The PHILCO Phorum
Model 44B - Changes or Bad Parts? - Printable Version

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Model 44B - Changes or Bad Parts? - davemc - 04-08-2018

http://www.nostalgiaair.org/pagesbymodel/581/M0013581.pdf

I am working on a Philco 44B cathedral. Several parts do not match the schematic in Riders. I looked through several Riders volumes (Philco sections) looking for changes pages, as well as searching the internet and the Phorum - but none were found.

For example, the filter choke (part 70) measures 562 ohms. Riders and Radiomuseum says 1750 ohms. I always assumed that such parts are either open or good, and do not change value. Another example: voltage divider 58. Riders says 32 and 235 ohms. Mine measure 24.4 and 257.5 and the values are stable when the terminals are moved. The 24.4 section is -23.75% (the other section is in tolerance). Again, I assumed that wire wound resistors do not normally change values, which is why they were used vs. carbon.

There are 4 flexible wire wound resistors used. One is bad. But the other three do not match the schematic. Part 23 (200 ohms) measures 272.3 ohms. Part 37 (300 ohms) measures 417 ohms. Part 27 (300 ohms) measures 386 ohms. All of these values are stable when the resistor is moved around. I have not removed the sleeves to see how they are actually marked, since unsoldering one end and removing the sleeve would likely destroy the fragile resistor.

Could all of these differences simply be changes, or failure modes I do not understand?

RE: Model 44B - Changes or Bad Parts? - Radioroslyn - 04-08-2018

>For example, the filter choke (part 70) measures 562 ohms.
Have you measured it out of the circuit? I don't see anything that is connected directly to it that would effect it but maybe something down the line. In general 1400 ohm is a lot resistance for the filter choke. Most of the ones I've seen in sets have been a few hundred ohms. Fc generally are in that higher resistance range. Maybe a misprint?

Agree w/the wire wound resistors vs the carbon and would leave them. The acceptation is w/the candohm style, they can show the proper resistance but be shorted thru the metal cover.

GL

RE: Model 44B - Changes or Bad Parts? - davemc - 04-09-2018

Choke 70 is not the main B+ filter choke - that is the job of the speaker field coil. Choke 70 plus a 6mfd capacitor apparently filters the B+ to the local oscillator, I suppose to prevent remaining B+ ripple or changes in B+ load from modulating the LO. But the choke is surrounded by two filter caps which are original, so I will disconnect one lead and re-measure. I was hoping someone else with a model 44 chassis available could measure the same components I mentioned.

The voltage divider power resistor 58 is not a Candohm type - it appears to be wound on a ceramic spool and over-wrapped with cord (I suppose to prevent adjacent resistance wire turns from shorting together). There is no outer metal cover. My experience with those resistors on other Philcos is that they are either OK or one or more section is open.