6550C vs KT88

Thank you all for your feedback.
Last night, I replaced the 6550 with my new quad matched KT88 in my Vt100 MKII. I was using PS Audio P600 power generator as the power source. As soon the VT100 is switched on, I saw the wattage meter on P600 keep going up pass 400 watts. Normally it should settle around 350 watts. Before I had a chance to check for bias, one of the resistor on the left channel closed to location V2 just broke off (the insulation part only). The smell was pretty bad. I have no idea what just happened, only the left channel (both right and left are biased very closely) had this problem. Is it my new KT88?? or just a bad resistor which could not handle the higher voltage??

So sorry to hear this. I know quite a few people, myself included, who run them without any problems. In fact a sales manager at ARC told me they had considered putting svetlana kt88's in as oem equipment.

Did you turn down the bias setting for the new tubes? As your old tubes aged, you would have been turning this up. I know the tubes have to be very closesly matched too.

From what I have read, usually these amps are designed to blow up a resistor when in trouble. You should be able to get it repaired without any permanent damage. I would give Leonard at Audio Research a call and ask him what to do. He's very helpful and will even ship you parts if you want to have a repair done locally. If you can get a local tube guru to do the work (and a checkup), it shouldn't be too expensive.

Good luck with the repair.
John.

I used Chinese KT88's for years in my D250MKII with no problems. Only had one tube ever fail!
GTF

Thank you John, I took my unit back to the local dealer, they had talked to ARC as well, KT88 is ok to used in VT100 MKII, not MKIII. Instead of replacing the resistor myself, I trust ARC more in their QA and listening test. I decided to go with MKIII update, hope I had made the right choice. BTW, I'm testing my quad matched Svetlana KT88 in a friend's tube tester, just want to make sure they are OK, since my new MKIII can't use them, I would like to sell them (less than 5 minutes used). Let me know if anyone is interested. Thanks again

HOW MUCH WOULD YOU LIKE TO SELL THE TWO QUAD KT88 FOR? THANKS! FREDDY