Heater to cathode voltage limits in cascodes???

[grhughes]

I want to experiment with cascodes. I've got some military pulls 8532/6j4wa. If the two tubes in cascode are in different envelopes then doesn't that raise the heater to cathode voltage limit? I still should use two isolated filament windings? Thanks a whole heap! Ray

 

[EC8010]

If your upper valve is in a different envelope it can have a separate heater supply. Instead of placing the strain of the elevated cathode voltage across the heater cathode insulation, you now strain the interwinding insulation of a mains transformer - which is far more capable of withstanding it.