Resistors insulated 1940

[HiFiCanada]

I have this 1940 Delco radio, the resistors look a lot like wire wound resistors, at first, thats what I thought they were. In the schematic for this radio it is called a insulated resistor. How good are those, why did Delco use this type of resistor instead of the regular carbon composite type? Is it because of shielding out more interference?
Should they need to all be replaced?

[Electronic M]

Those look like regular old school "dog bone" resistors to me. If they test good I'd leave them be. To read the value use the standard resistor code and read them "BED" Body-End-Dot.

[HiFiCanada]

Well, I got the original service manual and schematic, most of the resistors are out by 30-50 percent, I guess there is no choice but to replace them.

[Reece]

If you need to determine what wattage these "dog bones" are, here are some pictures that help:

http://www.philcorepairbench.com/resistcompare.htm

[HiFiCanada]

I found this chart really helps me in learning how to read the dog bone resistor values, double checking that with the schematics. So far everything checks out as the proper values.
http://www.nostalgiaair.org/Referenc...s/reschart.htm

[HiFiCanada]

Originally Posted by Reece

If you need to determine what wattage these "dog bones" are, here are some pictures that help:

http://www.philcorepairbench.com/resistcompare.htm

GE L-660 radio
Found one resistor that is a one watt resistor, higher wattage then what it says in the schematic and parts list. Not sure if it was replaced a long time ago, or updated in the later production runs?
Found another dog bone resistor approx 2 in long x 3/8 dia, and the schematic lists that as a one watt, which can't be. That one measured right to spec, so I kept it there. Most other 1/2 watt resistors were replaced with one or two watt, full body resistors just to be safe.
Not sure if the schematics and parts list are always accurate.

[Reece]

It's OK to use a resistor with higher wattage than spec, just not lower wattage. The manufacturer may have run out of the lower rated ones on that run.

As to "insulated resistors," notice that the kind we are more used to from the 1940's on don't have their resistance element exposed but have a cylindrical case on which are the color bands of the code. The old dog bones with the wire wrapped lead on each end were just chunks of resistance rod painted, thus not really "insulated." I suspect that's where the term came from.

[HiFiCanada]

Thanks for the info on resistors Reece and Electronic M, this gave me more confidence and knowlege in replacing the dog bone resistors. I finally understand the color code and how it works "Body-End-Dot.
I think that there was only three colors at that time, so it is a good way to start learning color codes with the dogbone resistor, much easier to understand
I verified that I had it right when replacing resistors, by the color code, the schematic and parts list for the old radio and the Ohm meter checking the values of the resistors, just to make sure I have everything right before I replace. A 60 year old newbie has got to be very careful, now with hands on experence, it is really starting to sink in. Now I got the radio recapped and wired in new resistors, one radio is already playing the tunes for over a few hours now.