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Silvertone Model 7104

This 1940 Silvertone is a farm radio, which means it was battery operated. It used a 1.5-volt A battery and a 90-volt B battery. It has inductive permeability tuning instead of the more common tuning capacitor. I made a battery eliminator power supply and mounted it in the battery compartment using an isolation transformer, some diodes, a LM317 regulator and filter caps. It is very sensitive and can be loud considering the maximum output is about a half watt. The knobs are not original. I made them from drawer pulls.

Notice the switch centered just below the dial. It is a battery saver feature. When switched on a resistor is inserted in both the B+ and the filament circuit to reduce the current draw. Someone a long time ago had bypassed the switch and apparently had made an AC operated supply. I replaced the switch and wired it back per the schematic. It works with my battery eliminator just fine. I was really surprised at the sensitivity of this radio. It picks up stations all across the dial with only a six-foot wire as an antenna.