heater warmup and b+ delay

[SemperFi]

I've always been careful to warm the heaters before applying b+ because I'm a sensitive guy.
Lately I've been confronted with some notions implying that this is nonsense on indirectly heated tubes.

I've always thought that even indirectly heated tubes need the electron cloud around the cathode (space charge) to provide protection from ions and other bad stuff in the surrounding nether before applying high voltage to the plates.

No text in manuals/books exists (in my search) regarding indirect-heaters and high voltage. The heater cathode is always mentioned in a by-note in passages regarding other cathode types.

Please check this link out before replying:

http://www.freewebs.com/valvewizard1/standby.html

I would be much happy if I can eliminate the bothersome standby switch and all worries surrounding the issue.

Thanks

[Eli Duttman]

The issue is cathode stripping. Below 400 V., cathode stripping is (IMO) pretty much academic.

In an amp with "fixed" bias O/P tubes, an instant on, SS rectified, bias supply will prevent cathode stripping, as long as B+ rise is slightly delayed. A NTC inrush current limiting thermistor supplies the requisite delay, when SS or directly heated vacuum rectification is employed. Vacuum rectifiers with cathode sleeves automatically exhibit a slow B+ rise.