Quicksilver Mono 100's

I am considering the Quicksilver Mono 100's as amps for my Quad 988's. However, there is something I don't really understand about these amps. The amps produce 100 watts per side from only two KT88 or 6550 tubes. The total tube compliment is: 1 12AX7 input, 1 12BH7 driver, and the above mentioned output tubes. I don't understand how they get 100 watts out of just these two output tubes. Are they cooking those tubes with high voltage? Running them into class B? What are the implications for the sound of this amp? Has anyone spent time auditioning it? Thanks.
Hey Peter- I think they must be running in Pentode if he's getting 100 watts per pair out of them. If you want to know more about the design try contacting Mike Sanders through his site. Phone is best, but you can also email. I've found Mike can be pretty brief and to the point in his email answers though. The same two KT88's give his older Silver 90 monos 90 watts per side in Pentode so it's not a far stretch to 100. Don't know how he does it, but it must be in Pentode I'd guess. Of the four Quicksilver pairs I've owned, the Silver 90's were the most punchy and probably the least refined/musical to my ears and for my tastes. Still a nice set of amps and good for rock and symphonic stuff. Depends on what you like to listen to most. The other stuff I've owned of his had a better sense of air and atmosphere and depth, and I'd prefer any of the three better over the Silver 90's. One is SET, one Push/Pull and the third was also triode but using EL34's. If we hook up when you come to Seattle you will get to hear the SET. Looks good for the 14th as I found out we are actually leaving on the 16th. I'll get in touch later tomorrow.

high biased beam tetrodes do produce 100W per pair.
the question than lies in its longetivity and overall reliability of the component.
I have owned both the 8417 and silver 90's but am not familiar with the 100's. The Silver 90's were spec'ed to be biased quite high-100ma which puts them at about a Class A design, I think (I'm no techie). I ran mine at 80ma to save tubes and didn't notice any sonic degradation. Quicksilver estimates tube life to be 1000 hours and I have found this to be fairly accurate.
80ma is still high bias current but the good thing that you need to retube with 2 tubes per channel instead of eight or more.
as far as i know quickies have pretty solid circuit protection in case the tubes goes bad to blow grid resistor first before it goes to the plate shortage.