Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: pompeiisneaks on February 19, 2017, 01:33:45 pm
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I don't have a schematic, and since it's newish, I doubt it's going to be anywhere, so that's making it a bit tricky to sort out. There's a really annoying high pitched buzz coming into the first input stage and it's only somewhat bad at the main input, but when you use the relay switched 'boost' it takes the second half of the triode and switches the cathode resistor to a different point it seems, and bypasses the cap. (or so I think per what I'm looking at) but honestly I think the buzz is just being amplified at that point. I tried swapping tubes and that didn't change the sound at all, and if I tap around with my chopstick, I only hear a bit of noise on the input pins themselves, I reflowed the solder on those and that bit of noise seems much quieter, but the actual buzz didn't change. Any ideas of what to look at? It seems like a 120Hz buzz, but I've checked all filter caps and they're good with respect to ESR and don't seem problematic (they're all, also only maybe 2 yrs old).
Ideas? Could this be the shielded cable from the input jacks? A bad input jack? A bad tube socket? The input jacks are shielded cliff type.
~Phil
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it's only somewhat bad at the main input,
what happens with nothing plugged in?
Could this be the shielded cable from the input jacks? A bad input jack?
That's where I'd start, if it's at the input, it only gets worse with amplification :laugh: