Posted by bernieclub [ 205.188.116.67 ] on April 05, 2005 at 21:47:28:
In Reply to: Got it, posted by Wayne Parham on April 05, 2005 at 18:56:19:
Wayne,
First I want to thank you for your willingness to jump into my problem with both feet. I'm hoping that the glitches will be minor, and the upgrades effective.
Per my email, my main concerns are a bad selector switch, (Frank has emailed to let me know he's still trying to contact Nelson Audio), and the missing capacitors bypassing the resistors in NFB loop. I've double checked the underside, and it is a 220K ohm that goes from the 8 ohm OPT tap to the cathode of the 12au7. The cathode resistor is 1K ohm. I can see the caps in the picture of the underside of the amp on FSAudio website!!...small films with clear dielectric. I gather the caps are necessary to add NFB to counter the rising response as frequency increases of the pentode kt66s. (amazing the tidbits I'm picking up...I'll be dangerous soon) Anyway, I've learned that it's not possible to calculate the cap value without knowing all the other parameters, and possibly having some serious testing equipment. On to upgrades... the issues I'm having are:
with my 96db speakers, there is noticable hum and hiss. I think there is room for some HV snubbers, and heater snubbers. I'm sure a choke in the B+ would work wonders on the bass, but I can't quite figure out where to put it. If I really knew what I was doing, I'd modify for triode operation, but I'd need explicite direction. Since there doesn't seem to be a schematic available, would it be worth my time to map one out myself? Would it benefit this community if it were posted? Would I get into trouble for it?
Thanks for reading this tome!
Bernie
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