The amps are less than a year old.
Contact your dealer first,if you get no satisfaction then contact the manufacturer.
Just a thought.
I picked up a matched quad of electro-harmonix KT88's from my dealer who sold me the amps. There not from Quicksilver but I had to make a choice, no music for the long Easter week-end or wait for Quicksilver tubes. The choice was clear.
I haven't had a chance to have proper listen and the tubes probably need to burn in a bit before I come to any conclusions. Based on my first impression, the sound is much different, drums and bass are more pronounced but with less warmth.
Thanks for the input.
I am not familiar with EH KT88s. They may need a little burn-in time to sound their best.
Quicksilver has been selling Chinese KT88s for years. They sound very good. In fact I was considering Gold Lion reissues for my Dynaco MKIIIs, but all recommendations were for Shuguang Chinese KT88s.
Let us know how it goes with the EH tubes.