My RCA R-100 phono attachment has what I would say is more "motor hum" than it should. It looks like there are two capacitors, one on each side of the motor, wrapped around the side, and then wired in with the on/off, volume switch. I cannot seem to see the values on these from the schematic. Does any one know if those are the cause of the hum? It is not an audio hum thru the amp when connected, it is only coming from the motor, which I have oiled, etc. Also, there is no change in volume with the volume control on the phono, only with the volume on the radio it gets connected to. Any suggestions are appreciated.

Those 2 caps are part of the tone shaping network for the cartridge. They probably are not your cause of hum (RCA even suggests you change them to get the tone you want). Here's the schematic from this site if you want to replace them anyway....http://www.nostalgiaair.org/resources/680/M0015680.htm
Did you replace your cartridge? They were crystal, and there's a 100% chance it is bad. There are many other causes of hum, such as what type of input/amp you are using to play it though.

:Those 2 caps are part of the tone shaping network for the cartridge. They probably are not your cause of hum (RCA even suggests you change them to get the tone you want). Here's the schematic from this site if you want to replace them anyway....http://www.nostalgiaair.org/resources/680/M0015680.htm
:Did you replace your cartridge? They were crystal, and there's a 100% chance it is bad. There are many other causes of hum, such as what type of input/amp you are using to play it though.
:
I have a replacement high output cartridge that works fine. The hum is definitely the motor, not the audio circuit. I may replace them anyway, can you suggest whether or not they should be polarized, and values? The schematic does not seem to indicate.

Thanks,

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SUCK MY DICK YOU OLD GEEZERS

A couple of possiblities:
(1) Does the motor use a starting capacitor? If so, if this cap weakens, the motor will either not turn at all without a "helping hand" or will be underspeed with a hum. If the motor starts by itself OK and spins at the correct speed (or has no cap wired into the motor circuit), this isn't your problem.
(2) most motors were fastened to the turntable assembly using three very soft (live-rubber) grommets or bushings. These were mainly intended to dampen the sound of the motor rotating vibration from the turntable/case but also decoupled the AC hum acoustic component as well. After 50-60 years, these grommets become rock-hard and become near-perfect sound conductors instead of isolators. The turntable effectively becomes a "sounding board" in this case.

From what I've seen on the 'net, this platter was not self starting, and has to be 'spun' to start, much like the first electric clocks that needed a 'spin' start...Is this the case here?

:From what I've seen on the 'net, this platter was not self starting, and has to be 'spun' to start, much like the first electric clocks that needed a 'spin' start...Is this the case here?
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I have no idea- but if so, that is an incredibly poor design for a consumer product!

My guess is that the motor has a starting cap embedded in it that has "gone south".

::From what I've seen on the 'net, this platter was not self starting, and has to be 'spun' to start, much like the first electric clocks that needed a 'spin' start...Is this the case here?
::
:I have no idea- but if so, that is an incredibly poor design for a consumer product!
:
:My guess is that the motor has a starting cap embedded in it that has "gone south".
:
According to the schematic, it requires a push, and the schematic indicates minor motor hum is normal. Maybe it is just the way it is.

Yes, a quick search of Google confirms the quirks of this model. Seems like it has "features" that one would expect of a 1919 electric phonograph, not one from just before WW2. What was RCA thinking?

Supposedly this unit has a synchronous motor that will run just as well backwards as forwards, depending on which direction you spin it to start. What a great feature for a phonograph (NOT!).