Apparently, my experience with tube rolling in the M3A is the exception to those previously stated. I've owned the M3 and M3A preamps for about 13 years and only replaced the tubes once in order to gain more midrange warmth and detail. Our local electronics wizard suggested Amperex Bugle Boys. If memory serves they were about $100 each. No question they improved this preamp one to two orders of magnitude. The entire soundstage was much bigger, warmer and more detailed. Mr. Electronics wizard went on to say Russian tubes were designed for industrial use and while they are well-made and typically have long life, they are not intended for audio applications and their sonic characteristics are inferior. I have used tube amps and preamps for almost twenty years and must say the AI equipment is among the most reliable of the various tube equipment Ive owned: BAT, Beard and Herron.