unclej Posted July 19, 2006 Report Share Posted July 19, 2006 the symptom: after this little peavey, a bravo 112, warms up it begins to make a sound like feedback only it isn't. it's a low pitch sound..approximtely a low g on a guitar. it does it with all the volume knobs tuned down. it's volume can be controlled only with the reverb control knob and once it starts it increases in volume by itself until it's too loud to stand. it does not seem to start on it's own but after a few minutes of warming up it will start once i pluck a string on the guitar. i know it's not feedback because once it starts it continues even after i unplug the guitar. troubleshooting so far: i've checked the electrolytics and replaced all of the tubes one at a time with known good ones to no avail. i've tested and cleaned all of the control pots and they seem to be functioning properley. before i started checking resistors and such i thought i'd see if one of you might have experienced the same thing and whether or not you think it could be a symptom of a bad reverb can. personally i'm still betting on a poltergeist. thanks for any help. john Quote Link to comment Share on other sites More sharing options...
mikhailgtrski Posted July 19, 2006 Report Share Posted July 19, 2006 replaced all of the tubes one at a time with known good ones to no avail. Sounds like a power tube starting to fail, except now you've gone and ruled that out. Quote Link to comment Share on other sites More sharing options...
unclej Posted July 19, 2006 Author Report Share Posted July 19, 2006 replaced all of the tubes one at a time with known good ones to no avail. Sounds like a power tube starting to fail, except now you've gone and ruled that out. actually i guess i didn't. i replaced the 12ax7's one at a time thinking it might be the one that controls the reverb and not knowing specifically which one it was. i didn't replace the power tubes so i'll try that in the morning. thanks. Quote Link to comment Share on other sites More sharing options...
mikhailgtrski Posted July 19, 2006 Report Share Posted July 19, 2006 It's kinda disconcerting the first time, if you don't know what's happening. If you let it go on, eventually the tube will die and you'll blow the HT fuse (assuming someone didn't replace it with too high a value ). Does it stop if you put the amp on standby? Quote Link to comment Share on other sites More sharing options...
spazzyone Posted July 19, 2006 Report Share Posted July 19, 2006 check the jacks to your reverb tank Quote Link to comment Share on other sites More sharing options...
mammoth guitars Posted July 20, 2006 Report Share Posted July 20, 2006 Does it stop if you put the amp on standby? Peavey Bravo does not have a standby mode, just on/off. Its probably a tube, there is not much in those things. There is a couple of opamps for the reverb tank and 5 tubes. Quote Link to comment Share on other sites More sharing options...
unclej Posted July 20, 2006 Author Report Share Posted July 20, 2006 thanks all.. mammoth's correct..no standby switch. thanks spazzyone...could be corrosion or something causing a weak ground i suppose. thanks again mikhailgtrski..i didn't get back to it today but i'll swap out the power tubes in the morning and let you know how smart you are. Quote Link to comment Share on other sites More sharing options...
mammoth guitars Posted July 20, 2006 Report Share Posted July 20, 2006 J, I have a Bravo schematic if you are so inclinded to troubleshoot with a scope. Quote Link to comment Share on other sites More sharing options...
unclej Posted July 20, 2006 Author Report Share Posted July 20, 2006 J, I have a Bravo schematic if you are so inclinded to troubleshoot with a scope. thanks for the offer but the first thing i did this morning was dig around until i found one new el84, popped it in and that fixed it so i just ordered a matched pair and that should take care of it. i really appreciate the help. john Quote Link to comment Share on other sites More sharing options...
Prostheta Posted July 20, 2006 Report Share Posted July 20, 2006 I was thinking more around your tank oscillating in sympathy with some part of your amp. Thing is, 60Hz or multiples thereof are actually closer to B than G. Good to hear your solution was cheaper and simpler. Not as cheap as simple as my car problems I bet!! Quote Link to comment Share on other sites More sharing options...
erikbojerik Posted July 20, 2006 Report Share Posted July 20, 2006 Poltergeist in my Peavey Sounds like the name of a garage band. Quote Link to comment Share on other sites More sharing options...
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