03-11-2011, 04:41 PM
I was looking at my schematics for this RCA 56x5 and Philco 42-327. The Philco hummed loudly after I had replaced all the caps, filters included. I was looking at the schematic and a question occurred:
If the filters are bad and not filtering, a steady (or near steady) current is sent to the primary coil of the speaker's transformer, thus, causing the speaker to get a steady signal and hum. Looking at the diagrams it appears that the current would come straight from the wall, no step down, no filter, no half-wave rectifier. Just straight AC. Am I right to assume that if there is a hum and it is the filter caps that the radio would have no volume control, the tone would be steady, and the reading at the output of the speaker would be proportional to the turn-ratio for primary-secondary windings?
It was mentioned in another post that the 50L6 tube (Beam Power Amp) which feeds to the speaker transformer could cause a problem with loud humming if the internals were shorted. A resistance check on a broken 50L6 should then show a short for two pins... excluding the heater element, of course, right?
Ron, and all, I think I'm actually beginning to figure the components out, how they work, that sort of thing. Please, though, tell me if my logic is incorrect.
Thanks!
-Brandon
If the filters are bad and not filtering, a steady (or near steady) current is sent to the primary coil of the speaker's transformer, thus, causing the speaker to get a steady signal and hum. Looking at the diagrams it appears that the current would come straight from the wall, no step down, no filter, no half-wave rectifier. Just straight AC. Am I right to assume that if there is a hum and it is the filter caps that the radio would have no volume control, the tone would be steady, and the reading at the output of the speaker would be proportional to the turn-ratio for primary-secondary windings?
It was mentioned in another post that the 50L6 tube (Beam Power Amp) which feeds to the speaker transformer could cause a problem with loud humming if the internals were shorted. A resistance check on a broken 50L6 should then show a short for two pins... excluding the heater element, of course, right?
Ron, and all, I think I'm actually beginning to figure the components out, how they work, that sort of thing. Please, though, tell me if my logic is incorrect.
Thanks!
-Brandon
