If you are firing up the tube for the first time in many years, let it
bake
with full filament voltage for a few hours to allow the vacuum to
stabilize
and degas.

I have done that and all still appears well. Even found a 10 volt, 16 amp
transformer
in the junkbox. Before I commit to using these tubes in a HB amp I will see
if they pull
plate current, and use a grid bias supply to control current. I have a
variac to control
plate current.
Tnx

Rick K2XT