KT88 Tubes

Apos - yeah no, not for me either. I use NOS 6550 by GE, RCA or Winged C in my KT88/6550 amps. Have had nothing but good luck with them. Best new issue are Good Lion KT88s but I'll spend more for the NOS mentioned. Just my experience & opinion 

I am new to tubes but not troubleshooting electronics.  Occasionally in my career I have used the swap method on some similar adjacent instrument only to kill that one also as the component itself was the issue.  Is that a possibility with a bad tube in this application?

@bgross , +1, I love Winged C’s, the only tube I enjoy more are GEC NOS. But it’s today and prices are crazy. I think the new GL’s are pretty good. I seem to go between the GL’s and Tung Sol KT-120’s. I recently had Rogue build my M-180’s into the Dark version and all new tubes. I hit about $4k with shipping both ways. What was interesting is they only offered Psvane KT-88’s based on current market reliability issues. I paid $475 for an octet with the plan of going to something better after burn in and setup. But the Psvanes are surprisingly good. I’m looking at new speakers and might need to go KT-120’s for bass depending on what I get. To the OP I’d really consider having your amp inspected and brought up to spec in addition to considering new tubes. My Rogue lost a single resistor in one of the input/phase circuits thus affecting the amp. However I sent both in for a checkup and was told that both had tired bridge rectifiers which effects SQ and would have ultimately failed. That’s a nice amp , fix it feed it , cherish it, play it every day. Cheers , Mike. 

@russbargmann before you insert mew tubes you may want to make sure you do not have a coupling cap leaking DC or a loose pin on a tube socket. These are two of the more common issues for power tubes red plating. 

Everyone, thank you for all the helpful suggestions. Over the net several days I will be trying them out.