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Identifying 1938 resistors - Printable Version

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Identifying 1938 resistors - DuMont - 04-18-2020

Can anyone provide a positive ID on these resistors?
They came out of my 38-3.
I believe the large one on the right is supposed to be a 7500 ohm and the smaller one on the left should be either 9 k or 32 k; I lean more toward 9 k.
Both of them currently measure at 10.15k and 10.21k respectively.

RE: Identifying 1938 resistors - rfeenstra - 04-18-2020

I would agree with your analysis! 7.5K and 9K.

RE: Identifying 1938 resistors - DuMont - 04-18-2020

Thank you! So the large one is 7.5 k and the smaller is 9k. Wow. They've done a bit of drifting over the decades....

RE: Identifying 1938 resistors - Ron Ramirez - 04-18-2020

https://philcoradio.com/library/index.php/shop-talk/general/how-to-decipher-philco-resistor-part-numbers/

RE: Identifying 1938 resistors - DuMont - 04-19-2020

Thank you Ron! Very helpful! I'm curious though - why is the larger of the two resistors shown supposed to be 7500 k while the smaller is 9 k?

RE: Identifying 1938 resistors - DuMont - 04-19-2020

and even smaller than the 9k is a 32k ohm resistor. It's kind of like wire gauges? The higher the gauge, the smaller the wire? So the higher the ohms, the smaller the resistor?

RE: Identifying 1938 resistors - rfeenstra - 04-19-2020

The physical size of a resistor determines the power handling capability. The large resistor is capable of dissipating much more heat than the small one. It is, undoubtedly, used in the power supply section of the radio to drop the B+ voltage. Such an application may generate 2 to 5 watts. Much more than that and they usually would use a wire wound resistor because of its greater power handling capability. The smaller resistor is probably only capable of dissipating 1/2 watt of heat. You can easily find a 7.5K resistor that is the same size or even smaller physically than the 9K resistor. The amount of power that a resistor must dissipate is determined by the amount current that has to pass through it. That current is determined by the ohm value of the resistor and the voltage drop that occurs across it.

RE: Identifying 1938 resistors - DuMont - 04-19-2020

Ok, now I remember. Hearkening back to my 9th grade science class!