Hello All,
Does anyone know the values of the resistors in the Fada 115.23 ballast tube. It's missing from the chassis I'm working on. I am assuming that the dial lamp is a number 47. The tubes all have 300 ma filaments, however the 47 dial lamp has a 150 ma filament. I believe that, if there was no dial lamp the ballast resistor would be 194 ohms at about 20 watts. But the other section I'm not sure of.
Please help if you can.

Thanks,

Dave

The lamp shunt resistor needs to be 42 ohms (6.3 V @ 150 mA) When paralleled with the #47 bulb, this will give 300 mA through the two. When you calculate the value of the main series voltage dropping resistor, just add 6.3 V to the sum of the individual tube voltages and subtract the total from 120 V to determine the voltage drop that the main resistor needs to provide at a 300 mA string current. Remember to derate the power resistor by 70% to ensure longevity.

Dave

Original ballast drops 55 volts @ 300 ma. Resistance element is between pin #3 and #7 with a lamp tap on pin #8.

Although the part number was only used by Fada ballast configuration is fairly common. Might find a sub here:

http://www.oldradioparts.com/2a2fl.txt

Norm

:The lamp shunt resistor needs to be 42 ohms (6.3 V @ 150 mA) When paralleled with the #47 bulb, this will give 300 mA through the two. When you calculate the value of the main series voltage dropping resistor, just add 6.3 V to the sum of the individual tube voltages and subtract the total from 120 V to determine the voltage drop that the main resistor needs to provide at a 300 mA string current. Remember to derate the power resistor by 70% to ensure longevity.
:

Norm,
I think the BALLAST number is K55C.

Thanks,

Dave
:Dave
:
: Original ballast drops 55 volts @ 300 ma. Resistance element is between pin #3 and #7 with a lamp tap on pin #8.
:
: Although the part number was only used by Fada ballast configuration is fairly common. Might find a sub here:
:
:http://www.oldradioparts.com/2a2fl.txt
:
:Norm
:
:
::The lamp shunt resistor needs to be 42 ohms (6.3 V @ 150 mA) When paralleled with the #47 bulb, this will give 300 mA through the two. When you calculate the value of the main series voltage dropping resistor, just add 6.3 V to the sum of the individual tube voltages and subtract the total from 120 V to determine the voltage drop that the main resistor needs to provide at a 300 mA string current. Remember to derate the power resistor by 70% to ensure longevity.
::
:
: