Uh oh... Should I be worried? SOLVED (or, I am an idiot)

[csweldon]

I took my RM20 out for it's inaugural gig last Saturday night, and it performed like a CHAMP! (not the amp, Champ, but like a champion haha) 3 hours of music, running fairly loudly. It really sat well in the mix and it had edge without being fully distorted - pretty much exactly what I was hoping it would do 8)

A few busy days later and I was able to fire her up again. Switched on, let the tubes warm up, dig into the strings and... Wait, that's not right; it was making almost static noises, a couple popping noises. It's bass response was dramatically lower than before, and if I hit the low strings hard it kinda had a short pop/burst of sound, and then would decay with little sustain. I could still get it fairly loud, and the high notes could still ring out. It's almost like it's been neutered, if you know what I mean.

My limited experience with tube amps tells me that it's probably preamp tube related, and I have a fresh set on the way to go in. It was a used amp, so it's not unreasonable to think they could be ready for a change. Still, I'm compulsive and need to investigate while I eagerly await my new hot bottles of ROCK.

So, I guess what I'd like to know is - have any of you ever experienced this? If so, how did you solve it? Any insight any of you have would be truly appreciated!

 

[eedude]

okay perhaps a bad tube. Swap what you can and see. Have you tried removing the module and power the amp on to see if it still makes pops? Do you have a second module to try?

It's hard to diagnose remotely, but I did experienced pops in one of my Rm100's. The failure was "arc over" in the power amp section. Arc over is when the high voltage B+ arcs to ground in the amp. When the discharged occurs you get a pop out the speaker (at least I did). I was getting several pops per second. Others have experienced this arc over issue in the amp and on modules as well.

I don't know if that is your amp's defect, but it's worth considering. If the the arcing is occurring inside the amp (versus on the module) what you can do is remove the amp from the box. Set the amp so that you are looking at the guts. Connect it all up and power it on. IF the room is dim enough you should be able to see the discharges....

 

[warlok]

My very un-tech-like answer - 3 times now I've put power tubes in my RM100. EL34's when I got it used, EH 6L6's after a week or so, and now 2 weeks ago when I swapped to JJ 6L6's. Each time, I had a tube that would not bias correctly (voltage was jumping around). When I went to play, it was static and was popping intermittently. Cleaned the pins and sockets, swapped the tubes to different sockets, tried again, and they all biased and the sound was perfect. Maybe just re-seat or swap tubes around, and clean pins and sockets... Free to try...

 

[Mattfig]

Funny....But a little Deoxit and wiggling seems to solve 50% of people's MTS woes here....Maybe that's a high estimate? I have an idea...

Look out!

 

[csweldon]

Thanks, everyone. These all make sense, I have a good feeling that one of these will be the answer. My tube amp experience is still pretty limited, so this info is all really helpful!

 

[csweldon]

After assuming it was somehow tube-related, I switched out the tubes, rebiased and nothing had changed. I tried jumpering the effects loop, cleaning the tube sockets (hey, it should be done from time to time anyway, right?) I turns out the problem was SO very obvious. I'll give you a moment to guess...










Did you guess? Alright. If your guess was "input jack," then you are correct. In a fit of desperation, I started wiggling my input cable, and when I pushed down on it lightly my signal went back to the way I remember it: ballsy, full and all around beautiful! I pulled the chassis, pushed the pins inward slightly, cleaned it for good measure and now I'm back in business. Plus, I have an extra batch of tubes for when they ARE the issue :lol: I still may want to have it replaced at some point (professionally; it's one of those plastic-enclosed jacks and is soldered to the boost circuit board. A little above my skill level!) but right now things are working great!

Anyway, thanks again for your help, everyone. I really appreciate you taking the time to read and respond. Now, back to playing!