I’ll bet minorl is right. The KT150 is much more demanding of transformers than is the KT120. Verify that the tech is replacing the one in your amp with one rated for the KT150, otherwise you may end up right back where you are. Maybe consider getting the complete SE upgrade?
ARC REF 150 Buzzing noise
I have an ARC REF 150 amp with over 4000 hours on it, and recently it has developed a buzzing noise. This appears after about 30 minutes of use, and seems to get steadily louder. I thought it might be a tube. I had KT150 power tubes in it and I swapped those out for KT120's and re-biased. No change. I then swapped out the 6H30 input tubes and re-biased again. Buzzing is still there. It is very difficult to locate the sound on the boards. I have also had several blown fuses, this has been in the midst of a move and may or may not be reIated to the buzzing. I have to assume this needs a repair, but I am wondering if anyone has a guess or even better, experience with the problem. I am in the Denver area and if anyone knows of a local repair opportunity, I would appreciate knowing that too. I do not look forward to the expense and delay of sending it back to ARC repair. Thanks. Scott