I have this record player radio and the radio part works fine but barely any sound from the record player. I think the cartridge might be bad but how can I tell? Putting a screwdriver on the connections of the cartridge doesn't seem to drive any hum through. On the newer ones this trick would work but this older one seems not to test this way. This set is about a 1940.

:I have this record player radio and the radio part works fine but barely any sound from the record player. I think the cartridge might be bad but how can I tell? Putting a screwdriver on the connections of the cartridge doesn't seem to drive any hum through. On the newer ones this trick would work but this older one seems not to test this way. This set is about a 1940

First thing comes to mind is a dirty function switch, or if it has a mute switch check that too.

A model number will help. Zenith used the Cobra circuit, which may or may not hum, depending on whether the cartridge is plugged in or not. However, I'm not sure if they used the Cobra system as early as 1940. In 1940 they probably used a ceramic cartridge, which should be of a high enough impedance to hum if you touch the grid terminal (not the ground return terminal).

There could be a broken wire or a short or a bad selector switch, as was suggested before.

T.

John: Is it a cobra model, which will be aparent by the beady little eyes on the snake-like tone arm? I worked on one of these for a friend and it doesn't seem like much could go wrong with the cartridge. As I seem to recall, it is a variable capacitor rather than a ceramic, crystal, or magnetic pickup. You can find a lot of info about this system on the internet.
Mark from Kalamazoo

:John: Is it a cobra model, which will be aparent by the beady little eyes on the snake-like tone arm? I worked on one of these for a friend and it doesn't seem like much could go wrong with the cartridge. As I seem to recall, it is a variable capacitor rather than a ceramic, crystal, or magnetic pickup. You can find a lot of info about this system on the internet.
:Mark from Kalamazoo

If you do need a cartridge for it. You can get a new one at Garage-A-Records.com The old Zenith part number is 142-74 .. <> Warren <>

::John: Is it a cobra model, which will be aparent by the beady little eyes on the snake-like tone arm? I worked on one of these for a friend and it doesn't seem like much could go wrong with the cartridge. As I seem to recall, it is a variable capacitor rather than a ceramic, crystal, or magnetic pickup. You can find a lot of info about this system on the internet.
::Mark from Kalamazoo
:
:If you do need a cartridge for it. You can get a new
one at Garage-A-Records.com The old Zenith part number is 142-74 .. <> Warren <>

Thanks. It's not a Cobra. I think it is a Model 68683 or is it 6S683? I tried cleaning the switch and no difference so I hooked up a newer style cartridge and got moderate sound so think it is the cartridge.

Make sure that capacitors aren't leaky, and that resistors aren't drifted. Sometimes the signal is sent through a resistor-capacitor network for tone correction. Aged components can ruin performance. A leaky capacitor, as far as a crystal cartridge is concerned, is leaky in the millions of ohms. When you connect a capacitor to your ohmmeter (set to its most sensitive setting), if the needle jumps up at all, it must fall back to exactly where it came from for optimum performance. If it lingers at all, then the capacitor has leakage.

A model number will be helpful.

T.

:Make sure that capacitors aren't leaky, and that resistors aren't drifted. Sometimes the signal is sent through a resistor-capacitor network for tone correction. Aged components can ruin performance. A leaky capacitor, as far as a crystal cartridge is concerned, is leaky in the millions of ohms. When you connect a capacitor to your ohmmeter (set to its most sensitive setting), if the needle jumps up at all, it must fall back to exactly where it came from for optimum performance. If it lingers at all, then the capacitor has leakage.
:
:A model number will be helpful.
:
:T.

Hard to read it but I think it says 6R583 and parts seem to agree with the schematic.

If R5 is drifted, that can significantly reduce volume. I'm not sure why R4 is there....perhaps to reduce bass. You can try increasing its value or try omitting it all together. That will increase volume, as well as bass. If you want to decrease bass without parasitic resistor R4, you can try reducing the value of C4 as low as .001 MFD. Reduce to suit your taste.

If C4 is open, that will, of course, reduce volume.

T.

:If R5 is drifted, that can significantly reduce volume. I'm not sure why R4 is there....perhaps to reduce bass. You can try increasing its value or try omitting it all together. That will increase volume, as well as bass. If you want to decrease bass without parasitic resistor R4, you can try reducing the value of C4 as low as .001 MFD. Reduce to suit your taste.
:
:If C4 is open, that will, of course, reduce volume.

Thanks, have tried those components and no luck. still has low volume that doesn't change with the volume control but can't find anything wrong. Must be the cartridge.
:
:T.

If the radio works fine (volume control, too), then that eliminates the volume control as a culprit. However you say that the phonograph output is low, and is unaffected by the volume control. That leads me to believe that it isn't even going through the volume control. Either there is a fairly big short in the cartridge circuit, or there is an open (broken wire, open capacitor, open resistor, etc.). Check all of this very well. Trace it back. Sometimes an audio source (cartridge, radio circuitry, etc.) can put out enough of a signal to radiate via capacitance, and still get into the amplifier, even though it isn't going through its normal path. Trace your wiring back from the volume control until you can no longer feed a hum into the amplifier with your finger or a screw driver. You don't get hum in the tone arm wiring. That indicates an open (or possibly a short) somewhere.

T.