Microphonic output tubes?

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stratavox
Junior tube assistant
Posts: 27
(2/23/04 6:24 pm)
 Microphonic output tubes?
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 I think we've touched on this before but... my 5E5 Pro build has a pair of Ruby 5881's that are 7 months old. I play at 4-5 on volume, two or three nights a week every week, so I feel I've gotten my money's worth from them. I just opened up the amp for a "one year check-up", and found that I can tap the power tubes with no pre amp or phase inverter tube installed, as well as the chassis and various items on the board itself, and hear it VERY clearly through the speaker. Normal? TIA for any input...
 
GroundhogKen
Forum Moderator
Posts: 2295
(2/23/04 9:05 pm)
 Re: Microphonic output tubes?
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 I'm not sure it's "normal", but it's certainly not unusual.

All tubes are microphonic to some degree. Install a new pair and see if they're better, worse or the same.


Ken
 
stratavox
Junior tube assistant
Posts: 28
(2/24/04 8:30 pm)
 Re: Microphonic output tubes?
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 Hi Ken-anyway, I replaced the output tubes with a fresh set, and the noises are gone, with one exception. The unshielded wire that runs from the end terminal on the volume pot for the bright channel to pin 2 of the p/i tube is still very sensitive to touch- static if you put a finger near it, and an audible "thump" if you tap it with a probe. Continues after a swap....the Ruby power tubes are 7 months old, so I really don't mind a swap, but that one wire to the p/i tube tasks me...thoughts anyone?
 
6G6
Junior tube assistant
Posts: 92
(2/24/04 9:24 pm)
 Re: Microphonic output tubes?
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 Umm, don't touch it?
 
 
GroundhogKen
Forum Moderator
Posts: 2299
(2/24/04 9:48 pm)
 Re: Microphonic output tubes?
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 Make sure the wire isn't connected to a loose terminal on the pot or the tube socket. Try to determine if the pot end or the socket end of the wire is the source of trouble--could be a bad pot if the wiper isn't making good contact with the resistive material. Maybe a tube socket pin is loose or needs retensioning.

Try a shielded wire. Secure the wire with a tie wrap.

Ken
 
stratavox
Junior tube assistant
Posts: 29
(2/25/04 5:59 am)
 Re: Microphonic output tubes?
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 Thanks Ken, appreciate the input.
 
 
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