How do tube manufacturers like VAC get 55 watts per KT88 where others get only 30-35?


Just wondering how some push pull tube manufacturers like VAC and others get 55 watts per KT88 tube while others are more in the range of 35? Does driving a tube hard like this have any ramifications as to distortion, sound, headroom and tube life? I know VAC amps are highly musical so design, power supply and output transformers obviously contribute much to overall sonics. A company like Zesto gets about 25 watts per KT88 but uses a class A push pull circuit rather than class AB.  This seems like an attractive design.
I guess, as always, it's all in the implementation. Thank you for helping me to better understand.

normie57
I would still love to know how VAC gets 100 watts per pair of KT88s without tube reliability issues or distortion. Probably some proprietary secrets, the intelligent auto bias,  as well as huge power supplies to comfortably generate the needed plate voltages.  I have heard Kevin use The Signature 200 IQ in monoblock configuration at a couple of shows and the sound was memorable.  I'll place an order and give them a spin in stereo first.  I would also love to hear from Zesto amplifier owners, either the Bia 120 or Eros 300.  Thanks so much!
I don’t know about Kevin Hayes and his VAC designs, but Roger Modjeski details how he gets 100 watts out of a pair of KT88’s in his Music Reference RM-200 in the company’s now-dormant AudioCircle Forum. I know MR isn’t as hip and cool as VAC, but what Modjeski has to say may still be found to be of some interest and/or value.
normie57,

Didn't know if you were still interested in the VAC 200 IQ, but one just one up on audiomart at a great deal.  Any updates?  Keep us posted.
I've heard the 200 iq and it is pretty amazing - the clarity, transparency yet body and realism that Kevin Hayes gets out of that design is mind boggling. The flexibility of tube rolling with the auto bias does make it one of the most user friendly amps on the market.