02-01-09: Wireless200
The MP-1 has 18 tubes total. If you got a noisy channel, why not just swap tubes two at a time (between channels) until the bad tube is found? Nine swaps would be the maximum number. Then once the bad tube is is isolated, just order another matched pair?
The MP-1 uses 10 6SN7 and 8 12AT7 tubes. The method you describe is correct. For me, that's a lot of tube maintenance and trouble shooting (remember, I owned one, so I've experienced it).
My situation was complicated by the fact that the MP-1 would have to be uninstalled and removed from my cabinet (and then reinstalled) every time I had to track down a bad tube.
It was a hassle. Everyone has their own level of maintenance they are willing to endure.
If someone is considering this preamp, I would suggest they place it on the top shelf of a rack where the top and sides are easily accessible with a screwdriver.
I still use tube equipment, but the gear I own is a bit shorter than the MP-1, and I can remove the top covers and replace tubes without having to remove most of the components from my cabinet. The MP-1 is too large to allow for this in my system.