[Amps] Switching PS for filaments?

[rgroh at swbell.net]

Ok, how about pulling all the treads together on this topic and both summarize and visualize an ideal filament supply -
1.    Regulated DC voltage - low noise

2.    Voltage output settable to accommodate different tubes *

3.   Output current is both controlled (will take care of turn on) and limited - current limit settable to accommodate different tubes

4.    Ability to interlock with other control circuits to, for example, ease implementation of delaying application of HV, interlock with blower,  delaying turnoff for cooldown. 

5.    It would be neat to tie all of this plus the voltage settability* to allow even more flexible operation such as standby operation (i.e. running in a 'almost ready' to go on the air - filament running at lower voltage, no HV applied, etc, low speed on fan and then, with one switch contact, be up full and ready to go in a couple of seconds).

There has been a lot of discussion about whether or not controlling current on start is good, whether running filaments at lower voltages will prolong tube lifetime, etc. There is certainly debatable aspects of these factors but probably two points would be admitted by most (if not all) of us:
1.    Controlling filament current surge on startup can't hurt
2.    Delaying HV application until filament is up to temperature and stabilized can't hurt
3.    Having a cool down period can't hurt.

Agreed?

73
Bob, WA2CKY