[Amps] Checking Filament Voltage

[Roger Parsons]

I am busily making a replacement amplifier using a metal/ceramic filament tube.

I would like to coarsely adjust the filament voltage before I install the blower. (The amp is built into an existing cabinet and the filament transformer is a fair way from the tube.) My question is: Is it permissible to run the tube with only filament voltage and no air for a short period? If so, what is a short period?

Thanks

Roger

VE3ZI