Mk III - missing dirt on Rhythm 2

[camsna]

So. Here's the thing. I SURE hope it's not an LDR problem. But I got my amp. Old tubes. The original owner says he hasn't played it since the 80s.

I plug it in. All seems fine. Except there's NO dirt or hair on R2. Volume? Sure. Breakup - not unless Volume is past 8 and Master is at 10.

Lead channel SEEMS fine. I THINK it's okay. There's a bunch of dirt there. Not as much saturation as I was expecting - but beautiful nonetheless.

I'm off to check the tubes now. I'm praying that's all it is! But - if it's not - will an LDR give itself away when it fails?

 

[MrMarkIII]

If the amp hasn't been played in 20 years, the problem may not be tubes. Tubes generally wear out from too much play, not too little. The electrolytic capacitors DO wear out from not being used regularly. As far as I know, LDRs either work or not. The manual has much info on what tube does what and how best to trouble-shoot them.

 

[camsna]

Yeah. I started yanking tubes, one-at-a-time. It SEEMS to be a tube issue. Truth is - I don't know how much he played on these tubes before he put the amp on the shelf. But. It seems, at this point, to be tubes. I pulled them and put a known good tube in positions 2 and 5 and I get a much more crunchy thing happening on both R1 and R2. So. We'll see what happens when I get my whole set of tubes in. Hopefully that'll do it.

I just wish I knew how much crunch I SHOULD expect from R2 as a point of reference! But I'll have to do what I can do with what I got now.

Thanks!

 

[MrMarkIII]

The crunch from R2 should be greater than R1 (even with Volume dimed), but always less than Lead. It's the "in-between" sound.

 

[phyrexia]

Have you replaced V2 with a known good 12AX7?

Oh I'm sorry, I see you've done so.

 

[camsna]

No luck. Replaced all the preamp tubes with known good ones - still there.

V2 doesn't hardly glow. Not like the other preamp tubes. And with Volume and Master dimed I get that sort of Ch 1 Marshall cranked all the way up kind of distortion. But no thick palm mutes. No 'chunk chukka chunk.' Just loud and a little bit hairy. But not mean 'n' dirty!

Am I expecting something I shouldn't? Even the owner's manual says that R2 is for 'metal' and has metal-ish setting suggestions. But what I'm hearing doesn't even approach Angus Young kind of gain!

AAAAAHHHHH!

 

[MrMarkIII]

"... Volume and Master dimed I get that sort of Ch 1 Marshall cranked all the way up kind of distortion."

That's R2: "Channel 1 Marshall cranked", etc.

 

[mrd]

Take it to a tech and get him to check the caps man... if that amp has been sitting around since the 80's then it's probably due for an all-around check up.

 

[camsna]

Ahhhh. It's like that feeling when you take an hour overdue leak.

All new tubes. Such beautiful tone. Dirt is back! Ch. 2 is different than I expected. But it's all so good. All new tubes affected my total output volume, gain, dirt - everything! The old'n's must've been very very dead!

Thanks for all the help. Now I gotta spend a month dialing it in!

 

[Buddy]

Good deal ! You are going to have fun with that bad boy ...

As Mr's " D " & "MarkIII" said , an amp that has not been exorsized (pun intended) in a long time may have cap issues . They usually show themselves with humming and loss of clean headroom , pops etc . Funny smells .... And they usually go at a gig , when you stretch out it's legs .

It would be a good thing to have a Mesa auth. tech to give it the once over.
Or at least open it up yourself and check the cans for bulges , leakyness , melted shrink labels.... . Carefully . Big voltage inside .

'Twould be tragic , messy , and expensive should one go .
And they usually take out some nearby components at least .

Have fun !