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[Aal3474]

I am searching for a schematic for a Yamaha G100 head, serial #2167. I can find plenty for combo amps, but not this one. Any help will be appreciated.

[J M Fahey]

Heads and combo chassis are basically the same, except the speaker jacks and some other minor details.
The main difference lies in the production years.
Is it a G 100 I , II , or III?
What problem are you trying to solve?

[Aal3474]

I think it's good that I can say there are no problems detected with this amp head. I just would like a schematic for future reference should I need it. Not real sure whether it's a I, II, or a III since I find no designation anywhere on the unit. I will do some more research tomorrow and maybe even post a pic here.

[J M Fahey]

There's a lot of discussions about them, just use google.
Cosmetics are very different and help ID them.

[Aal3474]

http://music-electronics-forum.com/attachments/11058d1285307419-g100-service-manual.pdf.
I think this is the correct schematic for this amp. Unfortunately, I still have not determined whether it's a I, II, or III. The case matches exactly and I have seen several that are completely different from what I have.
OK. I have determined this IS a I head. The II has a different cloth on the front, and the III has what appears to be stamped medal. I also found one with a ser.# in the 1700's, made in '79. Mine is numbered in the 2100's.

[J M Fahey]

Cool, post a couple pictures of yours.
Excellent amp, but always be sure to use good speaker cables and proper cabinets.
Although it has short circuit protection, they are never 100% effective, and repairing that amp may be a nightmare so be doubly careful.

[Aal3474]

I have tested this amp thru a Randall 4x12 cab a friend has and it just great. I have plans to use a couple of Celestions I have that are not busy right now for a 2x12 to run it with. Since I have no use for a half stack, I can get by with the 2x12 and not run at full blast. Yet, another project for the warden (wife) to complain about. Here is a couple pics:

[J M Fahey]

Thanks for posting.
Cool amp, very loud and clean.
It's a "I" , although usually the "1" of anything does not get a number , they get one when there's a new version and people want to distinguish between them.
If your 2x12" has 2 good 75/80W speakers (or better) you can use them without fear.
The original combo used 2x12" speakers.

[Davelectro]

Series I= discrete (JFET/BJT) preamp circuitry.
Series II, III= op amp-based.

Hope it helps!