[Jeffhs]

"Recapping", i.e. replacing all paper/wax and filter capacitors, is the first step in restoring a vintage or antique radio to past glory. If you want to test the radio before starting the recap, use a Variac (variable voltage autotransformer) or a dim bulb tester. Start out with the Variac set at zero, then bring the voltage up by degrees, observing the chassis at the same time. Stop immediately and unplug the power if you notice smoke and/or sparks coming from the chassis; this indicates a short circuit which must be corrected before going further.

The dim-bulb tester may be used if you don't have a Variac. Connect a standard 100-watt light bulb in series with the radio's line cord, then plug it in. If the bulb lights normally, you can safely go ahead with further testing. However, if the bulb lights to full brilliance and then burns out with a bright white flash as soon as the radio is turned on (or, worse, as soon as the set is plugged in), there is a dangerous short somewhere in the chassis which must be cleared before anything else is done to the radio. Shorted filter capacitors and/or a shorted rectifier tube will cause excessive current drain, which will blow the house fuses or the line fuse in the radio because the caps and rectifier tube are in a position to short the power line directly to ground if defective.