I tried loads (well into double figures) of power amps with the Primes and I didn't find any valve amp that sounded as good as a Nelson Pass First Watt J2. The Canary 300B push pull mono's just didn't do it. Coco's SIT amp the Mk II version surpassed the J2 with some ease and remains the standard to be aspired to as far as those speakers are concerned.
I do have a Sony v-fet power amp which is also makes a fist of driving them, but still trails in the wake of Pete's creation.
Needless to say, all of the good sounding SS amps were class A.
Harbeths are just zzzzzzzzzzzzz btw.