i just picked up a purple stripe simul-class head today. huge upgrade from my dc-5. not nearly as hard to dial in as i thought, it sounded great instantly. well i have been using tung-sols religiously as my V-1 tube but they keep failing on me and i was wondering what preamp tubes go well with the mark 3 and what the tubes assignments are. also, how can i tell how old my amp is? thanks alot!