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Potential Amp Problem?


peacemaker

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Posted

My Twin is hissing a lot more than usual with a borderline high pitched howl. At one point, it would do that high-pitched howly thing big time, and I had all the caps replaced and a couple other mods. Black-faced innerds in a silver-face package. Anyway . . . that was several years ago and it's been perfect. There's also this tinkling sound going on. Sounds almost like cracking glass. Makes me afraid to touch it. This amp has travelled a little bit, so I'm wondering if something has gotten knocked loose or I've got a tube going out . . . thoughts? I'm not an amp guru, so thought I'd ask some . . . I just love my Twin! :D

Posted

Sounds like a microphonic tube. One thing that can help pin point microphonic tubes is tapping them with a chopstick. It's not a perfect science, but often the offending tube(s) become immediately apparent. Another thing to try is cleaning your tube socket. Get some Caig DeOxit and spay the socket and/or pins of the tube and then seat and reseat the tubes several times the clean the sockets.

Posted
Sounds like a microphonic tube. One thing that can help pin point microphonic tubes is tapping them with a chopstick. It's not a perfect science, but often the offending tube(s) become immediately apparent. Another thing to try is cleaning your tube socket. Get some Caig DeOxit and spay the socket and/or pins of the tube and then seat and reseat the tubes several times the clean the sockets.

 

Agreed. Even tapping it with your finger should work. If you use any electronic cleaner spray on tube sockets or input jacks, be sure it has no lubricant.

Posted
Agreed. Even tapping it with your finger should work. If you use any electronic cleaner spray on tube sockets or input jacks, be sure it has no lubricant.

True. That's why I mentioned DeoxIT and NOT FaderLube. Looking at their website it appears there have been some name changes (again) and all the product appear to carry the DeoxIT name. Make sure the get the contact cleaner and NOT the lubricant.

 

MG chemical also makes a good contact cleaner.

Posted

This takes me back to when my old Dual Showman would have tube issues. And yes, you could find the culprit fairly quickly, most times, with that technique...

 

 

knock on wood , I haven't had these issues in a while.

Posted

So . . . One of my pre-amp tubes (those are the little ones, right?) sounds like tapping on a microphone when I tap it with a chop stick as advised. I've never tapped my tubes with a stick, so I don't know how that is SUPPOSED to sound. :lol: But, none of the others make any real noise through the speaker when tapped, and this one does. It doesn't tinkle or squeal or anything. Just sounds like tapping on a microphone. Is this normal, or have I found a bad tube?

 

Thanks for all the advice guys! :D

Posted
So . . . One of my pre-amp tubes (those are the little ones, right?) sounds like tapping on a microphone when I tap it with a chop stick as advised. I've never tapped my tubes with a stick, so I don't know how that is SUPPOSED to sound. :lol: But, none of the others make any real noise through the speaker when tapped, and this one does. It doesn't tinkle or squeal or anything. Just sounds like tapping on a microphone. Is this normal, or have I found a bad tube?

 

Thanks for all the advice guys! :D

 

By your description, I think you've found the culprit!

Posted

Ok. Now which one is it? Starting from left to right looking at the FRONT of the amp; V1 is the first preamp tube and V6 is the one closest to your power tubes.

Posted
Ok. Now which one is it? Starting from left to right looking at the FRONT of the amp; V1 is the first preamp tube and V6 is the one closest to your power tubes.

 

It's V1 . . . implications?

Posted

Try switching V1 with V5. If V5 is quiet in the first position, leave it there. V5 is a "function" tube and no noise will show up using the noisey V1 tube there.

  • 4 weeks later...
Posted

Alright . . . been a while since I got the advice and things have been crazy. I just spent a few minutes tinkering. Here's what happened:

 

Switched V1 with V5 as advised. Still had microphonics showing up. Seemed like V2 was the culprit. Figured I'd mis-diagnosed & went back to status quo.

 

Switched V2 with V5. Microphonics still showing up. Reversed that.

 

Switched V1 with V5 AGAIN & will live with what I've got for the time being. Ugh . . .

 

Seems like I've got at least 2, maybe 3 microphonic tubes!? Wha? Methinks it's time for a pro . . .

Posted
Alright . . . been a while since I got the advice and things have been crazy. I just spent a few minutes tinkering. Here's what happened:

 

Switched V1 with V5 as advised. Still had microphonics showing up. Seemed like V2 was the culprit. Figured I'd mis-diagnosed & went back to status quo.

 

Switched V2 with V5. Microphonics still showing up. Reversed that.

 

Switched V1 with V5 AGAIN & will live with what I've got for the time being. Ugh . . .

 

Seems like I've got at least 2, maybe 3 microphonic tubes!? Wha? Methinks it's time for a pro . . .

 

 

Just a silly thought, but the last work done on this amp was years ago? Could it be that you have tubes that are several years old in your preamp that all have lots of hours and on/off cycles on them?

 

Often huge numbers of on/off cycles in tubes and the expansion/contaction cycles the tube guts go through will cause things to loosen up, and then add the vibrations induced by speakers in that powerful amp and you do have a recipe for microphonics to begin... Especially if that amp is the only one you play through on a regular basis.

Posted
Alright . . . been a while since I got the advice and things have been crazy. I just spent a few minutes tinkering. Here's what happened:

 

Switched V1 with V5 as advised. Still had microphonics showing up. Seemed like V2 was the culprit. Figured I'd mis-diagnosed & went back to status quo.

 

Switched V2 with V5. Microphonics still showing up. Reversed that.

 

Switched V1 with V5 AGAIN & will live with what I've got for the time being. Ugh . . .

 

Seems like I've got at least 2, maybe 3 microphonic tubes!? Wha? Methinks it's time for a pro . . .

 

I had the same problem with my DRRI a few months ago. I reversed the VI and V5 tubes as advised and dramatically reduced the hissing. Like you, I had never plunked around the innards of a tube amp and was pretty nervous. But it was easier than I had feared. Just stay away from the power tubes.

 

If you've got multiple tubes going though, you might want to get a new set.

 

Best of luck

Posted

Some of you guys may know about this site, lots of pro and amateur amp techs here. Friendly site to get answers for amp questions or advise. Helped a lot when I restored / blackfaced my old silverface Twin. Also a link there for a huge number of archived amp threads.

 

http://music-electronics-forum.com/

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