I called up this morning, chatted with Frank, and bought the darn thing.
It is not exactly a 550EX. In addition to having the lower wattage, it also has 4 x 2 mosfets = 8, rather than the 6 x 2 = 12 of the 550 and 350.
So, not the same high current, but Frank assures me the present breed of Mosfet (was that Toshiba or Hitachi; which replaced which?), pack plenty of punch.
I meant to ask more about the likely upgrade history of this piece -- how it got to be a 500W fet-valve before getting upgraded to ex output circuits.
I will be driving 4 ohm speakers (PSB Stratus Silvers), which apparently cruise down to 2 ohms occasionally in the bass, but I understand this should not be a problem. There has been no problem driving these with my Bryston B60, which expressly warns not to drive anything below 4 ohms.
The price is certainly right. This was a great opportunity to get a fet-valve amp. I have been reading the steady stream of accolades by Cut-Throat, Eli Duttman, and now Marc Bratton (who did I miss?) on Audio Asylum for several years now, and have long since been persuaded it is the way to go.
Pre-amp will be an FT-LW1 with DACT2 stepped attenuator for now (until the budget replenishes and the right T7 comes along?)
Cheers,
dvb