How to calculate heater to cathode voltage?

[CoffeeTones]

What is the proper procedure to calculate heater to cathode voltage of the CF?

Thanks

[epis]

There is no need for calculation,just measure it, heater is most often referenced to the ground - 0V. But if you want to raise heater potential, it's voltage difference between cathode and heater.
You can find max allowed voltage cathode - heater in manufacturer's data sheets.

[CoffeeTones]

Ok, but please explain how to use the information. Is it simply to measure voltage at pin 8 of the 12AX7 CF and have it not exceed the heater to cathode rating of the tube data?

[epis]

Yes, that's right.
To prevent the problem of exceeding max voltage, most people are making divider from B+ voltage.

[Firestorm]

Yes, that's right.
To prevent the problem of exceeding max voltage, most people are making divider from B+ voltage.

I wouldn't necessarily say "most" people. If the supply voltage is made too small, the cf won't do the current stealing thing Merlin Blencowe describes. I prefer to raise the heaters using an appropriate DC bias.

[CoffeeTones]

My supply is 320V and cathode can be between 185V and 200V depending on the tube and the preceding gain stage' cathode resistor value of 820r to 1.2k

I'm using 100k anode resistor here and don't really want to go lower than 100k for the load resistor off pin 8.

Do you have a link or information on raising the heaters that you might share?

[Firestorm]

My supply is 320V and cathode can be between 185V and 200V depending on the tube and the preceding gain stage' cathode resistor value of 820r to 1.2k

I'm using 100k anode resistor here and don't really want to go lower than 100k for the load resistor off pin 8.

Do you have a link or information on raising the heaters that you might share?

See here:http://www.valvewizard.co.uk/heater.html

Tap a well-filtered B+ node (the screen supply or later), voltage divide to the DC level you want. Add the cap to futher filter the DC if you want, but it works without. This is also useful to quiet hummy tubes used with very small cathode bypass resistors or run unbypassed. Can help kill heater induced hum in SE output stages, too.

[martin manning]

Yes, that's right.
To prevent the problem of exceeding max voltage, most people are making divider from B+ voltage.

I wouldn't necessarily say "most" people. If the supply voltage is made too small, the cf won't do the current stealing thing Merlin Blencowe describes. I prefer to raise the heaters using an appropriate DC bias.

That is what epis means- use a divider from B+ to create a DC voltage to elevate the filament circuit:

[Firestorm]

Yes, that's right.
To prevent the problem of exceeding max voltage, most people are making divider from B+ voltage.

I wouldn't necessarily say "most" people. If the supply voltage is made too small, the cf won't do the current stealing thing Merlin Blencowe describes. I prefer to raise the heaters using an appropriate DC bias.

That is what epis means- use a divider from B+ to create a DC voltage to elevate the filament circuit:

Ahh, I misread him. Sorry epis.