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Philso 45 Resistor Part 21 - Printable Version

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Philso 45 Resistor Part 21 - IamZoot - 04-20-2026

The schematic I have says the value of this resistor is 200 ohms.  The parts list says it is 500 ohms.  The one in my radio measures at 400 ohms.  Is there a known correct value for this part?  What is the wattage rating for this item?

RE: Philso 45 Resistor Part 21 - DaleHCook - 04-20-2026

IamZoot Wrote:  The schematic I have says the value of this resistor is 200 ohms.  The parts list says it is 500 ohms.  The one in my radio measures at 400 ohms.  Is there a known correct value for this part?  What is the wattage rating for this item?

You need to look at all of the service information, and look at it closely. The schematic in the first 1928-1936 Philco Yearbook, p. 53, has "Note: Resistor (21) is 500 ohms in current production." Service Bulletin Changes 1:2, in an entry dated 15-Jun-1934, shows that in Run 5, Part 21 was changed to 400 ohms, as well as showing other changes in Runs 6, 8, 9, 15, and 16. Service Bulletin Changes 2:2 shows additional changes in Run 15.

The 1936 Philco Parts Catalog, p. 9, shows that the 500 ohm resistor (Part 6977) and the 400 ohm resistor (Part 33-3016) are both flexible wirewound resistors rated at 1/2 watt.

RE: Philso 45 Resistor Part 21 - IamZoot - 04-20-2026

I appreciate the info. I guess I need to do a deeper research when a question like this comes up. Which brings to mind, why a wirewound resistor? I need to replace this resistor and see no need for one that is wirewound unless they did not want to have any resistance change expected from a carbon one.

RE: Philso 45 Resistor Part 21 - DaleHCook - 04-20-2026

We have have Philco service information which is the most complete that you will find. To find it use the Philco Service Info Index.

Whenever possible I use the manufacturer's service information, rather than Rider or Beitman. I have manufacturer's service information for all of my Philco, Zenith, and RCA radios.

RE: Philso 45 Resistor Part 21 - patrician56 - 04-20-2026

Hi IamZoot,

If you take a look at the Philco parts catalogs (In the Philco Library - tab at the top of the page - then under the PARTS tab) and then look at the resistors listed (I was looking at the 1936 Philco parts catalog - pages 8 & 9) you will find that all but 2 of the cartridge type (carbon - dog-bone) resistors for all of the wattages listed (1/4w, 1/2 w, 1w, 2w, &3w) have ohm values above 1,000 ohms.

Page 9 lists the wire-wound "flexible" resistors. All but 5 had ohm values across the different wattage values (1/3w, 1/2w, 1w, and 2w) between 2.5 ohms and 1,000 ohms.

So, it appears that if they needed a resistor with a value between 2.5 and 1,000 ohms, they chose a wire-wound resistor and if the requirements were for a resistance between 1,000 and 10,000,000, they went with the cartridge type.

I believe that I read somewhere that until the mid '30's carbon resistors with a low ohm value were not that good so the wire-wound flexible resistors were used.
Good luck with the project!
Fran Mayer

RE: Philso 45 Resistor Part 21 - morzh - 04-20-2026

I at some point of my life was surprised to find out that wirewound resistors can go to GOhms, not just MOhms.