When you say B100, do you mean a G100 212 ??

like this?


If so search for G100 as from what I've read in the past, these amps were only listed as "B" in Japan, rest of the world knows them as G. You can find service manuals for them online plus the Yamaha site has the owners manual for the Series III version (final version of the model run)
One pictured is a Series II, I bought it a few weeks ago off ebay UK and it came with the mutilated Duo Sonic.

Killer deal as these amps are fantastic and always go under the radar. I need to refurb it a bit, there is a split in the handle and the EQ pots are scratchy, but I'm holdign out on taking it aprt just yet as I've only just got it.

I have Yamaha G-100 ll thats in a 2-12 cab that looks like a Fender super reverb. I'm always being asked what kind of tubes I use to get that great great tone. I just reply "Thanks"