Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: donahue on November 04, 2010, 07:43:59 pm
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Hi - a friend of mine has a Fender Super http://www.ampwares.com/amp.asp?id=102 (http://www.ampwares.com/amp.asp?id=102)
It occasionally cuts out while playing. Doesn't make a difference using a different cord. The inside looks good, no loose connections etc. What can cause this? My trouble shooting skills are novice at best but I can solder and open her up with out killing myself. It has (2) 6L6 power tubes and I believe the max dissipation is 19watts per tube so what kind of bias should I be shooting for? Around 30 watts?
Thanks for any tips you can throw my way.....
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Faulty volume pot?
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Yeah I guess I should start with that. Thanks! Gets me back into the way of thinking like when you use to able to work on your own car...start with the simple things first. The vol pot for the 2nd channel does have some scratchiness to it. When I get into the amp this weekend that will be my first check. Thanks again John..I hope that's all it is.
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Me too. It means I'd finally be right about something! :grin: The only thing made me think of it was an old SS amp I had, and the one treble pot messed up, gave the same result.
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> what kind of bias should I be shooting for?
The car's engine stalls. Do you check the tire pressure?
What John said and implied. works/cuts-out is usually CONTACTS in pots, jacks, and solder-joints. When it cuts-out, wiggle plugs and knobs, that usually narrows the search. If external excitement doesn't make it better/worse, let it bleed-down, open, bright light, and inspect the solder joints.
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Chopsticks are a useful tool for poking around inside an intermittent amp... which gives you a good excuse for Chinese food.
Pretty much everything you could ever want to know about servicing a Fender amp is located here:
http://www.el34world.com/schematics.htm#Servicing%20fender%20amps
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Thanks John, PRR & Butterylicious - I feel more confident delving into the little known now that you guys got me thinking on the correct path. The cut out is so quick,if it was any quicker there wouldn't be any cut out. I'll have to have someone play while I fiddle.
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Tell us what you find when checking the input and speakers jacks. And any other stuff you check.
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http://geofex.com/ > Tube Amp Debug Page > Intermittent operation
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Well got home from work today and started checking things out. 1st off the foot-switch was shorting out and the gain select switch didn't work all the time. Cracked solder joint on the foot switch jack probably caused by no outside jack nut. Soldered it back. Checked gain switch and it wasn't always switching. Sprayed a little contact cleaner into the push switches and checked continuity while switching. Seems to have cleared it. Speaker jack and speaker terminals seem fine.
Plugged in and started to play...sounded terrible even on the (clean) 1st channel. Slightly "bad" sounding distortion and "dis-harmonic" (is that a word?) . The amp had sounded halfway alright before. Maybe a bad tube? Disconnected the foot switch and plugged straight in, no change. Hope it wasn't from me spraying in the cleaner. When I wiggle the 2nd channel vol pot, it definitely makes lots of noise so there's another item. No noise when fiddling with the input to the amp, a little noise on a couple of other pots. I shut it down and I'm going to wait a bit and turn it on again and see if it sounds better.
Thanks a whole big lot for the links and tips. Hope I can get this thing sorted out.....