@orthomead I didn't know that one could just drop in a KT150 quartet in at all or with modification. The amp is rated 100 watts per side with a quartet of KT88s (which VAC claims they achieve tapping 3 tube elements instead of just the plate and filaments)
KT150 should provide at least 100 watts per side and probably much more with VACs 3 sided tube power.
Do VAC amps tubes burn up quicker using getting max power out of them?