I have recently been given a full Audio Research setup consisting of in various non-working order an SP-3 preamp, a couple of d'76's and an ec-3, a couple of fan bases for the power amps and matching stands.
Now here's the thing I'm not really into valves, usually strictly a solid state guy, vintage of course but these have peaked my interest and I want to restore these piece buy piece, so here's hopefully where you guys can help me with ideas, parts etc.
So I have started with the Sp-3, here's a link to the schematic, http://www.audioresearch.com/Content...rts List.pdf
http://www.audioresearch.com/Content...20Cap PS.pdf
There was a few shorted capacitors in the power supply, so I've decided to replace all with new, I also don't want to go down the restuffing route I just don't think it will go well. I've trawled mouser trying to find some of the same series for all the capacitors and have hopefully settled on Panasonic FM (2200uf 50v) for the 1500uf 50v ones (c29/30) and Kemet alc10 (330uf 450v) for the 300uf 300v ones (c43/44) the dual 75uf 475v (c45/46) ones I could either go 100uf 500v kemet if I can find them or 80uf 550v which i can find these will be mounted top and tail, data sheet for Kemet here, Mouser Electronics - Electronic Components Distributor
Other thing to replace, should I bother with new resistors if I'm going for high reliability? I've already replaced the diodes on the power supply pcb as this was cheap and easy.
Feel free to chip in, the more the merrier.
Kind Regards
Chris
Now here's the thing I'm not really into valves, usually strictly a solid state guy, vintage of course but these have peaked my interest and I want to restore these piece buy piece, so here's hopefully where you guys can help me with ideas, parts etc.
So I have started with the Sp-3, here's a link to the schematic, http://www.audioresearch.com/Content...rts List.pdf
http://www.audioresearch.com/Content...20Cap PS.pdf
There was a few shorted capacitors in the power supply, so I've decided to replace all with new, I also don't want to go down the restuffing route I just don't think it will go well. I've trawled mouser trying to find some of the same series for all the capacitors and have hopefully settled on Panasonic FM (2200uf 50v) for the 1500uf 50v ones (c29/30) and Kemet alc10 (330uf 450v) for the 300uf 300v ones (c43/44) the dual 75uf 475v (c45/46) ones I could either go 100uf 500v kemet if I can find them or 80uf 550v which i can find these will be mounted top and tail, data sheet for Kemet here, Mouser Electronics - Electronic Components Distributor
Other thing to replace, should I bother with new resistors if I'm going for high reliability? I've already replaced the diodes on the power supply pcb as this was cheap and easy.
Feel free to chip in, the more the merrier.
Kind Regards
Chris
Member
Joined 2009
Paid Member
Sounds like a rewarding project - sorry I have no experience to contribute here but glad you are sharing it. Some photos ?
All the Dale resistors should be fine. Check any other types for drift.
Bring each unit up slowly on a Variac if possible.
Be sure to set the amp bias to a low value, and the DC balance centered, to start.
The amp's AC balance can be at center to start, and only is changed if you have distortion measuring gear.
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I've gone ahead and redone the Psu on the SP-3 here's a pic waiting to be reinstalled
An externally hosted image should be here but it was not working when we last tested it.
Be sure to clean off and renew the thermal grease on the regulator transistor/heat sink assembly.
A new volume control, especially a switched resistor attenuator, would be a good idea.
If you use the phono inputs, wire the jacks directly to the board instead of through the phono 1/2 switch.
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I had to repair an SP3 a few years ago, filter capacitors were shot (not shorted, but not doing any filtering). Original parts weren't available, even from Audio Research. They had a replacement part, but it had to use an adaptor kludge plate to mount it. They also wanted pretty much $$ for the replacement part.
I took the original caps and hollowed them out (not fun, and made a real mess in the workshop). Put Panasonic caps inside the original shells, fortunately modern caps of higher voltage and temperature ratings still fit easily in the old huge cap shells. Not sure it was worth all the work, but it worked fine, and preserved the original appearance (not sure if the owner actually cares, though).
I took the original caps and hollowed them out (not fun, and made a real mess in the workshop). Put Panasonic caps inside the original shells, fortunately modern caps of higher voltage and temperature ratings still fit easily in the old huge cap shells. Not sure it was worth all the work, but it worked fine, and preserved the original appearance (not sure if the owner actually cares, though).
I have an SP-11 with a completely re-rigged power supply. I think the original transformer was improperly spec'd
A couple of resistors have drifted out of value on this amp, what's the consensus on replacements, i.e brand/type?
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