[wushuliu]

i was using 5751's i believe and amprex 6922's. 350b's as well. i think upgrading the rectifiers might make a huge improvement in the sound quality, but they were relatively difficult to get to because of the terminal strip and caps.  i dont think shelded wires will get rid of that extra background noise on this amp, but let me know if it does.

Just to follow up. Yes if the volume is cranked there is noise, but since there's so much gain (too much really) I rarely get it to a point where noise is noticeable unless I have my ears right by the speakers.

[sandbagger]

Just ran across this thread..... WOW

Glad your having fun with it

[Tulisan9k]

Hi,
I'm new to this forum, and do own an SP3.  Yes, there is that cathode to ground resistor which does not appear in the schematic.  One of them went bad and prevented me from adjusting the bias correctly.  Have since replaced all 4 of them but with a lower value: 22 ohms. Following ohms law, also reduced the bias voltage to 0.7 volts.  Did I do this right? 

BTW, best sounding tubes for me are the KT66s, although I had to get some socket extenders since the bases are too large to fit into the recessed octal sockets of the SP3.