Electric Guitars/Tube amp problem.



I need you help and thank you in advance.

My 100 watts tube guitar combo-amp is 4 years old. It's never really been used hard on the road, no gigging, just a few times rehearsed with the band and all the time I used it for practice at my apartment.

It never had any problem but until about a few months ago it started to make some popping noise sometime when I used it, sometime it's quite loud and sometime it had some kind of microphonic squeal noise also. I looked at the tubes when this happened and I saw the glow inside the tubes were uneven along with that popping noise but when the noise's disappeared the tubes glow are back to normal as well. This thing is unpredictable. Sometime it happened a few times when I used it(but only 5-10 seconds each time then stop). Sometime's not happened at all.. I used it everyday and not everytime it happened. THIS HAPPENED ALSO WHEN THE AMP WAS TOTALLY UNPLUGGED.

Just today, I accidently dropped a tiny screwdriver on the amp and it made a short nasty microphonic squeal noise. I tapped the amp lightly and it made the same noise each time I tapped the amp almost anywhere on it. It's very loud and sounds like when you make a wrong cables connection to an amp it's a nasty sound like that, but then it stopped shortly. And again this happened even when the amp's unplugged or volume's turned to zero.  

At the first place I thought it's the tubes that's reaching its ages. But now I'm not sure and I rather hope it's the tubes because I don't want that it has any major problem inside it. I've never made any mistake to it, it's never dropped or hit by anything. And without that noise sometime it still worked just great as normal.

I hope you can troubleshoot and find a solution to solve it.
Thank you so much!

Best regard,

ANSWER: Hi Izzy, what you describe is result of about all the problems an amp could have. I do not think you have a bad thing going on, just one of those thing that is a real pain to find. I will give  you some simple fix steps. Two things you told let me thing it is a bad connection and or dirt  in in the potentiometers, often called pots. They are the units that control tone and sound level. These have three wires coming from them. They all should be looked at, tugged and inspected on all ends. Loose wires can cause the noise you are getting, the power wire mostly and red. For cleaning these I use a Radio Shack product part number 6404315-1 and I clean all parts about every six months.  It works great and will not harm plastic, that is very important. Some melt plastic parts and wire coating.
The next thing I would do is re-seat the tubes. Remove them and clean off any dirt or oxidation. Please be sure the system is powered down, I had a small amp blow up seconds after I unplugged it, that was months ago and I am still finding parts. If you have a back up set of tubes now is the time to test the sockets and wiring.
The chance of a bad capacitor or a loose one is very good.
The things that you pointed out leaves so many places that could cause the problem. Heat and movement and the fact that it is intermittent makes it very hard to pin point. I would send you a diagram but I was not told the make. I you look it up on Google they should have a diagram. Please let me know how things go, I want to be of as much help as I can, so write back as many times as it takes.
Thanks and I will be waiting to hear from you Izzy!

---------- FOLLOW-UP ----------


I'm very deeply sorry about had not responded to your massage earlier. I had to be away on my vacation for a while.

Thank you so much for your very useful help and suggestions, especially about maintenancing the amp. I haven't had much experience with tube amp and it seems that this baby requires lots more care and knowledge than I thought.
However, about my amp. All those problems have just disappeared itself. I didn't do anything to fix it. It hasn't had any further episode at all after many times I played. Well at least it hasn't for now..
I have no idea what caused that before but I'm using it everyday just like always and I'm feeling pretty good that I almost forgot the problem earlier. Thank you again for your help and if I need other further question I'll return to you immediately.

Best reguards,

I am happy to hear all is fine! I only wanted to know if things are OK. That is a good report.
I love tube amps but they can get out of sorts some time. I have an old Vox AC30,25 years old if a day. I Replace all the tubes if one goes. I stay stock, I never second guess a Vox or Fender engineer. I am an engineer and I would not people second guessing my work.
I am here for minor or major problems. I do thank you for letting me know all is fine.
Izzy take care!

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DR Kevin P Moore


Guitars and cats make life so much better. Playing the guitar is a wonderful thing, fixing you guitar is not that hard. I have played since I was a kid and started to fix guitars and the other things that needed repair. I still repair guitars for friends and myself and do enjoy it. I rebuild old guitars to their former condition, all amps and music gear. That the mystery out of where and when a guitar was made. The value of it and the difference between junk and a guitar you can grow old with. Ask me things and have some fun.


The fascination with electric guitars is the top for me. I fix amps, wiring and put the things that fall off back on. The way to really set a guitar up and make it a player. Buying a guitar is an art, and good amps that will get out that tone we all look for, Zen guitar and amplifier is a way to approach it. Better is no worry ask an expert.

Library of congress, five patients. I write on several guitar forums and many essays on guitar health.

PhD, MS, BA and a BS all from CMU. I have a BA from Mercyhurst College.

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