Zenith M730 Part II

Well it's done. I got all the caps replaced. I was not able to re-stuff the old multi section cap and ended up putting the new caps under the chassis. Here is a pic with all the new caps. The orange pillow shaped ones and the large striped cans. I forgot to take a picture of the replacement for the selenium rectifier, but you can see most of it in the lower right corner. I installed 2 33ohm 10 amp resistors (in series) in front of the 1n4007 diode to lowr it's voltage output to 130vdc about 5 volts lower than it should be but that is within tolerance.

The only issue with the radio after I finished recapping is that I accidentally hooked the AM loop antenna to the FM antenna connector and Vice-Versa. once that was corrected it works just fine, no re-alignment needed.

Cleaned and lubed all pots and bearings.
Cleaned the FM/AFC/AM switch.
Cleaned most of the Cadmium Sulphide off the chassis.
Cleaned the dust and spider webs out of the case.

Implemented the following safeties:
recapped (of course).
replaced selenium rectifier with a silicon diode.
larger surge resistors
polarized plug
rear interlock keyed for the polarized plug.

1 tube tested bad on my tester but I am debating whether to replace it at this time.


Anthony Selvaggio said...

i am putting 2 33ohm 5 watt in front of the 1n4007 diode will this be ok?

Flinx said...

It is not really necessary to put a voltage dropping resistor unless the voltage is really high. There is already a 22 ohm resistor there and if the voltage is within 10 volts plus or minus of 140vac on the plus side of the diode, that is ok.

Anthony Selvaggio said...

putting your Zenith M730 on line really helped me . I too found one bad tube but here is how it went....it was a 6t8 tube i replaced it with a new tube and then the radio would not work. then i looked up what tube should be there,it a 14gt8 now it works, i know shame on me for not looking at the schematic first.