Lew, absolute congrats! You will not be disappointed. My opinion is that these amazing amps just happen to be the finest tube amps in today's world. I believe they are the most powerful and are more powerful than many SS "super amps". I have always believed in the Agostino Rule: unless an amp is truly pure Class A, for a SS amp to sound its best, it should operate at no more than 10% its rated power.
For a 1.25KW, this would be a maximum of about 140-150 watts, which is adequate for most source material. So since the 3500 will do over 500 watts, it is a considerably more powerful amp. SS amps have a tendency to sound hard when pushed, whereas tube amps remain sonically consistent at clipping.
IMO, the exception to the Agostino Rule is the Class-A SS amp. Many amps that purport to be "true Class-A" aren't. The Accuphase A-250 is true Class-A. But look at the wattage you get: 100 watts at 8 ohms true Class-A. Pass Labs XS300 is another true Class-A amp: 300 watts at 8-ohms, weighs in at 306 lbs/ch and 900 wats power consumption when not in idle. There are other Class-A amps. These amps, IMO, do not become hard or change sonically when pushed to clipping.
This is why "tube watts" are considered more powerful than "solid state watts". However, even most true Class A amps become Class-AB as they approach clipping and thus avoid clipping.
The weakness of virtually all tube amps is an ultimate lack of power. Ultimately watts really are watts as demonstrated by the below pic. No tube amp other than a MC3500 will play this cut at a high level. It will blow them up. But any high-powered SS amp will easily handle the drum on this Wilson CD: Winds of War and Peace: Liberty Fanfare. Now if you are foolish enough to play this through your system at a high level, be prepared to blow up your amps and speakers. :yes
It is impossible to catch the maximum needle excursion, but it certainly is over 400 watts. Volume 68% D-1100. It is loud. Many SS amps will buckle with this drum. No tube amp other than a MC3500 will handle this drum. It will blow it up, literally.
Best
Charles
p.s. the VAC Statement 452i Monoblock rated at 450w/ch, clips at 183 watts into a 4-ohm load. A pair will run you 150K. Reviewed by MF, 4/18, Stereophile:
"VAC specifies the Statement 452 iQ's maximum power when used as a monoblock as 450W into 4 ohms (23.5dBW). With our usual definition of clipping, which is when the output's percentage of THD+noise reaches 1%, the VAC clipped at 235W into 8 ohms (23.7dBW, fig.4, footnote 1). However, less power was available into 4 ohms at 1% THD+N: 183W (19.6dBW, fig.5), though 370W was available at 3% THD+N (22.7dBW) and 410W at 10% THD+N (23.1dBW)."
Many tube amps will only barely meet their published specs. Going back to the 1960's, all Mac tube amps are
guaranteed to meet or exceed their published specs for the life of the amp.