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new valves to cut feedback


JimH

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I was at band practice last night and I was feeding back pretty badly - I use a 20W plexi type thing, turned about halfway up, using the treble channel with the low input. It's not like it was a really excessive overdrive or anything.

 

I'm thinking maybe I need new valves?

 

Any recommendations for this sort of amp

(I'm in UK)

 

Cheers.

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does it feed back with difference guitars and pickups?


unpotted pickups feed back..hell, even some potted pickups feed back.


Tap your preamp tubes with a pencil..if you hear the "tink" sound, that would mean a microphonic tube, and the main culprit in the feedback problem

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Yeah it's all guitars and all pickups. I'm just wondering if lower gain tubes or tubes with lower microphonic properties might help. I don't know the history of the tubes, they may have been in a while - although the amp was kind of NOS - which implies they didn't have all that much use.

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Originally posted by JimH

Yeah it's all guitars and all pickups. I'm just wondering if lower gain tubes or tubes with lower microphonic properties might help. I don't know the history of the tubes, they may have been in a while - although the amp was kind of NOS - which implies they didn't have all that much use.

A lower gain V1 would be similar to just lowering your amp's gain.

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Check your cord too. I had a microphonic cord that was causing me problems.
As for tubes, a microphonic tube will cause feedback. Try turning your amp on but don't plug in the guitar(no guitar, no cord). Turn to volume up all the way. A bad tube will start to squeel. Tape on top of the amp and listen for unusal noise. You can also tape on the tubes with a pencil.

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Originally posted by tlbonehead

Did you miss the part about it feeding back with all pickups/guitars?

 

 

Oops, I did read that but thought that he meant that the problem was "all guitars and all pickups", not that the problem occurred with all guitars and all pickups.

 

I think my brain broke.

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Originally posted by poosis



Oops, I did read that but thought that he meant that the problem was "all guitars and all pickups" (i.e. due to those factors), not that the problem occurred with all guitars and all pickups.


I think my brain broke.

 

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Cheers - Poosis, all suggestions welcomed with open arms - no matter how bizarre!;)

Cheers guys, looks like it's pencil tapping time.

Incidentally is:
- V1 - first gain stage
- V2 second gain stage
- V3 phase inverter.

?

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Originally posted by GTM

Check your cord too. I had a microphonic cord that was causing me problems.

As for tubes, a microphonic tube will cause feedback. Try turning your amp on but don't plug in the guitar(no guitar, no cord). Turn to volume up all the way. A bad tube will start to squeel. Tape on top of the amp and listen for unusal noise. You can also tape on the tubes with a pencil.

 

 

1+ I had a bad cord and it was causing terrible feedback. Also for a while I had it another time and the input jack on the amp was a little loose and was causing it. Point of the story is that it seems almost everything causes feedback so leave no stone unturned!

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