Old 50 caliber, volume fades in/out

[GE6550]

Hey everyone,

New to the board, looks like an amazing source of Boogie expertise.

I picked up my first Boogie today - an old .50 caliber, quartet of EL84 power tubes (even says "Class A" on the back, I really doubt that), 5 12AX7s, metal rocker switches on the front panel.

I plugged it in, let the tubes warm up for a few minutes - took it off standby, and started playing. Sounded great for the first 3 minutes - then the volume started to slowly fade in and out, almost like a tremolo effect at a really slow speed.

Anyone have a similiar problem, or know of a possible fix?

Thanks.

 

[plumptone]

If it's old, and you don't know how long the tubes have been in there, I would start out with that. Either check them one by one with a known good one (both output and pre amp tubes), or just retube the thing. It may be a bit pricey, but could be well worth it. Eurotubes sells a full replacement set at a decent price, and the turnaround is fast.

I'm not a tech, and I'm sure others will chime in on this, but I know folks like to have their caps looked at if the amp is over 10 years old. Yours is definitely at least 10 years old by now I would think, so that's something else to consider.

 

[rvschulz]

mine is a 6L6 so it may not be exactly the same problem. However, when mine does that I know one of the power tubes is not seated correctly, it may be slightly unseated. it is possible that one of the power tubes or the sockets is not too good.

if it is still running original tubes, an investment in new tubes will really bring it to life. of course, that might not be the problem, but will get the most for your tonal qualities.

 

[GE6550]

Thanks everyone. I've ordered a new set of Mesa tubes, hopefully they will do the trick (previous owner mentioned changing the EL84s every 4 months!)

 

[mernin]

This happened to my amp the first time I used it (ebay special)
I read online here to try a jumper cable bypassing the effects loop, just plug the output into the input of the loop. I think the cause is dirty jacks?
any way that fixed it.
Hope this helps and I love this amp.

Terry Mernin
San Pedro, CA

 

[GE6550]

Cool, once I retube it I'll try that trick with the jacks (never would have guessed that).