Heater reference

[Nixie]

I want to use regulated DC heaters instead in this hybrid:
http://www.headwize.com/projects/showfile.php?file=gilmore4_prj.htm
My question is, what voltage do I reference the heaters to? The datasheet for the tubes specifies 100 V maximum cathode to heater potential.

 

[poobah]

Reference your heaters to the -400 Volt rail.

 

[Nixie]

Since the tubes are cathode driven, wouldn't the cathode voltage swing quite far from the bottom rail? I thought the -350 shown on the schematic is probably the no-signal idle voltage.

 

[poobah]

If one cathode is pulled all the way down to -400 Volts, it is a reasonable assumption the other cathode does not rise above -300 volts. With the heaters biased reference at the -400 Volt rail. the voltage from cathode to heater should always fall between 0 to 100 volts.