Yamaha G100 amp

[mjgrx]

So I have been searching for the correct schematic for this amp. I found some for G100-212 I. But this does not match my unit. My pre amp is part number LC-80261, and I can not find the schematic for this amp. Can any one help please.

[doctor]

So I have been searching for the correct schematic for this amp. I found some for G100-212 I. But this does not match my unit. My pre amp is part number LC-80261, and I can not find the schematic for this amp. Can any one help please.

There are many models of G100: G100 head, G100-112(I,II,III),
G100-115(I,II,III), G100-210(I,II,III) and G100-212(I,II,III).

If your amp is G100, here is the service manual:

[greekie]

IMHO these really are great amps!

[mjgrx]

Thank You!

This seems to be the exact manual for my amp. Maybe now I can fix it. This amp only is labeled G100. No other ID's except for the PC board part numbers. Any idea when this was made? I can't find any dates on the unit. Again thanks for the manual.

[JoeM]

.... Any idea when this was made? I can't find any dates on the unit....

I owned a the 50W version IIRC around 1976 or 1977.

[mjgrx]

Seems that my pre amp has a problem, and the manual from "doctor" looks like my amp. But as I work with the preamp I find it does not match the schematic in the manual. Can another version of the plan G100 exisit? I am trying to trace the schematic but it not that easy (at least for me). Any one have any ideas on this?

[J M Fahey]

Check Ampix, there you will find 2 or 3 schematics kindly posted by Enzo, one of them might be a closer match.
Anyway, what is the exact problem you are trying to fix?
There are many versions of that amp; some FET based, others OP AMP based.

[mjgrx]

Thanks for you suggestions I will get Ampix. My amp has no output from the Pre Amp, thats my problem. I think my power stage is OK. Just changed the first JFET that is connected to the input jacks now I have a signal to the next transistor, but I am getting lost without a schematic. Any ideas?

[mjgrx]

Ok it is fixed!! Had to shotgun the pre amp and change all transistors and 3 jfet's, because I could not find the actual schematic, seems like it was most likey one of the Jfet's. This amp seem quite good. I was wondering what the orginal speaker cabinet might have had for a configuration. Any one have any info on this?

[mjgrx]

Thanks for the help!

Thanks to all who helped with information!