Gibson GA20 schematic needed

Original Burnedfingers · 1st December 2006, 10:57 AM

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 · 1st December 2006, 11:17 AM

look at this page:

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

Original Burnedfingers · 1st December 2006, 11:38 AM

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

alejo · 1st December 2006, 12:00 PM

Ok. see this, but use 12ax7 in front

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

Robert McLean · 1st December 2006, 03:39 PM

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.

Original Burnedfingers · 2nd December 2006, 10:20 AM

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?

Original Burnedfingers · 3rd December 2006, 10:30 AM

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?

1st December 2006, 10:57 AM	#1
Original Burnedfingers diyAudio Member Join Date: Nov 2002	Gibson GA20 schematic needed 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.

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1st December 2006, 11:17 AM	#2
alejo diyAudio Member Join Date: Jun 2004 Location: bs.as.	look at this page: http://www.drtube.com/guitamp.htm#Gibson

1st December 2006, 11:38 AM	#3
Original Burnedfingers diyAudio Member Join Date: Nov 2002	Thanks but they are incorrect. I need the schematic with the 9 pin tubes in the front end.

1st December 2006, 12:00 PM	#4
alejo diyAudio Member Join Date: Jun 2004 Location: bs.as.	Ok. see this, but use 12ax7 in front http://www.angelfire.com/mech/beansamps/schems/GA20.pdf

2nd December 2006, 10:20 AM	#6
Original Burnedfingers diyAudio Member Join Date: Nov 2002	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?