Just curious. I have a Prima Luna Dialog Premium HP integrated. I replaced the stock Chinese EL34s with some JJ KT88s… these were well broken in… I had them from an old pair of VTL monoblocks I sold… 6 weeks ago, I installed 8 KT150s from Kevin Deal at Upscale…
The KT150s sounded great at the start… still sound great… then two weeks ago (4 weeks old), they started to gain upper frequency … not bright… but like the lid came off and the thing was passing super high frequencies. I have Focal speakers with the beryllium tweeters and their response goes up to Jupiter. Then, I have been listening extendedly… working form home and running the amp about 12 hours per day with music for three days. The extended issue is gone. World Trade Federation???
Seriously, how long for these big power tubes to “stabilize”? I never experienced this with my VTL monsters… all new power tubes always sounded great from the start and pretty much stayed there… but then I was using Svetlana 6550 and winged SEDs… Always stable tubes.
BTW, I think you will see way more of these KT150s in bigger tube amps… it really is a good tube.
Bruce in Philly