10-04-2017, 11:12 AM
This radio uses only one .01 uf line filter cap from the power switch to ground. I put a polarized plug on the chassis, with the hot side going through the switch, so only the hot side is connected to the line filter cap. There isn't a filter on the neutral side. Because the plug is polarized, I can't try reversing the plug to see if that makes a difference.
By the way, the filter is now a new safety cap. It is definitely not open.
Similar Philcos put a .01 filter on each side of the line to ground. If I put a second .01 safety cap from the neutral to ground, could that make a difference, especially if the hot and neutral in the socket are reversed? I've tried this on my workbench using test leads, and it makes no difference whatsoever, but I don't have any modulation hum here. There is an easy spot to mount a cap from neutral to a good ground nearby.
The reason I keep coming back to this is that Marcus and Levy stress the line filter(s) as a cause of modulation hum.
Next time I go to the customer's house, I'll take a 41-255 for comparison and a socket tester.
By the way, the filter is now a new safety cap. It is definitely not open.
Similar Philcos put a .01 filter on each side of the line to ground. If I put a second .01 safety cap from the neutral to ground, could that make a difference, especially if the hot and neutral in the socket are reversed? I've tried this on my workbench using test leads, and it makes no difference whatsoever, but I don't have any modulation hum here. There is an easy spot to mount a cap from neutral to a good ground nearby.
The reason I keep coming back to this is that Marcus and Levy stress the line filter(s) as a cause of modulation hum.
Next time I go to the customer's house, I'll take a 41-255 for comparison and a socket tester.
John Honeycutt
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