Warning. Vintage Radios operate at lethal voltages. Take extreme care when working on live chassis.
If you aren't sure about what you are doing then don't touch!
Checking Filter Condensers
A handy tool consisting of an electrolytic condenser with a lead and test prod soldered to each terminal will enable filter condensers to be readily checked. To use the tool , simply turn on the set and apply positive and negative leads to the corresponding terminals of the condenser in question. The output of the set will improve if the filter capacitor is defective.
Checking Converter Operation
Connect a voltmeter of suitable range between the B plus connection of the oscillator coil and chassis, i.e., across the bypass condensor, and short circuit the oscillator section of the gang condenser to chassis. A reduced reading on the voltmeter indicates that the oscillator section is working.
The reason for the reduced reading is that bias across the oscillator grid leak is removed by shorting the gang. This in turn causes the triode section to draw more current, thus resulting in a greater voltage drop across the oscillator plate dropping resistor
Frequently in circuits where persistent oscillation occurs and which cannot be traced to any circuit fault, it is possible that the various coil shields etc, are not as effective as they should be.
Where this fault is suspected, it is well worth the time and effort to remove these shields and tighten the rivets holding the spade lugs, which are used to hold the can to the chassis.