which 6sn7 tube for my wyetech topaz amp

Of all the 6sn7's I have and I have most of them, I always go back to the sylvania 52 bad boys in my preamp. The red base 5692 are also very nice.

In your amps it could be a different tube, but these two are a good place to start.

Bigshutterbug, those Sylvania's you mentioned aren't from the 40's they were only made from 51 to 53.
Those are the ones I recommended in my post above.
Excellent tubes!
Joe