12AX7 heaters

[changes]

i'm running the heaters of a 12ax7 on DC
my DMM shows 11.5v without the tube and 10.8 with the tube installed
is the tube going to last a lot less???

[R.G.]

It's likely to last longer. As long as tube filaments are fed within +/-10% of the nominal (that is, 13.2 to 10.8Vdc for the 12AX7) the tube will meet its specified performance.

Lower heater voltage will wear the filament out less quickly.

If the heater voltage gets too low, there is not enough electron emission from the cathode to prevent ion bombardment from poisoning the cathode and shortening life.

For beginners, keep it at +/- 10%.

[changes]

thanks for the info
now i'm relieved i won't have to buy tubes all the time for my fender-like tube preamp