Run the filaments for a minimum of half hour before applying high voltage.
You don't mention what tube you are speaking about, but if it is an Eimac,
go to their website and read their technical information.
http://www.cpii.com/eimac/index.html
The information is good no matter who made the tube(s).
According to RCA, run the tube filament only for 30 minutes. Then run it
with reduced grid drive for 30 more minutes. Then run it at full grid drive
and reduced plate voltage for 30 minutes. Finally run it at full grid drive
and full plate voltage.
Don K4KYV
