Never seen so many Vactrols in one amp. The SLO has 3 or 4. This MK IV has like 10 or more.
I heard they stopped making Vactrols.
I have had this amp 2 weeks & no problems. Ive swapped power tubes 4 times & have settled with some older Sovtek 6L6 WXT's & NOS Amperex in the Pre.. I had those WXT's & 3 other quads if 6L6's stashed for 15 years and didn't know it because most of my amps have EL-34's.
With this amp there is no good or bad just different. Extremely well made.