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I have a 1972 fender super 6 that has a problem. The amp sounds great clean but when I turn the reverb knob it has a high pitch squeal, the further you turn it the louder the squeal gets. It will also squeal with the tank unpluged. I checked the tank and it has no broken springs and seams to be fine,I also changed the reverb pre amp input and output tubes(12at7 and 12ax7)which did nothing to fix the problem. Can anyone give me a sugestion what else might be wrong with the amp?
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Can you test the tank with an ohmmeter? Even though the springs are fine, the little coils or the wires that attach to the RCA jacks can often break.
Also make sure that the RCA tank cables are good and that the ends are clean and tight fitting. -
Does it squeal when you have the reverb footswitch engaged in the 'OFF' position? That will ground the input grid for the reverb return tube.
The reverb return tube & the mixer gain stage make-up tube share the same cathode resistor & cap. My first thought is that there is a problem with that resistor / cap. Maybe a cracked resistor or solder joint? The solder joint makes more sense. A slight increase in the solder joint resistance could actually raise the gain of both stages as well as decouple the bypass cap from ground. That would allow signal to pass cathode to cathode between stages and possible create positive feedback through the mixer stage.
If the reverb return tube is oscillating, this would make perfect sense.
I may not have it 100% right ut I would defnitely check the cathode cap / resistor combo (and solder joints) first in this situation.Comment
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It squeals with the footswitch in eiither on and off position and also with the footswitch unpluged from the amp. I haven't yet taken the amp out of the cabinet but will do so to check for cracked solder joints/resistors/caps. Thank you for your help in this problem.Comment
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Good. That at least eliminates the possibility of anything being wrong upstream of the switch (like the reverb tank - even though I know you already adressed this).
The problem pretty much has to be somewhere between the reverb footswitch (tube grid) and the reverb volume pot (attached to that tube's anode). That's a pretty narrow area to concentrate on. I think you'll find it once you open up the amp.
ChrisComment
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Any solution
I have an amp exactly like you describe. V3 tested shorted on my tube tester. I cant find anything else bad but it still makes crazy noise when rev turned up. Did you ever fix your amp?Comment
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Is your amp in a high humidity environment such as a basement, 1972 ? If so let the amp sit out in the sun light for about 45 min with the sunlight beaming at the circuitry cards, Then try the reverb feature, some older fenders, I'm not sure when, are fabricated on cardboard composition cards, if so, the moisture causes weirdness after all else checks out ok.Comment
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Yes, I took the amp to an authorized Fender repair shop for an overhaul.The reverb driver cathode resistor was burned up and the power filter caps were vented(stuff comeing out). All power, bias, and cathode filter caps were replaced, all CBS mods were removed where applicable ( put back to Blackface specs). Modified to provide reverb on both channels.All switches,controls and tube sockets were de-oxed. All the tubes were fine ( I had replaced all the preamp tubes)All the power tubes were fine and were rebiased to the hottest ones. The amp sounds great, very responsive classic Fender tone and rich in harmonics that it never had before and more volume than I will ever need.Comment
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Glad to hear you got it working and are loving it. Thanks for being manly enough to use an amp that size and thus working to restore the natural order. See http://music-electronics-forum.com/t20524/
One of the reasons music has gone to hell these days is that we don't grunt enough as we move equipment. We are afraid to sweat, to do even five minutes of good hard physical labor.Comment
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When I was a kid, rockers came from industrial backgrounds. The day job was in a factory. We were manly men, manfully rocking manly amps in a manly way while wearing make up and fishnet and glitter.
Now the kids, if employed at all, are graphics designers "working" on each others websites and play twee little amps, but they dress like lumberjacks.
Whatever is this world coming to.Comment
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