Alpha 112R

[george]

I'm working on one of these and have a few question.

The board has several mods or maybe they were factory after thoughts. R137 and R108 have aluminum electrolytics caps in series - decoupling? Also what is the purpose of all the inverters on the input of the reverb pan?

Anyone have a picture of a chassis they can send?

I believe Loudthud had written a brief explaination about the differences between the beta and alpha preamp designs but I can't find it.

The amp has the original driver but the VC is rubbing - going to drop in one of these http://www.parts-express.com/pe/showdetl.cfm?partnumber=299-407

Link to schemo - attachments won't upload http://i284.photobucket.com/albums/ll33/bonosurf/Alpha12revB.gif

[SUNNBODY]

Do you have three speaker wires instead of two in yours?  If so is one some kind of ground perhaps?  I have three on my combo and, last time I opened up the grill to check out my speaker I noticed it had an extra speaker wire.  I only connected two and there is a little buzz.  I'll have to look at it again.  I don't really use this amp that much anymore because I've been doing the low watt thing lately.  I love all of Sunn amps ss and tube as well.

[george]

Okay it is fixed. I did a bit of a shotgun repair on this amp. Replaced all the ICs with sockets, all the NP capacitors, all the bias/drive BJTs and MJ15022/23 to replace the damaged output transistors. Also replaced the zeners in the +-15V supplies since they appeared to be generating/contributing to the noise problem. Quiet as a mouse pissing on cotton

Replaced speaker with one from PartsExpress - two terminals and no ground connected.