@porchlight1
When you say Sylvania "triangle Plates" I beleive you are referring to the angled T plates in the GTB series? They started in 1954. Not as good as the previous GT series, but still great quality Sylvania tubes.
Tube Pre-amp Suggestions.
I have a Coda No 8 power-amp and was looking for some suggestions on what would a good tube pre-amp that would pair up with it?
https://coda.cc/coda-no-8-amplifier
Thank you!