Primaluna Prologue One power tube rolling

Always check w/ the manufacturer first! There may be other issues that are not obvious.
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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 would not put kt 88s try the sed wing or mullards

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.)
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