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Any done any work on these amps? I have one amp that one channel is louder than the other. All tubes check out. Funny, if I lift the amp while it is playing the amp distorts out. Put it back down and it goes back to playing at the same lower volume. Pins socks need tightening? Loose wire in amp?
Any suggestions would be appreciated!
Thanks!
Bill
Follow Ups:
What ever the number. They must love you at tube replacement time. Anyway, i worked on several sino amps where the transformer leads were improperly routed and one wire was caught between the trans body and the chassis. In one unit i manage to save it as the insulation did not break down and the other unit it shorted and took out the tranny. Just thought i would put that out there in case your hunt for a cold solder joint, which gets my vote, does not pan out.
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Have Fun and Enjoy the Music
"Still Working the Problem"
I'd remove each tube and clean the pins and sockets with a little contact cleaner. I like Caig Deoxit. Work the tubes in and out of the sockets to issue good contact.
You may need to tighten the socket tangs, if any have loosened-up.
anywhere inside the amplifier. Could be a lead that goes in and out of contact when you physically disturb the amplifier. This can be a "bear" to find, but you have to go inside and gently wiggle everything. (Power OFF, of course.) Eventually, the culprit will make itself known.
"you have to go inside and gently wiggle everything. (Power OFF, of course.) "
I would use an insulated tool to wiggle wires and components with power on and music playing. That's the only way to know when you've hit a sensitive area. Isn't this a Chinese amplifier? Geez, could be anything. Probably needs all the tube sockets replaced as a start.
--------------------------
Buy Chinese. Bury freedom.
but I did not want to be the guy who told the guy to wiggle parts with power on, if the guy got electrocuted.
I have a pair of Beveridge direct-drive amplifiers, which are now 46 years old but which I have owned for about 4-5 years. For the first year or so of my ownership, one of them would tend to oscillate even on the work bench, with no speaker attached. (In fact, you can't practically work on the amps while they are attached to the speakers.) Since those amps develop 3200V in the output stage, I was loathe to do as you suggest. I could only power it up, determine that it was or wasn't oscillating, and then power down and wait for the V to settle before touching anything. Using that approach and with the kind and patient email advice of Steve O, we practically rebuilt the amplifier section by section, as each fix failed to affect the tendency to oscillate. Finally I said to myself that the problem must be something illogical, because we had covered all logical possibilities. At that point, I went around wiggling parts (not for the first time), whereupon I discovered that one capacitor had a bad solder joint that gave way under my second or third wiggle. I had empirically re-soldered most of the joints on the PCB before that, to no avail, among the many other things I/we did. This wasn't a wasted effort, because I learned a lot about the complex Beveridge circuit.
Ya, I think it is. They said that they improved the QC. I haven't taken it apart yet. We'll see.
Bill
IME, RoHS solder is hard to get right, on thin PCB boards. Many new guitar amps suffer weird maladies, until you suck up the OEM stuff and solder all points with 60/40.
Pain in the rear... but, much of the random issues stop after the fix.
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