Gibson GA20 schematic needed

[Burnedfingers]

Hi,

I am looking for a Gibson GA20 schematic. It has (3) 12ay7's, (2) 6V6's, and (1) 5y3 in it. Any help would be apprecited. I have looked on line but keep turning up GA20's with octal input and driver tubes in them.

 

[alejo]

look at this page:

http://www.drtube.com/guitamp.htm#Gibson

 

[Burnedfingers]

Thanks but they are incorrect. I need the schematic with the 9 pin tubes in the front end.

 

[alejo]

Ok. see this, but use 12ax7 in front

http://www.angelfire.com/mech/beansamps/schems/GA20.pdf

 

[Robert McLean]

Here is a third choice :
www.schematicheaven.com has a document called Gibson Amplifier Master Service book, file name Gibson_msm.pdf with tons of Gibson schematics in it.

For the GA20-T is shows 12AY7 inputs, ie nine pin tubes, so it may be what you want. The downside is that the schematic is not perfectly legible.

 

[Burnedfingers]

The schematic that Alejo posted looks correct. The other schematics have either incorrect number of tubes or types of tubes. I even emailed Gibson and they sent me the schematic with the octal front end in it. The 1956 Gibson looks like it is mostly correct. Was this amplifier produced by Weatherford amplifiers for Gibson?

 

[Burnedfingers]

Schematic of Gibson GA 20 as built.


I am only getting about 2 volts total output from this with a sine wave input.

Any ideas?