Conserving our good CRT's

[Zenith26kc20]

If memory serves me right, General Electric did studies on operating tubes at different filament voltages. Too high killed the filaments, too low the cathodes. Somewhere I have data on this involving the GE "five star" tubes.
I remember reading that the cathode surface was not uniform in temperature at lower voltages and the hot spots died off earlier.
A friend of mine tried that idea on apower amplifier. He ran the filaments at 5 volts instead of 6.3 volts and it resulted in the rapid demise of four M & O valve company (Genalex for the audiophiles) KT88 output tubes.
CRT cathodes are different in construction but the principle is the same.