Puggie

Well, I'm in contact with the UK distributor, to be honest I wouldn't give my amps to the UK authorised repairer, for a number of reasons. This industry is VERY paranoid, in pro audio schematics or service manuals are readily available for anyone to purchase, it seems crazy, I used to not buy any product I couldn't get all the servicing info on myself out of principle. We will see what happends, If for any reason they cannot supply me with schematics or a service manual they will go to the authorised repairer be fixed and sold. and I'll move on to someting from a more helpful manufacturer.

Is there any way I can get schematics for an old USA 2000X, USA1000 and USA-150? they all need repairs and being the other side of the pond in blighty I'd rather repair them myself. The USA 150 has smoked some FETs and PSU diodes. The USA 1000 cuts out intermittantly (could just be a dry joint) both those have been abused a bit in the past (not by me, I'm trying to bring them back to their former glory and give them a good home) The USA 2000X was reverse polaritied by a moron (along with the rest of my car when he tried to jump start it) and now has PSU/system noise appearing on the audio, probably jsut a diode gone somewhere but schematic would make it somewhat easier to find. any way I can get help with these, I just need schematics so as I don;t have to reverse engineer the whole damn amp to rind the faults. P.s. the 2000X rocks when its working, its used for powering my whole system in trimode.

Well, they have been in for over a month now and still sounding great. they seem up to the job.

I want to fit better quality tubes to a TU-600, do I need to re-set the bias/plate voltages or are the pre-amp tubes auto-biasing? if so where to I tweek the levels and where to I measure. thanks.

Still no response I changed the tubes anyway. Its now running a pair of JJ Tesla ECC83s tubes and sounding much the better for it tonality and staging are a definitel improvement of the Sovtek 12AX7LPs fitted as standard. I'd still be interested to know if I can set the plate voltage / bias by the variable resistors on the board for this amp.

Anyone, surely someone must know if I can just swap the tubes and go or do I need to tweek and voltages?