08-25-2021, 02:34 PM
Yup, John, that's why many of the top level tube testers in the old days had an earphone jack to plug in a headset to test for microphonic tubes. You are right about the tube sockets being a potential cause, I have had it happen. A cold (bad) solder joint can also cause microphonic problems. This is why it is important to be sure of each solder joint we make as we repair these old radios.