• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

AC Filament Voltage Question ?

An alternative of course is just a plain old resistor. It has the advantage of inrush current limiting to a very expensive valve. Might matter, might not, but can't hurt.

That's my preference also. You can more easily fine-tune the voltage if you need, and as Chris says, the resistor will limit the inrush current when the filament is cold. (Since a cold filament has much lower resistance, the resistor will drop a much greater share of the voltage until the valve has warmed up.)


2011-01-28 2:52 am
I have frequently used both diodes and resistors; even for out put tubes, 811A's 4 amp heaters. Don't find they get very hot certainly not with a driver tube. You can easily work out the size of resistor to use with Ohms law. In Perth west australia the ac voltage is all over the place; supposed to be 240 volts but often rises to 255 volts or more.