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First tube amp, it needs maintenance
First tube amp, it needs maintenance
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Old 22nd July 2010, 07:42 AM   #1
flyingsquirrelman is offline flyingsquirrelman  United States
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Default First tube amp, it needs maintenance


I have a 1965 Ampeg Model J-12, just the amp no box because it got destroyed

I have 4 out of 5 tubes, i know the tubes are old and used and your suppose to change them and i think these need some changing because iv seen this amp used for a decade. Problem is i don't know where to find these parts or how much they cost.

Types of tubes it already had in it


6SL7GT TUNG-SOL 3226508-3



GE 7591, these got allot of writing thats scratched off so i can't read the rest.

Any help would be awesome THANKS
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Old 22nd July 2010, 01:36 PM   #2
TheGimp is offline TheGimp  United States
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Location: Johnson City, TN
Since you have identified the output tubes as 7591s that limits which schematic applies. There are several variants up to a -J here but with no dates :

The Free Information Society - Audio Electronic Circuit Schematics

It could be a J-12A as it is the only variant with 6SL7s.

Your fifth tube should be a 5Y3 rectifier. This is a large tube with an octal (8 pin base with polarized center pin.

Your tubes would be:

6SL7 twin triode as input and Tremolo
6SL7 as phase splitter
two 7591 output tubes
5Y3 Rectifier

These can be found from a number of tube suppliers, or off auctions like ebay.

If you can find someone locally to you that has a tube tester, you may find some of your tubes are still good.

What are your plans for the amp? Occasional playing around the house? Get together with friends and play? Serious playing?

Last edited by TheGimp; 22nd July 2010 at 01:41 PM.
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Old 22nd July 2010, 06:25 PM   #3
flyingsquirrelman is offline flyingsquirrelman  United States
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Join Date: Jul 2010
Thanks for the reply

I just so happens that i forgot that i had the back board from the original box, i kept it because it was the only documentation. It's got a schematic on the back, well almost because allot of it is ripped off and nasty.

You were spot on...

The Model: J-12-A

Tube location (from left to right)

6SL7 6SL7 7591 7591 5Y3

I'm not sure what i'm going to do with this amp, it's a jazzy blues type amp and i haven't listened to it in a long time and the guy who used to play it was horrible. I became interested in it because i just found a fender bass but that needs work to.

When i get it working i will know if it works out but if anything it's going to be used for home use as iv always seen it used.

It's brand new, no corrosion and the chrome shines

Looking at the back board i have an idea of the box dimensions but have no idea how far out to make it.
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Old 23rd July 2010, 03:53 AM   #4
Enzo is offline Enzo  United States
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Join Date: Sep 2004
Location: Lansing, Michigan
The tubes may be worn, but chances are they are fine. Those 7591s are hard to find, but they were also a pretty robust tube, and yours may be OK. Real 7591s are rare, but I should point out, that a couple factories are now making "reissue" 7591s, which are close enough to being real. JJ and EH, that I know of, are making them.

They also used to sell a socket adaptor you plugged into a 7591 socket that allowed you to then plug a 6V6 into the adaptor. 6V6 being very common. Now that the reissues are out, I don;t see the adaptors any longer.

This amp is 45 years old, and if anything in it needs changing, it is probably most of the capacitors.

I good general resource for your tubes and tube guitar amp stuff is Antique Electronic Supply. They sell most tubes that are available, both new and new old stock. They sell all the capacitor types, they even sell handles and cabinet corners and grille cloth. Request their paper catalog and browse through it to learn what they offer.

Antique Electronic Supply

Another good resource for tube guitar amps is Schematic Heaven, a source of many schematics. Schematic Heaven - FREE Amp Schematics Tube Amp Schematics Valve Amp Schematics Effect Schematics Effect Pedal Schematics Guitar Amp Schematics Bass Amp Schematics Fender Amp Schematics Marshall Amp Schematics Gibson Amp Schematics Vox Amp Schematics
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