I have a 1946 Convey AM radio. works quite well and it has an old phono jack and switch on the back. I thought it would be easy to simply replace the old jack with a new one. But it didn't work. I installed the new jack next to the original, and simply moved the wires from old jack to new jack. One wire in the original hookup was bare. I had to replace it, so I just used regular shielded wire.
Unfortunately the jack is dead. Has anyone done this? Found a solution? Any advice you can offer will be appreciated.
Is the switch part of the circuit?
Maybe a bad switch?
yup, good point
Two things about old tube radios. The phono input is of a different impedance value than what works for a guitar input jack to the active components. You may need to add a 68K ohm resistor from the positive jack lead heading into the circuit before it gets to the pre-amp for the phono input. Another reason why the jack is "dead" is a worn out tube, faulty or dried out capacitors/resistors in the signal path, etc.
Second, and most important, is that older tube radios can have lethal voltages running to the chassis.The super hetradyne circuits are much different than modern circuits.They have no transformer, so all that 120v ac power is going straight to the rectifier tube.
Even if you find a schematic online for the radio, there is a good chance the actual radio you have was not built exactly as the schematic. Parts during that era were scarce due to the war effort. Domestic manufacturers had to make due with what was available.
First, before trying anything, take a 100K ohm resistor and bleed all the capacitors to ground to remove any lethal voltage stored in the capacitors. Then replace the 2 prong plug and lead with a 3 prong. Connect the black + and white - to the original spots taken by the 2 prong setup. Then attach the green ground wire to the chassis. This way, if there are any lethal voltages leaking to the chassis, you will be able to tell us if the rest of the project was a success (meaning, you're alive to tell the tale).