Starting work on a GE 800 Locomotive.

[Electronic M]

Originally Posted by Bill Cahill

As a matter of fact, I believe that is why the company painted those connections.
That chassis definitely needs a complete re capping.
Those filament have me stumped. Sams only says 75 ohms. But hose resistors change resistors change resistance as they warm up. So, I'm mixed up as to what values of resistors to put in there.
Bill Cahill

To get the correct 'hot resistance' (which is what you want to use) use the schematic to determine the tubes in the string, add the heater voltages of those tubes (you will get a more accurate sum if you go by the datasheet heater voltages), subtract the sum of the heater voltages from your AC outlet voltage (or a reasonable reckoning of it) to get the voltage the resistor needs to drop. take that voltage and the heater current of any tube in the string and use Ohm's Law (R= E/I) to find the resistance.
You can find the power by P=EI, P=(I^2)R, or P=R/(V^2)...Probably good to double that value as many power resistors get hot enough to unsolder themselves when they reach rated power.

If you are worried about achieving a soft start, you could round that resistance up a bit, and or add a CL-90 inrush current limiter to the set.