Tweet
This is my first post, so of course it's about a jcm900. Because these amps were made basically to be problematic, as far as I can tell.
Anyway, thanks in advance if anyone can help me with this.
Problem: jcm900 4100 head--when on the clean channel, A, there is no treble/presence response whatsoever, and it's woofing. However, on the high gain channel, B, everything sounds exactly how it should sound.
Plate Voltage is 474. Tubes (el43) are running at about %60, highest at 31mA.
Tried playing around with preamp tubes and no change. So the preamp tubes and the sockets are all working.
Didn't see any bulging around the caps, and can't find any burn damage anywhere visible.
I've gone at the jacks and pots with Contact Cleaner and already tried jumping the effects loop--no change.
Again, this is only channel A. Oh, and the gain knob on channel A has no effect unless you bring it all the way up, and when you do that all sound completely dies out of the channel.
I hope I don't have to take the PCB boards out because they look fragile as all hell and I've never done it before. However, this amp when running right is worth maybe $400 and the cheapest tech I've talked to quoted me $300--so if I have to take the boards out, I will. And while doing so I'll wish all amps were hand wired with turrets, ha.
Anyone have an ideas? or do I have to pull the boards out?
Anyway, thanks in advance if anyone can help me with this.
Problem: jcm900 4100 head--when on the clean channel, A, there is no treble/presence response whatsoever, and it's woofing. However, on the high gain channel, B, everything sounds exactly how it should sound.
Plate Voltage is 474. Tubes (el43) are running at about %60, highest at 31mA.
Tried playing around with preamp tubes and no change. So the preamp tubes and the sockets are all working.
Didn't see any bulging around the caps, and can't find any burn damage anywhere visible.
I've gone at the jacks and pots with Contact Cleaner and already tried jumping the effects loop--no change.
Again, this is only channel A. Oh, and the gain knob on channel A has no effect unless you bring it all the way up, and when you do that all sound completely dies out of the channel.
I hope I don't have to take the PCB boards out because they look fragile as all hell and I've never done it before. However, this amp when running right is worth maybe $400 and the cheapest tech I've talked to quoted me $300--so if I have to take the boards out, I will. And while doing so I'll wish all amps were hand wired with turrets, ha.
Anyone have an ideas? or do I have to pull the boards out?
Comment