Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Hello all.  I recently picked up an older JC 120.  I wasn't really in the market, but the guy was pretty much giving it away.  It is not without its quirks though.  The effects don't work, and it has been fairly heavily modified.  There are two extra inputs added to the back along with a toggle switch and two XLR jacks.  There are also three relays that don't look stock, but I'm not sure about those. He also added a small board with a chip on it.  He may have been trying to add delay, but it's hard to be sure.

The amp came with a binder full of notes and graphs, hand drawn schematics but unfortunately it doesn't have the original schematic.  The amp I have is an early model, I believe in approximately 1978-1979 or so.  It is one without the bright switch or the distortion footswitch.  I haven't had any luck finding that particular model.  I'd like to start putting this thing back to something approaching stock.

If anyone can help I'd appreciate it.  Also a drawing that shows component layout would help me.  It looks like he hasn't messed with the boards too much.

Try this:

This looks perfect.  Thanks!