Replacement coil for a field coil - Printable Version
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+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Various and Sundry Categories (https://philcoradio.com/phorum/forumdisplay.php?fid=37)
+--- Forum: Other Radios (Non-Philco) (https://philcoradio.com/phorum/forumdisplay.php?fid=12)
+--- Thread: Replacement coil for a field coil (/showthread.php?tid=22297)
Replacement coil for a field coil - onlyrick - 03-14-2021
Anyone have a National Carbon Eveready model 31 or another model ,if so could they please measure the field coil and see how many ohms it is or if they know the value of the resistor inside the power supply that is switched on when you use a magnetic speaker ,some one along the way took out the switch that you flip back and forth ,one side when you use the speaker sold with these sets that has a field coil in it and one side when you use a magnetic speaker ,who ever took out the switch and resistor on my set put in a 4.7 K power resistor going across the plug for the field coil , I think that a 4.7K resistor is too high ,any speaker with a field coil that I have replaced with a magnetic speaker I used a 1K power resistor to take the place of the field coil ,would be thankful for any help all the very best take care Rick
RE: Replacement coil for a field coil - RodB - 03-14-2021
If you have to resort to trial and error, you can start with a 2k resistor measuring the plate voltage of the first AF tube and make adjustments to get about 100 volts.
RE: Replacement coil for a field coil - Radioroslyn - 03-14-2021
Or you can use a rough calculation of 10 ma the rf, det, & 1st audio. Measure the voltage @ the right side of 2352. Subtract the voltage you are looking for (100v). This is the voltage you need to drop or get rid of. I use an online calculator to do you work as my brain is mush. https://ohmslawcalculator.com/ohms-law-calculator Voltage = the voltage you want to drop. Current = 10 ma. If you click on the down arrow you can set the current for ma rather than amps. Hit calculate it will tell you the resistance and wattage you need. Always triple the wattage unless you like flaming hot resistors.
Come to think of it since you have a resistor in there you could calculate the current using the voltage drop. This maybe a bit more ecu rate than me guessing...