I cannot comment on the Silver Sevens. I do, however, own the Carver Crimson 275 amp, which carriers a long warranty on tubes. I have made some amps and modify stuff for fun. I can tell you that, while I'm not familiar with the circuits involved in that amp, in the 275 he uses a DC restorer circuit that is essentially lifted from television technology of yesteryear. People were tired, presumably, of their TVs being "on the fritz" so they introduced the DC restorer to that product. It may have been created way before for all that I know.
The DC restorer regulates power so that big power tubes-a la KT 120s--can idle at <10 watts. This results in efficiency and the tubes last for years.