# Treat valve heater as resistive or constant current?

I want to run a 13V(300mA) valve filament from a 6,3VAC transformer, using a voltage doubler(Greinacher circuit).

I am using PSUD2 to simulate the circuit, Which gives me 2 options for the load, either constant current or resistive. Using either I was able to create a source with ~13V RMS output, with 2,2mF capacitances(Which I could get relatively cheaply as bipolar electrolytic).

I would like to know if this could work, because while nominally the voltage doubler should have ~18V output, because of the strong load, the RMS voltage stays 13V. And this already makes some assumptions: What is the series resistance of bipolar electrolytic capacitors of high value(2.2mF)like these? (I assumed 500mOhm).

I expect reality to be different, so I guess I'll have to measure the voltage and correct with some series resistance or voltage divider, but I'd like to know if its possible at all, and how would I go about creating it?

Also is the heater a resistive or a constant-current source? If neither, which one approximates it better?

What other option do I have if any for using this 6,3VAC tap to power the 13V PCL86 tube(Which sadly doesn't have a center filament tap)?

EDIT: I had went on with the voltage doubler, and I got exactly 13V for the heater without any problems. The simulators results were very precise.

The heater is just a resistor. While its cold resistance may be significantly different from its resistance at operating temperature, this shouldn't be important in terms of your modeling. Just use the value $\frac{12.6 V}{300 mA} = 42 \Omega$.