I have a Zenith table radio. Model I believe is a C756c. It will not power up and I suspect the selenium rectifier. Is is possible to build one to replace the defective one, and is the old one testable? I understand there was a long term endurance problem with these rectifiers. Please help, its a nice radio. Herman

Hi, Herman. Are you getting AC to the rectifier input, but no DC out? If so, then I'd conclude that the rectifer is shot.

You could replace with 1N4007 diodes.

:Hi, Herman. Are you getting AC to the rectifier input, but no DC out? If so, then I'd conclude that the rectifer is shot.
:
:You could replace with 1N4007 diodes.

: Doug, AC in and DC out. My analog meter shows somewhere around 150 dc. I did the test with negative lead on the chassis. Seems like alot but I really don't know.

Thanks

Herman, sounds to me like the rectifier is working. What are you seeing or not seeing that makes you think that there is no power? Do the tubes light up? If not, have you checked to see if one is burned out, causing the whole string to go out?

Is this an AC/DC set? I couldn't find any reference to the Zenith model no. you listed.

:Herman, sounds to me like the rectifier is working. What are you seeing or not seeing that makes you think that there is no power? Do the tubes light up? If not, have you checked to see if one is burned out, causing the whole string to go out?
:
:Is this an AC/DC set? I couldn't find any reference to the Zenith model no. you listed.

:Doug, I did some further investigation. I found a 39 Ohm resistor shorted between a 12au6 and 12ba6. Both I guess are RF Remote cutoff pentodes. I'm not sure where to get a 39 Ohm resistor (orange, white, black, and silver). Would this be a 35 watt resistor? Ceramic? Looks like a common one to me. Tube shaped and about 3/16 by 1 1/8. The label on the radio says 35 watts. I did find a chassis number of 7c06. Maybe this will help identify this rig. I don't have a schematic or specs. Just shootin in the dark as a layman. Any thoughts?

Herman

Herman, you should be able to find a schematic under "Resources" in this website. Many tube radios take 35W, or so, total, so a 35-W resistor would be out of place.

I fear that you've bitten off a little more than you can chew, at least for now. If you're just starting out, I'd recommend starting with a simpler set, an AC/DC 5-tube, post-war reciever. There are several basic books on antique radio repair and electronics that would be good to study - you can search on Google or Amazon.

:Herman, you should be able to find a schematic under "Resources" in this website. Many tube radios take 35W, or so, total, so a 35-W resistor would be out of place.
:
:I fear that you've bitten off a little more than you can chew, at least for now. If you're just starting out, I'd recommend starting with a simpler set, an AC/DC 5-tube, post-war reciever. There are several basic books on antique radio repair and electronics that would be good to study - you can search on Google or Amazon.

::Herman, you should be able to find a schematic under "Resources" in this website. Many tube radios take 35W, or so, total, so a 35-W resistor would be out of place.
::
::I fear that you've bitten off a little more than you can chew, at least for now. If you're just starting out, I'd recommend starting with a simpler set, an AC/DC 5-tube, post-war reciever. There are several basic books on antique radio repair and electronics that would be good to study - you can search on Google or Amazon.

Thanks Doug, I did finally find a schematic. You are correct in the resistor value. This rig takes a 39 Ohm, 1 watt, wire wound. I think I'll give that a try then move on to something else. Thanks for all your suggestions and advice.

73
Herm