Background and Issue:
I purchased a used Quicksilver Line Stage preamp from Audiogon last year, it’s an older 6DJ8/6922 design. Everything is fine, it was using the tubes the fellow who sold it to me had in it (my fault for not getting new tubes). Sometime a month or so later the wife and I are watching TV listening through the stereo system and a sudden enormous low frequency bang erupts from the left channel and then that channel goes dead. I immediately turned off the amp and preamp and then powered everything back up and still left channel is dead. So I powered back down got some spare tubes put them in the preamp and it comes back to life (so I had a catastrophic tube failure)… except there is now a very strange low frequency hiss unlike any normal ambient tube preamp hiss, and it is not volume dependent. Again the hiss does not increase or decrease in amplitude when the volume control knob is adjusted. It is not tube related as I can swap tubes channel to channel and the problem stays put, and not change in any discernable way. So now the fun part. I have replaced 70% of the components in this god damn preamp (all told it’s actually an amazing preamp! It’s simple, sounds great and is designed to be serviced! Which is unheard of today, I have great respect for QuickSilver) with high quality same or better spec components (higher voltge/temp) and I still have the exact same damn issue!!!!! I am going out of my friggin mind!!!!! Also as stated earlier the hiss or distortion is very strange its kind of like coarse burlap being rubbed against coarse burlap. I have replaced all of the electrolytic caps with same value caps all Vishay or Nichon 105C (they were 85C) I replaced all of the diodes and rectifiers, even a small op amp and I have the exact same issue. There are a few more resistors to change out but damn! Also I have no schematic so sometimes I just have to pull components test the values verify the resistor bands vs the test and then order new ones and install them…it’s a lot of fun…(no its not!) If anyone can help me to isolate the issue, or has experience with a similar issue and could help me isolate the exact component(s) it would be greatly appreciated. Another clue, the noise/hiss is not present until the relays (tube warm up) kick in so I assume that it is in the high voltage side. PLEASE HELP, I am becoming manic.
Thanks
Jeff
