Members manvspig Posted October 18, 2014 Members Share Posted October 18, 2014 A few days ago I had this problem: if I turned my pre-gain up to about 7 on my lead channel, the amp would make a sound that sounds like feedback. It wasn't normal feedback though. I could completely unplug the guitar from the amp and the noise would continue. The noise would also get louder or quieter as I turned the post volume knob up or down. It sounded like the noise was generated in the pre-amp somewhere, before the phase inverter. I didn't care to much because I can't imagine ever using that much gain. I've tried changing all the tubes except the power tubes and no luck (maybe I missed one? I will try again...) But today, the amp started making the noise on my clean channel. I switched from channel to channel and the noise continued. The guitar tone got much more distorted than usual during this event. I was also playing very quiet at the time. I turned off my amp. When I turned it back on to diagnose it, the sound had stopped (although if I turn my gain past 7 on the lead channel, it starts again temporarily. This is the same problem I was having a few days ago.). I have no effects plugged into my amp either. The amp seems to be making a bit of an "airy" sound right now (though that might be normal... haven't paid that much attention to it before...). I have modified the bias on the amp. I don't see why that would cause the problem. That's the only modification I've done to the amp. Any ideas? Link to comment Share on other sites More sharing options...
Members WRGKMC Posted October 19, 2014 Members Share Posted October 19, 2014 Sounds like you have a preamp tube going microphonic. Try tapping on the preamp tubes (lightly) with the amp on. Any kind of ping or static noise heard means they are going bad. It could be a loose tube in the socket, but any doubts, just change them. Link to comment Share on other sites More sharing options...
Members manvspig Posted October 19, 2014 Author Members Share Posted October 19, 2014 I've already tried changing each tube individually with a different tube that I know works. No luck. So I don't think it's a tube. Link to comment Share on other sites More sharing options...
Members manvspig Posted October 19, 2014 Author Members Share Posted October 19, 2014 Problem solved. I took the amp out of the box to make sure there was no bad solder joints and no loose wire. Couldn't see anything. I turned the amp back on and the squeal was less prominent. So I poked around a bit more and found that as I wiggled a wire, the squeal would change. I just put the wire where it doesn't make the noise. The wire was probably to close to a capacitor or something. And it's terrifying poking around in an amp while it's on... I'm used to having the caps discharged so this made me uneasy. I used a long chopstick to do all the poking. Link to comment Share on other sites More sharing options...
Members onelife Posted October 20, 2014 Members Share Posted October 20, 2014 I used a long chopstick to do all the poking. It's also a good idea to put your other hand in your pocket. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted October 21, 2014 Members Share Posted October 21, 2014 It's also a good idea to put your other hand in your pocket. Yup, one of the first lessons you get as a tech being trained working around HV components. never let the second hand be grounded. Another good suggestion is not to lean up against a metal work bench. I had a teacher who did that working around a flyback transformer in a TV and got zapped with 15KV in the shorts. Doesn't do allot for your love life. Link to comment Share on other sites More sharing options...
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