When working with old tube based radios, transmitters, etc... the silver mica capacitors would sometimes experience migration of the silver, leading to breakdow

When working with old tube based radios, transmitters, etc... the silver mica capacitors would sometimes experience migration of the silver, leading to breakdown, generating a ton of "thunder clap" sounds in the audio output. I figured out a reasonable method to track them down, if you have the schematic, and a good DVM. 1 - Take out all of the tubes, except the high voltage rectifier, if possible (some systems wire them in series, in that case, this won't work) Be sure you have good and correct documentation about tube placement, you wouldn't want to make it worse. 2 - Measure the voltage across the resistor in series with said capacitors. You should read zero volts across them... even with 250 volts B+. If there is a voltage, you either have a resistive path to ground you didn't see, or a bad capacitor, leaking to ground. (There will be zero current through a good capacitor, thus zero volts across any resistor in series with it) 3 - Replace all the tubes This saved us hours of trouble once I figured this trick out.