Hello everyone,
I just aquired one of these amps and I love it! Rich tone and of course, incredible gain. My other amp (Gibson Falcon RVT 19) is great at home but I was looking for something I can gig with. And this baby has WAY more bottom end and great tonal control.
I plan to use the clean channel mostly, with some effect, and then switch into high gain when I like.
Problem: the clean channel, after 5-10 minutes, suddenly loses output and low end, and gets crackly crunchy. I haven't replaced any tubes or anything yet, as I just brought it home the other day. I saw another thread about these amps, I wonder if anyone can give me some basic things to try before tearing it open. Could it be a burned out 6l6 or something that changes with heat?
Thanks,
axylotyl
I just aquired one of these amps and I love it! Rich tone and of course, incredible gain. My other amp (Gibson Falcon RVT 19) is great at home but I was looking for something I can gig with. And this baby has WAY more bottom end and great tonal control.
I plan to use the clean channel mostly, with some effect, and then switch into high gain when I like.
Problem: the clean channel, after 5-10 minutes, suddenly loses output and low end, and gets crackly crunchy. I haven't replaced any tubes or anything yet, as I just brought it home the other day. I saw another thread about these amps, I wonder if anyone can give me some basic things to try before tearing it open. Could it be a burned out 6l6 or something that changes with heat?
Thanks,
axylotyl
Sounds like leaky coupling caps. Check if your output tubes are glowing "orange" or "reddish" in color. If this consistently happens after 5-10 minutes, then I think that's the problem.
After the amp has been shut off and then you turn it on, does it work normally, then exhibits this problem 5-10 minutes later?
After the amp has been shut off and then you turn it on, does it work normally, then exhibits this problem 5-10 minutes later?
Hi JonSnell, the connections look ok, although the bus is noisey. It does fine with an MXR phase 45 inline to the input, but through the bus it's weak and snowy.
Poacher, you may be onto something there—it works fine, then 5 minutes in it does the thing I described, loses bottom and power. The tubes were glowing blue, a lot... I switched the standby switch on and off and this time it worked, although last few times it did not. I ran it for almost 30 minutes without the symptom this time. The tubes were not that blue glow, just faint orange at the base, like I think they should. I had to take off after that but will continue measuring times until it craps out again. Funny, it was doing it consistently until today. THANKS both of you for your immediate response and great advice.
btw JonSnell, although it was running fine, the effects bus is still trash—noisey and weak. Its horrible to have the one effect I tried though there. Does that give any new ideas?
Thanks!
Poacher, you may be onto something there—it works fine, then 5 minutes in it does the thing I described, loses bottom and power. The tubes were glowing blue, a lot... I switched the standby switch on and off and this time it worked, although last few times it did not. I ran it for almost 30 minutes without the symptom this time. The tubes were not that blue glow, just faint orange at the base, like I think they should. I had to take off after that but will continue measuring times until it craps out again. Funny, it was doing it consistently until today. THANKS both of you for your immediate response and great advice.
btw JonSnell, although it was running fine, the effects bus is still trash—noisey and weak. Its horrible to have the one effect I tried though there. Does that give any new ideas?
Thanks!
The FX loop causes trouble when NOT in use, so telling us some MXR works there doesnl;t answer the question.
The FX return jack has contacts inside that carry the signal on through when nothing is plugged into it. If those get dirty or oxidized then exactly your symptoms can result. An old trick is to plug a spare cord from FX send to FX return, creating a bypass.
However: you also report this only affects the clean channel? Is that correct? ALL channels run through the loop, so that would tend to point us elsewhere. The only part of the amp that is only used in the clean channel is V3B and associated smaller parts. So one triode, a few relay contacts, and some caps and resistors.
The FX return jack has contacts inside that carry the signal on through when nothing is plugged into it. If those get dirty or oxidized then exactly your symptoms can result. An old trick is to plug a spare cord from FX send to FX return, creating a bypass.
However: you also report this only affects the clean channel? Is that correct? ALL channels run through the loop, so that would tend to point us elsewhere. The only part of the amp that is only used in the clean channel is V3B and associated smaller parts. So one triode, a few relay contacts, and some caps and resistors.
Hello Enzo, thanks for dropping in. Yes, correct, only the clean channel becomes symptomatic: the bottom end drops out of the clean channel and the signal falls off. It loses volume and bass response, and clarity. The sound becomes weak, tinny and crunchy.... like a radio between channels. No power at any position of clean gain knob, it is like dead. Other channels seem unaffected.
I did bypass the FX bus like you suggested using 2 different known good cords; no change.
When I open it up, hopefully this weekend, will check V3B, the caps and resistors. I appreciate the advice. Can you (anyone) think of anything else I should check or replace while I'm in? I will definitely look at the FX bus. It is very weak and noisy also. Do you (or anyone) you know if the other channels should be running through the tone controls or not?
Thanks again to all who've responded.
I did bypass the FX bus like you suggested using 2 different known good cords; no change.
When I open it up, hopefully this weekend, will check V3B, the caps and resistors. I appreciate the advice. Can you (anyone) think of anything else I should check or replace while I'm in? I will definitely look at the FX bus. It is very weak and noisy also. Do you (or anyone) you know if the other channels should be running through the tone controls or not?
Thanks again to all who've responded.
Hello everyone, I've lived with this for almost a year for various reasons. Since then I've learned of 2 mods I would like to do when I open her up. One is to remove noise-suppression diodes to reduce fizziness (actually I'd like this to be switchable as I sometimes like the fizzy), the other is to rework a little circuitry to enable the EQ to work on all channels. My Question: Has any of you had any experience of this?
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