Preamp tube DC heater circuit

[Nigel Goodwin]

Now you got me going. Why bother twisting filament wires if the OP is powering them on DC? Twisting the filament wires is supposed to be a hum-bucking technique, but it can only apply if the filaments are heated with AC.

Quite right - no need to do it for DC heaters - wxcept it looks pretty cool

 

[Roff]

Won't it stop externally induced currents INTO the heater?

Potentially, but the heater/cathode thermal time constant is so long that any current induced would not have a measurable effect on cathode emission.