Gibson GA-20 restoration

[philo43]

I have a Gibson GA-20 chassis that came into the shop in a home-made cabinet with a Realistic 15" Hi Fi woofer. I'm not sure of the year but I should have no problem getting it in working order. I would like to rstore it to something near original. Can anyone point me to info and pictures of classic Gibson amps so I can build a cabinet that is at least partly authentic. I'm having trouble sorting through all the variations of Gibson amps through the years. Maybe someone can help with dimensions, speakers, coverings, etc.

[Phil_S]

According to the link, the GA-20 was made between 1950-1954. About 5,000 were made.
http://www.superiormusic.com/page199.htm
Some pictures:
http://online.physics.uiuc.edu/courses/ ... n_GA20.jpg
http://online.physics.uiuc.edu/courses/ ... n_GA20.jpg
A really good resource:
http://online.physics.uiuc.edu/courses/ ... _amps.html
http://hem.passagen.se/ekabjan/GibsonAmps.htm
Schematic:
http://www.webphix.com/schematic%20heav ... s/ga20.pdf

How's that? I this case Google isn't really your friend. It helps a great deal to know where to look.

[philo43]

Thanks, this has helped!

[Phil_S]

I suppose you'll have to guess at cabinet dimensions, although you have the chassis and you can get a relative sense of proportion from having the chassis and the pictures. I'd also guess standard pine boards haven't changed, so that cab is either 1x12 or 1x10 lumber. As for the joinery? As long as it's covered by some tolex, doesn't really matter.

You can see the 12" speaker outline. It suggests the width is around 22-24".

Good luck.

[philo43]

I estimated the handle to be about 7" long and that it takes up approximately a third of the width of the amp making it around 21"to 22". I build 1x12 combos at 23" wide so I'll probably just follow that. Like I said, I just want to come up with something that suggests the look and size of the original...not a perfect knock-off. I'll probably load it with a Weber 12" alnico. Thanks again!

[Travst]

Post pics of your progress. We can't have too many Gibson amp threads!

Phil, I'm still working on the GA-95. I slowed down to get a guitar build done for the TDPRI competition.

[EFK]

I've got a GA20 and can give you any dimensions you want, if you'd like. They are lightly-built, cab lumber is only @ 3/8" or 7/16" thick.

[EFK]

I've got a GA20 and can give you any dimensions you want, if you'd like. They are lightly-built, cab lumber is only @ 3/8" or 7/16" thick.

[philo43]

Thats interesting. Can you post a pic?

[loctal]

Yes please. I would love to know the dims. I have been looking for them on the web.

[philo43]

Hey Loctal, is that Stumptown, WV?

[loctal]

stumptown portland OR. I love their coffee.

I live in Vancouver WA. Some call it Vantucky, others call it "the Couve".

[pdf64]

According to the link, the GA-20 was made between 1950-1954. About 5,000 were made.
http://www.superiormusic.com/page199.htm

Check further down the page, GA-20 carried on till 1961, in 2 tone styling. Pete.

[Phil_S]

Yes, but the 2-tone later model was not the same circuit. Alas, the wonderful 6SJ7's were gone. I'm sure the later one was wonderful in its own kind of way, but certainly more ordinary 12AX7's into 6V6's.

[philo43]

Yes, but the 2-tone later model was not the same circuit. Alas, the wonderful 6SJ7's were gone. I'm sure the later one was wonderful in its own kind of way, but certainly more ordinary 12AX7's into 6V6's.

Yeah, mine is the later version. I'll rebuild the cab with 3/4" pine and tu-tone tolex, although the original was probably tweed, I think. I have the original hinged handle and the raised letter nameplate.

Too bad the Gibson amps had such flimsy cabinets. I have a late 50's Silvertone amp constructed of pressed cardboard-like material! Sounds good, though.