I did spot one time , an Audio Research ,I think it was , Twin Mono Bloc , 16 6550's per box , close on 1kw of tube power p/ch.
was only a few grand , I think it was the equivalent of 2000w of heat output just idleing ;D
It basically needed a cooker supply cable per channel from the mains box or you would suffer voltage drops at moments of peak power.
Its been a while since I read the article , he doesnt seem to give much data on the output transformer wind , probably not difficult too do if you found a suitable pair of cores from scrap though,