Could be you are getting some low level hum from the small tubes? I've had that problem recently and solved it with new/different small tubes.
9 responses Add your response
I have now tried 4 different set's of tubes - Brimar , Telefunken , Mullard and Ram all 12AT7's no difference in the hum -noise level. I am at a loss as to why a hum- buzz has started happening as I never had it before and nothing else has changed in the system. I do not have a new set of output tubes but have several sets of lightly used EL34's and will try that and see if that makes a difference right now I use KT77's and I really like the sound from them they are JJ KT77's .
Couple of other things to try...
1) Disconnect the amp from the pre-amp, muting may not be enuf.
2) Makes sure that all unused PC's are disconnected from outlets (believe it or not another hum I had was sorced to exactly that!).
3) If that fails, bite the bullet and disconnect and unplug everything and start from scratch. One amp to one speaker, then the other, then both together, then add back....Sooner or later you will hear the hum and you will know the source.
Hope that helps a bit.
Vegasears ; Last year I had been told that a KT77 was a replacement that would work and it does and I think it sounds very nice. You are right the VTL amps are designed for a EL34 or 6CA7 tube. The KT77 may be pushed a bit in the VTL amps as I was told today by a designer of very high end triode amps. They can work just great but some minor circuit changes may be needed to get the most from a KT77. I have determined that the noise in the amps is in the input stage of the amps the output stage is very quiet . I now need to figure out what to do and how to fix the problem . I will be talking with Larry Moore of Ultra Fi the previous mentioned designer about how to proceed with a fix . I may also look in to getting the amps to work there best with a KT77 tube. Thanks for the ideas everybody this is what makes Audiogon great. Marc