Microphonic Phase Inverter Tube?


Active member
Hey everyone,
I know what the signs are of a Microphonic Preamp tube in general are when they're in the sound stages (V1, V2, V3, V4, etc..). However, is it the same signs when a Phase Inverter goes microphonic? or should I watch for other signs?



Microphonic tubes all exhibit the same behavior - if you tap them, you hear it through the speaker. If the microphonics are bad enough, the amp can make "ringing noises" or go into full-scale oscillation, especially in combo amps, where the sound from the speaker can vibrate the tube.

The severity of microphonics is also a function of how much amplification occurs after the tube. The first preamp tube is usually the worst, because there is a lot more amplification following it than than other tubes later in the chain.

The phase inverter, normally being the last tube in the chain before the power tubes, is typically least affected by microphonics, so tubes that are unusable in the earlier preamp stages can typically be used in the phase inverter without problems.