12AX7 Heater Wiring

[A.Gillies]

I know the answer is probably around somewhere but I can't find it. If you were wiring a 12AX7 for 12v heater operation and had say an 18v supply, you would connect + and - to pins 4 and 5, would you only need the resistor on the +, right? Sorry if this a silly question or if it has already been answered or both. Thanks!

[frequencycentral]

7812

[defaced]

Assuming that 18v is DC, use a 7812 regulator like FC said. Only connect the pins 4 and 5. Pin 9 is not connected for 12v operation.

[PRR]

I'll disagree. This is a job for a resistor. 5.4V at 0.15A is 36 ohms 0.81 Watts. Use two 75 ohm 1/2W resistors in paralel.

Put the resistor on whichever end is easier.

If you have a very leaky tube, there is a slight preference for putting the resistor in the "-" lead. But a stronger preference for using a healthy tube.

If you are using a very hashy power supply, put the resistor on the + end of the heater and add a 100uFd cap to ground, to reduce the power-hash being leaked off the heater feed into the amplifier paths.

[A.Gillies]

Thanks for the help!