Zenith b511b

[wa2ise]

Originally Posted by peverett

This set uses the small ones that are prone to the silver mica corrosion.

The cure is to carefully take them apart. Then remove the old caps and replace them with new ones of 100pf or so. It is a tedious process, but the radio will play fine once this is finished.

This problem is due to the manufacturer placing two caps on the same mica wafer. silver can migrate from one cap to the other, creating a leakage path. If the wafer is easily gotten to, just scraping the surface of the mica between the two caps will interrupt this leakage path, thus solving the problem. However, many IF transformers have this cap wafer buried under plastic pressure plates, and it becomes a bigger PITA to get at it. If you have to drill out a big rivet to gain access, at this point I'd use the 100pF mica caps as replacements. See halfway down http://www.geocities.com/wa2ise/radios/repair.htm for more info.

About 80% of old radios like yours won't have this problem.

As for the filter cap, it looks like the better grade of cap (electrolytic with a metal can, with cardboard over the can). It may still be good. The cheaper grade of filter caps often used in radios were just the electrolytic cap inside a cardboard "can". Those are always bad, as the cardboard lets the water in the electrolyte dry out. If you don't hear a lot hum when you try the radio, it should be okay.

A source of suitable caps could be had by taking apart something that used a switching power supply, like TV sets, DVD players, newer VCRs and computer power supplies.