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old amp, GA 77

BrianGWN

Great 'Double White' North ~ Electronics Specialis
Joined
Jul 15, 2001
Messages
1,401
Can anybody point me to some info about some amp called a GA 77 ? I understand it is some older Gibson amp, part of the various GA xx models. A friend has come across one abandoned somewhere, it may still be in one piece. Thanks.
 

lespauljr

Les Paul Froum Member
Joined
Nov 12, 2001
Messages
324
Yes,
It's called the Vanguard. I beleive single P15N & 6L6's. About 25 watts. Nice amp but don't go too long for it.
 

Tim C.

Active member
Joined
Jul 15, 2001
Messages
6,484
As Les Paul Jr. said, it is a 6L6 based amp that utilizes a cathodyne phase inverter and a 12AU7 as the phase tube. The output tubes are cathode biased.

If you get the amp and it seems too clean, try changing the phase inverter tube to a 12AX7. That will spice it up considerably.

I hope we answered your question. :)

Tim C.
 

BrianGWN

Great 'Double White' North ~ Electronics Specialis
Joined
Jul 15, 2001
Messages
1,401
Thanks for the info. I found a couple of schematics on the net for a few variations of the GA77.
Today I had just a quick peek at the amp, in someone's car trunk. The person who has it noticed one tube socket had only the stub of the shattered remains of a tube and yanked that out. He said he powered it up and most of the tubes lit up, so it may be salvageable without a lot of trouble.
It will get set aside for now but hopefully we will be able to do some work on it sometime in the near future...
 
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