RM50 Issues

[deedub]

At a recent gig, while loading in my gear, my RM50 head took a short, sliding ride to the floor... slid about 6 inches off a Rack and Roller cart, and impacted the floor. Nothing serious, I thought.

Ever since, I've been having some issues. I run a Blackface module for clean and a Plexi for crunch. The Blackface module will NOT get clean, and the Plexi module now gets squealy REAL fast. I've pulled all the tubes, and checked them while the amp is on.. glow looks good, no burn spots.. so I don't think it's the tubes (power or pre).

Are the multi connectors in these amps secure? Should I pull the chassis and make sure everything is plugged in tight? How do I spot a cold solder joint? This is my only amp, and I've got too many gigs to leave it in a shop for 2-3 weeks!

Any insight/help/advice you can give is much appreciated!

 

[shred-o-holic]

Have you swapped preamp tubes in and out? I had some squealy issues with my first RM 100.......Bruce Egnater fixed it and said that my chassis was slightly bent which was causing the problem....may have happened in your case as well?

 

[deedub]

I swapped preamp tubes in the Blackface module, because that's where I initially noticed the problem... cleans not "clean".

I'm going to pop the chassis out of the shell today and check all the ribbon/multi connectors to make sure everything's plugged in tight... if that doesn't help, tube replacement will be next. Just because they look good, doesn't mean that they are!

 

[JKD]

What about pre-amp tubes in the chassis?

The one closest to the input (furthest away from the back)...the initial signal passes through there before hitting the module.

After a drop like that, all tubes are suspect IMO.....you can go with the pencil test for microphonics but that still won't tell you if they're passiing a signal properly.

 

[deedub]

Well, I decided to play it cautious and dropped it off at the only local place I trust to work on tube amps. They have worked on some of the Randall modular stuff before, so they should be able to track it down.

 

[shred-o-holic]

What about pre-amp tubes in the chassis?

The one closest to the input (furthest away from the back)...the initial signal passes through there before hitting the module.

After a drop like that, all tubes are suspect IMO.....you can go with the pencil test for microphonics but that still won't tell you if they're passiing a signal properly.

Yeah precisely......that's what I meant as well..

 

[deedub]

Turned out to be faulty output tubes. Lesson learned.. just because the tubes look fine doesn't mean that they are!

The tech said he was less than impressed with the track record of the JJ's that were in there.. replaced them with Ruby's. What are you guys running in yours?

 

[deedub]

****... first time firing up the amp after I picked it up from the shop. They put in new TAD output 6v6's, but I'm not sure they checked out the whole amp. Clean channel is still WAY to fuzzy/overdriven/compressed sounding... when you hit a string hard, it compresses and sounds way fizzy. This is driving me crazy!

So... next thing will be changing out all the preamp tubes in the chassis itself. Failing that, I guess the chassis and all pc boards will have to get a thorough going over.

Not happy with the electronics shop at all. I don't think they checked out the amp... just the power tubes.

 

[Shinozoku]

If your Blackface isn't clean, maybe it's one of the old models that were defective. If so, check this out:
http://www.grailtone.com/guitar-tone-articles/randall-modules-clean-modifications.html

EDIT!!!: Gah, didn't read your post thoroughly. My bad

 

[Jaded Faith]

If they put 6V6's in, the only current production 6V6's strong enough to handle the voltage in an RM amp are JJ's. If they did indeed use TAD's and they are really 6V6's (not 6L6's), that's probably your issue right there.

 

[deedub]

They're TAD 6L6's. I replaced the chassis preamp tubes, and I'm still having the problem. I guess the next step is to pull the chassis and look for loose connections.

As a precaution, even though I've done it before, I'll swap the tubes out of the module itself. You never know, right?