March 11, 2021 at 1:39 pm #16391
Hello I am working on an National Carbon Co. Model 31 Eveready radio ,well looking in the power supply to change the caps I see that some one has cut one of the wires going to
the plug for the field coil power supply,there is another plug on the radio side for the voice coil ,anyway where the wire for the power supply was cut some one put a 4.7 K power resistor
across the leads to take the place of the field coil ,I think these radios had a switch that you flipped over , one side when you use the speaker they sold that had a field coil and the other
side when you use a magnetic speaker ,I know when you replace a speaker with a field coil for a magnetic speaker you put a resistor across the power line that goes to the field coil
part of the speaker ,there is a hole beside the plug for the power supply for the field coil but there is nothing there ,could be some one along the life of this set took out the switch ?.
What I would like to know is the 4.7 K power resistor too big should it be lower ? . I found a United American Bosh Corp. schematic that shows a very near the same model radio
and the power supply for the field coil on that set is hooked up to the line coming into the radio at 110 volts , most of the sets that I have changed the speaker over to magnetic get
maybe 85 volts for the field coil and a 1K power resistor seems to work fine ,would be thankful for any input ,take care all the very best Rick
Schematic for the radio = http://www.nostalgiaair.org/pagesbymodel/135/M0040135.pdfMarch 14, 2021 at 12:46 pm #16430
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 RickMarch 14, 2021 at 2:08 pm #16433Sterling SpurrellCVRS Member
Hi if you go to page 222 it shows the Eveready 30 series info and you read down through it shows a field resistance of 5000 ohms https://worldradiohistory.com/BOOKSHELF-ARH/Bookshelf-Gernsback/Gernsback-Radio-Service-Manual-Vol-1.pdfMarch 14, 2021 at 5:22 pm #16439
Thanks so much Sterling , how did you ever find that info, I will for sure save that page , the info I need is on page 221 ,it,s the resistor # R-10 that I was looking for ,it says that it takes the place of the field coil ,I have a 10 watt 3 K on hand to use ,it calls for a 2500 ohm resistor , do you think the 3K – 10 watt should be ok to use ,again thanks so much ,take care all the very best RickMarch 15, 2021 at 12:23 am #16440
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