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Post subject: Amp experts, I need you! TRRI
Posted: Mon Jun 29, 2009 4:24 pm
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Hi everbody. My Twin Reverb RI doesn't sound to good lately. It seems like when its well warmed up is when it starts to act up. I can have nothing connected and hear some little scratchy sounds.

Now before I take it to an amp tech, I would like to check out the tubes. Seems the normal thing to do right? So I tap on all the tubes with a pen and the were all silent except two. The two with the arrows pointed at them below. The pen taps which were light sounded like pen taps on a high quality condenser mic. Does this seem normal for those?

Any opinions would be greatly appreciated.

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Post subject: Re: Amp experts, I need you! TRRI
Posted: Wed Jul 01, 2009 8:55 am
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Mr. New Dilemma wrote:
Hi everbody. My Twin Reverb RI doesn't sound to good lately. It seems like when its well warmed up is when it starts to act up. I can have nothing connected and hear some little scratchy sounds.

Now before I take it to an amp tech, I would like to check out the tubes. Seems the normal thing to do right? So I tap on all the tubes with a pen and the were all silent except two. The two with the arrows pointed at them below. The pen taps which were light sounded like pen taps on a high quality condenser mic. Does this seem normal for those?

Any opinions would be greatly appreciated.

Image


I'd have all of the tubes tested and rule that out before zeroing in on the other components.

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Post subject: TRRI
Posted: Thu Jul 09, 2009 9:45 pm
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Hello Mr New, The tubes that are pointed out should react more vigorously to any tapping, due to the previous gain stages and their relation to the power amp. If it is just a clear reproduction,no static or ringing, then it's fine. As for the scratching noise, have you tried moving each control pot when this condition is happening? Another thing that you might try before taking it in is to remove one pre amp tube at a time to see if that isolates the source of noise. It might be kind of tedious, because you'd have to get the amp up to the noise temp then shut it off, remove a tube, and heat the amp back up, check for noise, replace the tube if the arcing is still there, and repeat the process until the noise stops. This method can help identify the problem section, and a known good tube substitution may be all you need. Oh yeah, use a marker to reference the tube to the socket before removing the tube. You know, a line on the glass and the metal socket. Good Luck Art


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Posted: Thu Jul 09, 2009 9:55 pm
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Thanks for responding. I did go and buy one preamp tube and replaced the one that the first arrow is pointing to. It had gone badly microphonic a few days after I originally posted this post.

I have come to the conclusion though that this amp needs to be be retubed all the way through. Considering I picked this amp up from Craigslist it's history is a bit vague. I would rather change all the tubes and KNOW the tube history. May sound costly, but it will let me think clearer about any future problems.

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Post subject:
Posted: Fri Jul 10, 2009 4:29 pm
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Good idea. I would just replace all the preamp tubes first though. Save a few bucks. In my experience, which is not extensive, every time a power amp tube failed, the amp went totally crazy, popping and blowing fuses and such.

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Post subject:
Posted: Sat Jul 11, 2009 10:20 am
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I wouldn't use Groove Tubes. Just my opinion, but I never had any luck with them at all. They'd either rattle or go microphonic pretty quickly. I'd go with JJ's or Tung-Sol. YMMV


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