Hum in VTL 125 mono block amps

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 .

Katylied ; Good idea , I have tried one amp at a time still the hum I will try a different cable later today. Mrtennis ; Thanks for the idea I will try both things later today a different amp not possible right now but may be able to try that later Thanks Marc

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