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 80's Series III x100 Problem View next topic
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BonesMachine
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Joined: 26 Aug 2015
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PostPosted: Thu Aug 27, 2015 4:07 pm   Reply with quoteBack to top

I bought this amp a few months ago and now i'm having a problem with it and was hoping to get some help on what's going on. The amp is an all original gray carpeted 80's series III (it doesn't say series III on it) x100 fixed bias 6L6GC.

After playing it for 5-8 minutes it will all of a sudden crap out and turn everything i play into buzzing distorted fart noises. If i continue to play it at this point it will blow a fuse. Playing the amp hard seems to make it crap out quicker. If i turn off the amp right after it craps out and then turn it back on it will play ok for about 30 seconds before crapping out again. The longer i wait after turning it off the longer it will play ok. I've tried disconnecting the reverb tank, playing all channels (rhythm, lead drive, hi lead), eq set to rhythm and lead. I also tried putting in a brand new set of power tubes and same problem. None of the pots are scratchy.

Before this problem the amp was suffering from slight low volume, early breaking up distortion and a weird note ghosting trail off sometimes . I did a little research and that stuff sounds like it needs new filter caps. Not sure if this new crap out problem is related. Any help would be appreciated.
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Brian D
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Joined: 19 Feb 2005
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Location: Oceanside, Ca.

PostPosted: Fri Aug 28, 2015 5:55 pm   Reply with quoteBack to top

While playing, look at your power tubes. If they start to glow red then the bias circuit needs checking (you already replaced the power tubes). That is just a start. It could be deeper but for now, eye-ball the power tubes.

added... one more thing to try. Remove the power tubes and with a toothpick, carefully tighten the pin tension in the tube sockets. The pin jacks could be stretched a wee bit not allowing a good solid contact with the tube pins (particularly pin 3 (plate) and pin 5 (control grid)).

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X100BNut
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Location: Hayward, CA

PostPosted: Mon Sep 14, 2015 11:55 am   Reply with quoteBack to top

It deserves a cap job. If you discharge the HV, you can measure the resistance from B+ to ground with a DVM.
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BonesMachine
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PostPosted: Mon Aug 14, 2017 11:56 am   Reply with quoteBack to top

turned out to be just a bad v3 phase inverter tube.
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