Wiring silicon diode and resistor

[jln1966]

I am working on a 1959 Zenith table radio. I am replacing the selenium rectifier with a diode and resistor. What is the proper way to wire them in? Are the resistor and diode wired id series? How do you tell which end of the diode is + and -? Also there is a .047 bumblebee cap connected from the + side of the rectifier to the chassis. Is the cap required with the diode or can it be eliminated?
Thanks,John

[Tom Bavis]

Model number? I may have the schematic if you don't. The selenium rectifier is usually marked (+) or red on the cathode terminal. This is banded end of the silicon diode. Yhis is the rectifier output to the filter caps. A 39-100 Ohm 2 watt resistor in series will drop about 4-10V, and provide a little surge limiting. If there's a resistor already, you can increase it (but I'd leave it myself...). The bumblebee capacitor is leaky - trust me! Replace it with a .01 or .015 uF 'Y' capacitor. 'Y' capacitors are designed and safety tested for line-to-ground connection. Modern equipment MUST use these to get safety agency (UL, CSA, etc.) approval. .015 is the largest value that would meet the ground leakage current limit (0.7 mA maximum).

[jln1966]

The chassis # is 7c06 The model # is missing from the label on the bottom. I got an orange drop to of the same rating to replace the bumblebee. Will that work? One tube was bad also. I have a used one to replace it.
Thanks,John

[Tom Bavis]

That chassis number is in Sams 478-19. I may have it - I'll look. I would get a Y-capacitor to replace that one, as it's critical for safety. The AC power line can get surges of up to 2000V during lightning storms, and I wouldn't trust a 600V cap there. If you're replacing it, use the best replacement part.

[jln1966]

I got the radio recaped and put the diode and resistor in. I fired it up and the tubes all glow but there is no sound or static at all. It does have a very slight hum if I put my ear up to the speaker. The resistor gets very real fast,hotter than the tubes. Is this normal? What would cause the no sound?
John

[Tom Bavis]

If it gets REALLY hot, you may have a short on the B+. Electrolytic cap is the most likely suspect. I DO have that schematic - email tbavis(at)rochester(dot)rr(dot)com