading.
[moderator: please move as appropriate thanks]
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If it’s ‘a steady buzzing tone’, probably filter caps need replacing is my guess.
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@shooter,
My thinking too at first.
I'm going to kill this thread. I poked around in the amp today and found that moving three bundles of wire around killed the hum completely. So I just tied the bundles down mechanically and, sure enough, that stopped the hum. They connect the PCB connections to the collector, base and emitter of the power transistors. For a $150 amp, it's close enough. :icon_biggrin: