Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: winterturtle on July 17, 2022, 12:41:45 pm
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Hello again all! Apologies for the many clueless questions. One of the last issues I aim to tackle in phase 1 of this project is noisy reverb. https://www.tiffe.de/roehren/u255r.gif
It sounds like a 60 cycle. I've swapped for a replacement presumed good tube no change. The oil filled capacitor has been replaced. The noise seems the same with the tank hooked up or unhooked so imagining upstream. The hum is directly related to reverb level. Using a known good other reverb tank it behaves the same.
I'm asking for general advice and wisdom again. I've read several related type threads but struggling to apply to myself.
Regardless happy Sunday!
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Picture of how the amp is built may help
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Thanks L! I have only found that odd .gif link (rare I see a static image in that format) and haven't figured out making images visible here haha.
I have a nice print out here at home -- just wondering what I should be checking? Ideally I'd like to be more strategic than moving through the full reverb circuit unsoldering and checking values along the way. Flying blind is one option -- but some insight on strategy would be great, if that's possible here =)
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Leave the reverb tank connected and check if noise changes by placing it somewhere else. Dont bolt it down, move it and hear what happens to the hum.
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Leave the reverb tank connected and check if noise changes by placing it somewhere else. Dont bolt it down, move it and hear what happens to the hum.
The unit in question is located beneath a factory cardboard sheath that is stapled down - was hoping to not need to disturb it.
I did place my chassis on top of a 1980 Twin Reverb with normal quiet working reverb and hooked into my chassis the result was the same reverb noise unfortunately. For argument sake I tried both orientations of the RCA and both had the hum present.
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Try switching the pan ends around. If the pan's (noise sensitive) output transducer is sitting right next to the PT, then EMF from the PT will couple into the output transducer (and all the noise will get picked up by the reverb recovery stage)