Tube for Tremelo on Gibson amp?

G

Gdntoneguitars

New member
Any recomendations or preferences on what would be a good tube replacement for the tremelo in specific on a Gibson GA-20RVT?

Just got it the other day, 2 channels, Reverb & Tremelo footswitchable on one of 'em, but when the trem kicks in, the volume dips down a bit, and the trem effect itself isn't very noticable at all.

I can deal with a subtle trem effect, it's kind of nice and not over the top, but I attributed the volume drop to that tube possibly being on its' way out. The reverb however, I really like. Makes it nice and spacey.
 
Re: Tube for Tremelo on Gibson amp?

There are actually 2 tubes in the trem circuit of your amp: V3 controls the frequency and is also the reverb recovery amp. V5 controls depth and doubles as the phase inverter. There is an internal adjustment (500 ohm pot) that biases the effect so that when it is turned on the level is the same as when its off. If you aren't comfortable inside an amp, take it to a reputable tech.

Tube replacement won't do much: V3 is a 6EU7, NOS is probably your only choice. And V5 is a 12AU7, low gain so replacing it won't buy you much unless you switch types which will make it necessary to change circuit values...in fact, check and make sure this is a 12AU7 in your amp; a 12AX7 in this position could cause the problem you describe.

Jerry
 
Re: Tube for Tremelo on Gibson amp?

I opened it up, and it looks like there are 5-12ax7's and 2-6V6's in there.

I looked online and I couldn't find much to tell me what's supposed to be in there.

When looking at the back, is V1 the leftmost position?

I'll see if I can find any 12AU7's at the local shops to try to swap them out if that's the case though.

Is there any chance of damage if 12ax7's have been installed rather than 12au7's?

-Thanks
 
Re: Tube for Tremelo on Gibson amp?

How old is your GA-20RVT? My recommendations were based on the older ones that would have had 6BQ5s for output tubes. If yours is a newer one, disregard my info...

Jerry
 
Re: Tube for Tremelo on Gibson amp?

Ha! I did find some info, and the Gibson site does say it's supposed to have 12ax7's.

It is a newer one, though also discontinued. Still worth cracking open to see if there's a pot to adjust, or would that be only on the old circuitry?

I may just get a new set of tubes and see what that does.
 
Re: Tube for Tremelo on Gibson amp?

I'm thinking it won't have the adjustment pot in it. I have the Epiphone equivelent from the early 70's and it doesn't even have that pot. Swap around the 12Ax7s that you have and see if characteristics change, if so, then buy a new tube or two.

Jerry
 
Re: Tube for Tremelo on Gibson amp?

Unfortunately, a volume drop with trem engaged is not that unusual and was kinda common in the old Gibson amps...although a tube swap to something with a little more oomph may help. Good luck...
 
Re: Tube for Tremelo on Gibson amp?

I'm off to buy a couple new tubes tomorrow (I only had EL84's left), so I'd like to have a few on hand anyway. I'll report back with any changes/improvements.

I have to say though, that this amp is awesome. It's the first amp that I can dime out and not kill myself with. I'm a big fan of the cleans (I've heard better, but not for the $500 I spent on this amp). It breaks up nicely, but not in an overdriven metal kind of way.

Great little blues amp. And to think, just a couple months ago I was playing 5150's, and a Mesa Stiletto Trident. Night and day, but this is gonna be my sole rig for a while.

-Thanks for the help thus far.
 
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