Hi Peter,
If cleaning the sockets still leaves you with noisy or intermittent connections, the QQQ sockets you can get at PCX and other places are very nice, have a death grip on the tube pins, and are very reasonably priced compared to other boutique tube sockets. They come in noval and octal only, which is fine for the Crack, but I sure wish they'd come out with an UX-4 version.
HTH,
Jim
Jim Rebman -- recovering audiophile
Equitech balanced power; uRendu, USB processor -> Musette DAC -> 5670 tube buffer -> Finale Audio F138 FFX -> Cain and Cain Abbys near-field).
s.e.x. 2.1 under construction. Want list: Stereomour II
All ICs homemade (speaker and power next)