Help with a Gibson GA-8

[lpf4]

Hey guys, so I picked up what looks to be a 62 Gibson GA-8 Discoverer off ebay, and am a bit lost on the tube complement. Everything I see online is saying it should be carrying 5 tubes:

GA-8 Discoverer: 6EU7, 6C4, 2-6BQ5, 6CA4 (correspond to Epiphone EA-35 Devon)

Just at first glance, this guy has has 4 tubes, and 2 of which are 6V6's... Which would correspond to the 61 Gibson GA-8, but that is a "Gibsonette".

GA-8 Gibsonette: 12AX7, 2-6V6, 5Y3

This is clearly a "Discoverer" as evidenced on the panel, and the 12" speaker. Does anybody know much about these? I'm a bit curious as to the schematic and tube complement I should be looking at to dig into this thing.

[Phil_S]

Start here to attempt a proper identification of the amp:
http://www.superiormusic.com/page199.htm
more than half the way down the page. Don't be fooled by the "other" Discoverer with the 10" speaker about 1/3 the way down the page.

This is what it says, these are the Crestline models:
GA-8 Discoverer: 6EU7, 6C4, 2-6BQ5, 6CA4 (correspond to Epiphone EA-35 Devon)
GA-8T Discoverer: 2-6EU7, 2-6BQ5, 6CA4 (correspond to Epiphone EA-35T Devon)

These are the earlier tweed models about 1/3 of the way down, with 10" speaker and 4 tubes:
GA-8 Gibsonette: 12AX7, 2-6V6, 5Y3
GA-8T Gibsonette/Discoverer: 12AX7, 2-6BM8, 5Y3

So, is it tweed or Crestline? I'm attaching a picture of my Scout, of Crestline vintage. It shows the crest, black elephant hide, and wheat colored grille cloth.

Got a picture to share? Either model, both are neat old amps with good tone. Not very loud, which can be a good thing!

[lpf4]

I definitely have a Tweed (will work on attaching a pic later from home), but it has a 12" for sure, and the 4 tube compliment that I had thought only the 10" model carried.

So, I also put a post on the gear page... and Walt Campbell hit me with this. Mysetery solved, and pretty cool bit of info on these old Gibsons as well.

"There's a great deal of confusion in Gibson's amp numbering and labeling over the years and you've jumped into one of the more confusing ones. Gibson's Master Service Manual lists *two* GA-8 Discoverer amps, one w/ 6V6s like yours and one w/ 6BQ5's like the Devon. It also lists a GA-8T Discoverer w/ 4 tubes that is completely different than the five Discoverer Trem. model amps (labeled GA-8T) that I've owned or worked on over the years. The latter are much more closely related to the 6BQ5 GA-8's than the amp listed in the service manual.

Looks like yours is one of the variant GA-8's from an earlier period.
__________________
Walt Campbell
Campbell Sound
http://www.campbellsound.com/"

[Phil_S]

I've known Walt via some amp forum somewhere, can't remember exactly where. I think he's a good guy and gives good information. Now that you own a Gibson amp, you'll appreciate the joke among those who have them. Gibson often made the "amp du jour" apparently with whatever was in stock that day, week, month, and frequently deviated from the schematics and designs without any surviving documentation. It is simply not surprising that you've got one that's a little bit different. There might even be transitional models between the tweed and crestline amps, where the cosmetics and the amps are mixed and matched! If you can believe the published production record, the tweeds were discontinued in 1961.

You can date yours by getting the date codes off the transformers, pots, and speaker, if it's original. Caps sometimes have a visible code, too. There should be a 6 digit number where the first 3 digits are the maker's EIA number (Clarostat, CTS, Woodward-Schumacher, etc.) the 4th digit is the year, and the last 2 digits are the week. Of course, you've got to get the decade from context - in your case 1950's to 1961. On occasion, these numbers are 7 digits where the maker's EIA is the first 3 digits, year is next 2 and week is the final 2.

I've got a transformer set from a mid '60's GA15-RVT that use the 7 digit code formatted like this: xxx-66xx, so the year is clearly 1966. Since we know the parts had to be in inventory before the amp was made, we generally assume the amp was made within a reasonable amount of time after the production date of the parts.

It would be nice to see a few pictures, including the insides.

Enjoy your new amp.

Phil

[Travst]

It could be a lot worse. You could have a GA-95 "Apollo"... like me.

[Phil_S]

John, Did you ever get the Apollo fixed or at least to satisfactory operation?

[Travst]

John, Did you ever get the Apollo fixed or at least to satisfactory operation?

It's much better, but there's still work to do. I set it aside to build a Telecaster for the TDPRI competition and a couple of other projects. I'll go back to probing it soon. I've been able to do some reading and studying on the topics that people brought up in my thread on the amp.

[lpf4]

Sorry about that Phil.. been a minute before I could get these posted...

[Cliff Schecht]

I'd probably change out that large wax paper cap for something more reliable. Wax caps+tube amp heat=trouble..

[Phil_S]

Ooooooooooh! Niiiiiiiiiiiiiiiiiiiiiiice! Yes, change that one cap before doing anything else. It is hard to believe. That amp looks nearly factory fresh.

[Scumback Speakers]

I've got three of these GA-8's, two Gibsonette's, one Discoverer. They all came with dual 6V6, 5Y3 rectifier and 12AX7 preamp tube. You can put a GZ34 rectifier tube in there to make it louder/stronger sounding.

The 12" speaker should be replaced with something beefier, I'd suggest an old G12H30 8 ohm model that's well broken in, or you could go with a Celestion Gold.

They break up pretty early, around 3-4 on the volume knob, but really saturate around 7-8, then they over compress after that like Neil Young's tone.

Lots of fun, let me tell you!

[dartanion]

I've got 2 Crestlines that are in primo shape, a GA-8T and a GA-19RVT. Both are very cool little amps.