Hi David256 if you look at many products that use tube sockets they are mounted onto PCB's, and it's not uncommon to have that same PCB have the power transformer attached to it. PrimaLuna tube sockets are mounted on to heavy-gauge fully ventilated standoffs. The chassis is so heavy I don't think there's a lot of microphony going on.
It's so easy to demonstrate. You can whack the hell out of the chassis and hardly a peep will show up anywhere on any PrimaLuna component. Compare that tube a number of preamps where you simply flip a switch and it rings through the speakers.
I do like composite sockets too. We used some killer ones when we built the Ah! Tjoeb CD player that were da bomb. But the ones we use never fail (well, maybe one) so that's what we're shooting for.
On the microphony question, I've found that tubes can lose a little air and harden up with dampers SOMETIMES. Every case is different. Some microphony CAN be good, evidenced by the sound degrading if it's removed. Is it a distortion artifact? Maybe. But that's one of the charming aspects of tubes. If distortion were the end-all be-all buy an Aragon. They are electrically perfect.
If the tube is already low in microphony, and the circuit isn't a silly one (like this idiocy of 27dB of gain in a preamp), and the socket isn't mounted to a PCB, why bother. It should be done on a case by case basis. What ever sounds best. They cost nothing so why not.
