Rolling KT150s in Primaluna hp integrated

jb
I totally get your excitement, I have been in the same boat with the PL HP Integrated and rolling the stock PL pre 12AU7s to NOS Mullards/NOS Brimars and the EL34--> KT88s. 

As you said, swapping out the first 2-4 pre tubes makes critical sound changes, for the better for sure. I have floor standing speakers, so my next move would be to move up to the KT120s and keep the Mullards in the first two inner pole positions of the pre tubes, followed by the Brimars, then the 2 stock tubes. Since the KT120s would spread out its energy toward the highs/low, the Mullards would fill in the mids nicely.

But alas, I live in a place without AC that gets so hot in the summer that tubes are now "temperature-prohibitive". I will be having to sell the HP integrated to go to Class D ... scary.

@georgehifi  PrimaLuna emphasizes that they run their tubes about 1/2 -2/3 as hard as other manufacturers in order to NOT overrun the tubes, especially since PL encourages listeners to tube roll with expensive NOS tubes. I believe the amp also gets a more stable load and presumably lower distortion with not running the tubes so hard and hot. 

@a25105 In the Sta Cruz Mtns, gets up to the high 90s and tops 100' as well. problem is, I live in an old barn converted into a home with cinder blocks under the wood siding. Absorbs heat like a mo-fo. No AC. I would come home from work and not be able to listen to my system! And no plans to move soon.
But the heat from the PL Integrated is from the tubes and the 3 Large Transformers hiding in the back under the metal cover .... 

@georgehifi as you said, the bias can change the heat. that is why PrimaLuna has a "self-bias" to not run the tubes as hot. we can argue over specifics, but it is the essentially the same concept, of ultimately, how hard the tubes are run. The bias of any amp will effect the tube heat, not just PL. it is the manufacturers call for self-biased units, but the owners call if manually biased. In any case, it is true that tubes will live different number of hours, eg 5k vs10k, depending on the supportive electronics/bias adjustments.

@tubegroover @georgehifi . sending your USED tubes in to be cryo'ed may not show clear difference in sound. this is b/c "cryo'ing" tubes essentially hardens some metal structures of the tubes. these structures, metal pieces, etc will harden over time anyway with use. 

So there would be a bigger difference b/w 2 NEW sets of tubes, one Cryoed and one NON-cryoed. But if you are sending in used tubes for cryo'ing, I would ask:
how many hours do they have on them? what is their expected life span in the particular amp you are using? eg, if a used tube has 4000 hours on it, and the life expectancy is 5000 hours, then it will already have been "broken in", in terms of the metal structures hardening. Sending it in to be crayoned with 4k hours would not make a significant difference IMO.