Always check w/ the manufacturer first! There may be other issues that are not obvious.
FWIW, the dealer initially said you could also run 6L6's in the One, so I tried it out. Initially I had no problem 'til one day I left the amp on continuously for 12 hours. I was out of the room for the last 6 hours. I came in and the sound was 'dark' and the sound stage was closed in. Highs were rolled off and the sound generally muffled. It wasn't subtle. Short story - I turned off the amp and turned it back on about 30 minutes later. The problem was gone. I assumed that the auto bias curcuit was the problem (and I still think that is so). You will note that no where in the manufacturer's literature does it say that you can use 6L6's, only EL34's, whereas in the Two it includes 6L6's and KT88's. Obviously there are more changes in the two amps than the simple ones that mentioned in the vendors descriptions. I reverted to EL34's. Anyway, thats my experience.
What experiments have you made with the small tubes - fertile ground there for tonal changes.
I didn't like the EH 6CA7s. They were grainy and sterile sounding. They lost the liquid tone of the Svetlanas.
For 12ax7s I've tried JJs (too bloated), EH (pretty decent), Groove Tube Mullard clones (my favorite current production tube so far), NOS Brimars (very nice), NOS Phillips branded Mullards (even nicer), and NOS Amperex Bugle Boys (my favorite).
I was going to suggest you try Telefunken 12AX7's but the Amperex are very similar (BTW, you don't HAVE to buy "Bugle Boys". All the Amperex/Holland tubes are the same, and they made them for a multitude of other brands/manufacturers: Hewlett Packard, Eico, Fisher, Electrohome, even Mullard -- if you look on Ebay, you'll see what I mean)
If you really want a big (and pleasant) surprise get some NOS (ca. 1958) RCA longplate, blackplates. The best 12AX7 I've heard, and maybe the best 12AX7 ever made (see discussions on AA.)
I have the Prima Luna 2 integrated and Prima Luna 5 power amps. When I upgraded preamp tubes, Kevin Deal (Upscale owners) suggested NOS 12AU7 Sylvanias and 12AX7 Mullards. Excellent upgrade.
As for the power tubes, it is recommended to only use the EL-34 with the P1 (look at Upscale Audio's web-site). The P2 supports tube rolling.
Hey guys, I thought I'd clear things up a little for you...
The ProLogue One along with the Four, Six, and new DiaLogue One are optimized around EL34 power tubes. However, you can also use 6L6GCs, KT66s, KT77s, 6CA7s, 6V6GTs, 7581s. We have had dozens of customers run 6L6GCs or KT66s with great results.
You can use KT88 & 6550 types too and they'll work just fine, however those tubes have higher dissipation, and require a slightly hotter bias to function optimally.
Since the ProLogue One, Four, Six, and DiaLogue One are optimized for the EL34, we do not recommend using KT88 types, but you can do so if you feel like experimenting.
Newbee, I am not sure exactly why you would experience what you did. I can say with confidence it was not the Adaptive AutoBias board. If it was, the problem would repeat itself, and typically would not take 12 hours to manifest. It could be one of the 6L6s had what we like to call a "hiccup" that may have manifested while playing, then dissipated once the tube cooled off.
Adaptive AutoBias is the main reason you can use a wide variety of power tubes. They don't need to be matched, and in fact, they don't even need to be the same tube type! You could have one EL34, one 6L6GC, one KT66, and one 6V6GT plugged into the ProLogue One, and Adaptive AutoBias will recognize the different tubes, and adjust itself accordingly so the amp is running at optimum levels. Now... it may not sound so good, but it will work!
This can be very helpful if you're having a little gathering and one EL34 craps out on you and all you have lying around are some 6L6s or KT88s.
Of course if you ever have concerns about whether or not a tube will work, feel free to shoot us an email and confirm. As with any piece of tube gear it's always better safe than sorry!