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Modular Amps
Egnater / Randall Modular Amps
UPDATED:Please HELP! My RM80 has Failed!
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<blockquote data-quote="kc2eeb" data-source="post: 110565" data-attributes="member: 811"><p>In my case I think the board was arching first. I would hear sounds that I mistook for computer or cell phone hash coming through either the ac line or the high gain preamp. I replaced the output tube 3 or 4 times (JJ 6V6s) thinking it was a bad run of tubes. Then, during a rehearsal, I played the amp louder than usual, and it finally arched enough to do the damage it did.</p><p>I measured the nominal dc impedance on all the OT leads and they seemed OK. So, the first repair attempt was to the original PA board. I did not reinstall it. Instead I ordered a replacement PA board from Randall as well as a new OT. I really would have to pull the old OT apart to see what's up with it since it doesn't read open or shorted. When I get time to, I'll open up the OT and maybe rewind it. As far as the PA board, I suspect the coupling caps to the PI are leaking DC which would raise the bias over the top.</p><p>The problem with the Randall pc boards is they didn't allow enough electrical clearance between the HV traces and ground on the original boards. That's why you will see some of the pc board material ground away on some of the boards. The HV short from the power supply connection to the board is fairly common.</p></blockquote><p></p>
[QUOTE="kc2eeb, post: 110565, member: 811"] In my case I think the board was arching first. I would hear sounds that I mistook for computer or cell phone hash coming through either the ac line or the high gain preamp. I replaced the output tube 3 or 4 times (JJ 6V6s) thinking it was a bad run of tubes. Then, during a rehearsal, I played the amp louder than usual, and it finally arched enough to do the damage it did. I measured the nominal dc impedance on all the OT leads and they seemed OK. So, the first repair attempt was to the original PA board. I did not reinstall it. Instead I ordered a replacement PA board from Randall as well as a new OT. I really would have to pull the old OT apart to see what's up with it since it doesn't read open or shorted. When I get time to, I'll open up the OT and maybe rewind it. As far as the PA board, I suspect the coupling caps to the PI are leaking DC which would raise the bias over the top. The problem with the Randall pc boards is they didn't allow enough electrical clearance between the HV traces and ground on the original boards. That's why you will see some of the pc board material ground away on some of the boards. The HV short from the power supply connection to the board is fairly common. [/QUOTE]
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Modular Amps
Egnater / Randall Modular Amps
UPDATED:Please HELP! My RM80 has Failed!
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