08-27-2025, 09:10 PM
Hi Tim,
You can check the transformer by ohming between ground and the transformer side of cap #51 on the schematic. (Per the schematic, this is an "autotransformer", where the primary and secondary are actually the same winding.) You should get a reading. Then read between the 2 photocell terminals. You should get a lower reading. However, I don't know what those readings should be. I think that part of the reason for this transformer is impedance matching, and the other reason for the transformer is to filter out the high frequency AC driving the source.
Also verify that the needle does move and that somehow the needle / mirror mechanism has not frozen solid. However, I think that it is suspended in rubber so there should be some compliance.
One other thing. The phono preamp is used solely for the BOL pickup. It is not used by any other part of the radio. So it could be that the BOL is good but the preamp is bad. Try touching the same junction between the autotransformer and Cap#51 with a screwdriver while touching the shaft. This should inject a hum into the amp. If you do not hear a hum, try the other side of the cap. If no hum on either side, troubleshoot the preamp. If you hear a hum on only on the tube side of Cap 51, the transformer may be shorted. The preamp tube and the detector / 1st AF amp are both type 7C6 so you can swap them. In addition, Loctal sockets and tube pins are notorious for getting dirty and intermittent (I don't know why 7 and 9 pin miniature tubes don't have the same issue).
If you want to substitute another tonearm, hopefully the turntable was made for several years, but the BOL was made only for the 1941 and 1942 model years. Non-BOL arms from a similar Philco Turntable from 1940 or 1946 may fit. I would recommend against excessively hacking the BOL head to fit another cartridge, as it is rather rare.
I have not heard a BOL live, but there is one on you tub e. I'm sure that it is much cleaner than a crystal or ceramic cartridge and as good as a GE RPX or other magnetic cartridge of that period.
You can check the transformer by ohming between ground and the transformer side of cap #51 on the schematic. (Per the schematic, this is an "autotransformer", where the primary and secondary are actually the same winding.) You should get a reading. Then read between the 2 photocell terminals. You should get a lower reading. However, I don't know what those readings should be. I think that part of the reason for this transformer is impedance matching, and the other reason for the transformer is to filter out the high frequency AC driving the source.
Also verify that the needle does move and that somehow the needle / mirror mechanism has not frozen solid. However, I think that it is suspended in rubber so there should be some compliance.
One other thing. The phono preamp is used solely for the BOL pickup. It is not used by any other part of the radio. So it could be that the BOL is good but the preamp is bad. Try touching the same junction between the autotransformer and Cap#51 with a screwdriver while touching the shaft. This should inject a hum into the amp. If you do not hear a hum, try the other side of the cap. If no hum on either side, troubleshoot the preamp. If you hear a hum on only on the tube side of Cap 51, the transformer may be shorted. The preamp tube and the detector / 1st AF amp are both type 7C6 so you can swap them. In addition, Loctal sockets and tube pins are notorious for getting dirty and intermittent (I don't know why 7 and 9 pin miniature tubes don't have the same issue).
If you want to substitute another tonearm, hopefully the turntable was made for several years, but the BOL was made only for the 1941 and 1942 model years. Non-BOL arms from a similar Philco Turntable from 1940 or 1946 may fit. I would recommend against excessively hacking the BOL head to fit another cartridge, as it is rather rare.
I have not heard a BOL live, but there is one on you tub e. I'm sure that it is much cleaner than a crystal or ceramic cartridge and as good as a GE RPX or other magnetic cartridge of that period.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis
Best Regards,
MrFixr55
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