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Amp Stuff => EZ Board postings => Topic started by: Geezer on June 18, 2005, 06:18:07 am
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Hoffman Amplifiers
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> microphonic wires in Twin Reverb
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eanderso22193
Junior tube assistant
Posts: 97
(4/5/04 1:51 pm)
microphonic wires in Twin Reverb
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So I've got this Twin reverb I've been working on for some time. Its insanely quietert han when I first got it, but the final, and most perplexing problem, seems to be the noise in the reverb circuit. If I turn up the reverb pot, even with no tank connected, I get a bad hum...sounds like 60 Hz or a mutiple of it. If I tap the wire coming from pin 7 of the third 7025 tube I can hear the tapping loud and clear. This wire happens to travel under the board to a few resistors and a cap in the circuit before the PI, so I can't really see what's going on with it. Could this be a grounding issue? What causes wires to become microphonic? Would installing a shielded wire here help? Thanks.
Eric
ganzonimx
Hey get your own solder
Posts: 458
(4/5/04 5:46 pm)
Re: microphonic wires in Twin Reverb
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look for bad/coold solder connections.
Cris
PS: there are probably also other reasons...
eanderso22193
Junior tube assistant
Posts: 98
(4/5/04 7:38 pm)
Re: microphonic wires in Twin Reverb
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Yeah, I think I've resoldered everything in that section of the circuit at least once. Perhaps I'll completely undo everything and then redo it all.
Eric
tubejunky
Posts: 15
(4/5/04 8:02 pm)
Re: microphonic wires in Twin Reverb
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Try installing a .002uf capacitor and a 1m resistor in series from pin 1 to pin 2 of the reverb driver tube socket.
Funkalicousgroove
Junior tube assistant
Posts: 43
(4/7/04 11:11 am)
Re: microphonic wires in Twin Reverb
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I'm having a similar problem, I don't see what a local feedback loop would do to correct this, the hum comes from the recovery stage, I have the same wire that makes noise as well. The solder joints are good on both ends. the only thing I can think of is that the wire connecting the two grids is too close to the filament, but you can only get it so far away..
tubejunky
Posts: 16
(4/9/04 7:00 pm)
Re: microphonic wires in Twin Reverb
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You guys ever get this figured out?
Funkalicousgroove
Junior tube assistant
Posts: 57
(4/12/04 2:55 pm)
Re: microphonic wires in Twin Reverb
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Nope, I'm perplexed, My amp is on the thread marked Bus bar and single point ground. Any Ideas are appreciated
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