Ampeg GS-12 Rocket 2

[thewizardofaz]

Hi folks. I've got a GS-12 Rocket 2 and cannot find a schematic, can't pin down the serial number, it's just like it didn't exist. The ampeg book references in being built in 65 and maybe 66, but it kind of slips from one time line in 65 to being missing in the next timeline in 67. Serial is 018159. That does not seem to fit anything. I'm guessing it's a Gemini derivative, but it's just a guess. Tube compliment is supposed to be 2x7591, 7199, 12ax7. The previous owner put a 12AX7 in the 7199 socket. The original owner sales sticker in the cab says it was sold on 3/66. The OT numbers are 1514 and 682606. I can't see the PT numbers at all without removing the chassis. Speaker is a CTS 137 5812117. There's a long metal can on the chassis I'm assuming is the rectifier, with numbers 018159 10816606.
I'd really like to find a schematic and know why I cannot figure out the serial number
Thanks a lot
Rick

[dwhutchens]

Has it got reverb? I found a diagram for a reverb model. The can may be the filter caps. Did you find this site:

http://home.rochester.rr.com/piazza/

[thewizardofaz]

The Rocket 2

It's not the reverbo/reverberocket. Just plain old Rocket 2. I found one schematic, but it's totally whacked, with only one tube the same as the tube chart in mine. I did finally figure out the year though. What's also whacked is that someone modified it, had to, because there's a 12AX7 in the spot where there should be a 7199. I don't think it would run with the 12AX7 without being modified.

[dwhutchens]

It don't look like this does it?

[Enzo]

Or the tube chart never matched the amp in the first place. Sure wouldn;t be the first time that happened. You're lucky it isn;t a Gibson, those almost never match the schematics.

Look at the tube socket, the 12AX7 is a dual triode, the 7199 is a triode/pentode, they are not remotely equivalent. Meaning that it would not be a matter of just changing which pins the wires go to, the whole circuit and type of PI would have to change. There should be plenty of evidence these changes were made, if so.


Go to Schematic Heaven and look up the GS-15r. Now ignore the V5 and V6 circuits along the bottom - the reverb and trem - how does it compare to your amp? It has the 7199 PI, 7591s and a single 12ax7.


You say you found a schematic but it didn;t match your tube chart. But how well did that schematic match what was inside your amp?

[thewizardofaz]

Rocket Two

That picture you're showing is a late 50s Ampeg, if I'm not mistaken. Mine looks exactly like a 65 GS-12-R from '65, it just says Rocket 2 instead of Reverberocket 2.

The tube chart inside matches all but that one tube - the 7199/12AX7 as far as what's actually in it. The schematic I found had 2x 6SL7 and 2x 7591A listed. Way off. I'm not savvy enough to tell what's been done, if anything. I'm gonna have a friend take a look at it. He builds and fixes, but lives up north in Phoenix. I should see him in a couple of weeks.

[Enzo]

So did you look at the GS-15r suggestion I offered?

[thewizardofaz]

rocket 2

I'm schematic challenged. I wouldn't be able to tell really. I'll have to get my friend to check it out when he comes down.

Thanks Enzo.

[thewizardofaz]

more stuff.

Hey Enzo, I don't think I mentioned that this amp has the original sales sticker inside the cab, stuck to the cab wall. It was originally sold to a Mr. Doty in Lincoln Park, Michigan. Neat.

[thewizardofaz]

Rocket 2

It occurred to me that the schematic I was looking for might be on the back of the back panel of the Ampeg, and it was. And guess what? The tube chart I was talking about that's on the inside of the cab doesn't match the schematic. Instead of the whacked out hard to find 7199 tube, the schematic shows 12AX7 for both preamp positions. One of the 12AX7s is split. I'm happy now. Whew

Rick

[Bmxbarspin724]

I have that same exact amp, and I'm pretty much positive that mine was not altered. it uses one 12AX7 and one 7199. and for the output section it uses two 7591s. If that's the conclusion you came too. great. i just didnt know.

[KingCameron]

I've got this one!

Yo Wizard,
I can help you here...I have researched this as well.

I also have a GS-12R on the bench. In my case, ...there are two schematics that have the tube configuration of my amp (different PS caps, different circuit)...I have had to be very careful in finding the right schematic for my specific variation of the Amp.

There are several versions of the GS-12R ("G" for Gemini)
7591 7591 12AX7 6U10 12AX7 (my version)
7591 7591 12AX7 12AX7 6U10
7591 7591 12AX7 7199 6U10 (your version)

The 7199 is considerably different from the 12AX7, in that is a pentode and a triode in one bottle. (the 12AX7 is a dual-triode)

I beleive I have attached the right schematic for your version, please confirm.

Please send pictures of your circuit. I am interested to see how it varried from my amp.

[RWood]

I have that same exact amp, and I'm pretty much positive that mine was not altered. it uses one 12AX7 and one 7199. and for the output section it uses two 7591s. If that's the conclusion you came too. great. i just didnt know.

I have this same tube lineup in my Gemini IV. It has tremolo but no reverb. It uses:
12AX7
7199
7591
7591

Solid state rectifier with the PT110V power transformer. Original CTS speaker, dates from 1964.

I have searched but have never found a schematic for this one. Close, but not exact. The schematic that had been pasted inside the cabinet was removed by the time I got the amp in 1983. The tube chart is for a G-12 and has four tubes (6SL7s and 6SN7s) scratched out and 12AX7 written in it's place. The serial number sticker designates it as a GS-12.

I have never seen or heard of another Gemini IV.

BMX, is yours a Rocket or a Gemini?

RWood

[Enzo]

Hi RWood, welcome to the forum.

You will find, as have many many others, that Gibson models and Gibson schematics often do not coincide. Changes over the life of a model name were often not documented, and the innards could change completely at any time. And yes, what was once one model can become the insides of a different model. Not only that, since the Epiphone amps were made in the same factories, many times the missing link Gibson schematic can be found as an Epiphone model, and vice versa.

When I have a mystery, I get out the Gibson master book and leaf page by page looking for tube complement. Once in a while we get lucky and it is what it says it is. But I have one model - I forget now which without opening the book, something around GA15 to GA19 - for which I have three published schematics plus THREE MORE of my hand drawn ones. All different, and all for the same model name. That is six different drawings for one model.

You may never find a schematic that matches your amp. Parts of it might match several models even if none matches the whole thing. Good luck.

[RWood]

Yes, I just went through that with a Gibson GA-45RVT (not a Saturn.)

I've realized over time that having that actual amp is better than having the schematic, as long as someone hasn't modified it too much in the past.

Just tonight I [finally] fixed the tremolo on that Ampeg - it has never worked since I bought the amp over twenty five years ago. Turns out the cathode wasn't grounded on the trem tube's triode. I am flying high right now!

Sorry for the hijack. Now to cool the bias down from 94mA............