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Old 16th January 2011, 05:31 PM   #21
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6922 is a twin triode similar to a 6DJ8
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Old 16th January 2011, 05:40 PM   #22
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Location: Alps:Tube amp designs over 150W, SMPS guru.
Quite right.....Apologies my error. I was thinking of another.
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Old 18th January 2011, 05:50 AM   #23
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Just as a thorough follow-up, there was bad news and good news: bad news was that the problem re-occurred after I put the original coupling caps back in (yes, with insulated leads). I checked all components again, but this time I took a peek on the other side of the board (hard to do since the top is not easily removed). I saw that solder from the coupling caps melted below into wiring from OPTs and the two were in contact. I've insulated the wire and everything is back to normal. Unfortunately I can't move the wire the way it's designed, so this was an accident waiting to happen.
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Old 18th January 2011, 10:55 AM   #24
DF96 is offline DF96  England
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After soldering always do a visual check before switching on. Always use the right amount of solder - too little gives a bad joint, too much can also give a bad joint and shorts to other things. As far as possible, don't carry solder to the joint on the iron as this wastes the flux so you try to compensate by adding more and more solder to recover the situation.
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Old 26th January 2011, 11:15 PM   #25
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Okay, it seems that I must have damaged something with the red plating: After warm up one channel is consistently a little louder than the other, and when I power on the amp the weaker channel (R) makes little popping sounds for a few seconds. I also notice the output tube socket that redplated sometimes will not allow me to increase the bias pass a certain point. The other sockets bias fine. Otherwise the amp is performing well. Does this sound like a bad cathode resistor? or cap?

The schematic on page 1 for the bias circuit seems fairly accurate with the exception that there's now one per output tube.

Last edited by wushuliu; 26th January 2011 at 11:24 PM.
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