The PHILCO Phorum
37-620 Mystery Part - Value? - Printable Version

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37-620 Mystery Part - Value? - davemc - 01-23-2011

http://www.nostalgiaair.org/PagesByModel/212/M0013212.pdf

I have a question about part 34, listed as a 400 ohm bakelite resistor. It is in the cathode of the IF amplifier. What is installed (and appears original - in fact ALL parts of the radio are original) is a flexible resistor with code RED, BLACK, BROWN (body, end, dot). If this were a normal resistor it would be 200 ohms. But I don't know if the codes for flexible resistors are the same. It measures 810 ohms - likely too high. The value is stable (does not change when the resistor is moved).

So what should I replace it with? Leave it (value is correct), or 400 ohms per schematic, or 200 ohms(?) as installed?

As an aside, the cathode bypass capacitor, part 35, is listed as .05 in the schematic AND the parts list. But a 0.25mfd capacitor (a Philco part, 30-4446S) is installed, and looks all original - no signs of any servicing being done. So perhaps there have been some changes made to this radio?

Any advice would be appreciated.

Re: 37-620 Mystery Part - Value? - Chuck Schwark - 01-23-2011

Leave it alone, since a wire-wound resistor rarely will change in value.
That color code is for a 1/2W. 200 ohm part. If it is original to the set, then leave it.

Philco liked flexible resistors, but did not use them long in production.
See my site in the Parts Section for more info on the two physical types Philco used.
http://www.philcorepairbench.com/flexrest.htm

By the way, your Model 37-620 had many production and code version changes published.
One of the Production Changes addresses the resistor value discrepancy you found. 200 ohms is correct.


Chuck

Re: 37-620 Mystery Part - Value? - Ron Ramirez - 01-23-2011

As a Philco Phorum member, you have access to a free download which collects all Philco factory changes between 1933 and 1938 into one zipped PDF package. Look here:

http://www.philcoradio.com/phorum/showthread.php?tid=215

The file is "changes.zip".

Icon_smile

Re: 37-620 Mystery Part - Value? - davemc - 01-24-2011

Thanks for the tip on the CHANGES document!

How do you know what CODE (121,124 etc) and RUN number you have? There is no indication on the chassis or cabinet labels as to CODE. The serial number is S58653. On the FRONT of the chassis there are some ink stamps: 724 18 0(?). On the side is the letter "D". There is a pencil mark on the side of the chassis that MAY be a 3. But that's all I could find.

Based on the part parts numbers of the IF cans and filter caps, it appears I have a CODE 121. And the first change listed mentioning parts 34 and 35 I also appear to have. Part 35 is definitely 30-4446, .25mfd. Part 34 (the original question) is likely FADED VIOLET rather than RED (700 ohms not 200 ohms). That makes sense, since it measures about 800 ohms which is in tolerance and I can leave it alone (I like to keep things as original as possible). The change from 400 ohms (bakelite) to 700 ohms was apparently made at the same time part 35 was changed from .05 to .25mfd.

Thanks for the help!

Re: 37-620 Mystery Part - Value? - Chuck Schwark - 01-24-2011

The blue and white MODEL paper sticker on the inside of the cabinet usually has a CODE 121, 122, etc. on it.
If yours is intact, that's probably a Code 121, but Production Changes woudl still apply to the RUN you have.

You can figure it out by virtue of what changes in components you have matched to the run change in the notes.

Chuck