What is a microphonic tube?
If a tube is “microphonic” it will “howl,” or feedback, like a microphone. No tube is free of microphonics, and some say that a little is actually wanted for a livelier sound. Microphonics are caused when the insides of a tube start to loose their solid construction from vibration. There is no fixing this. All we can hope for is that our tubes are well constructed. (technical explanation of microphonics) If a tube rings like a telephone it suffers from “filament rattle.” Like a microphonic tube it should be replaced. Filament rattle isn’t technically the same since the tube isn’t acting like a microphone. Often you’ll hear people mistakenly identify filament rattle as microphonics. It’s well known that you can tap on tubes to hear if they’re microphonic or suffer from filament rattle, but BE GENTLE. You can damage the tube when it’s hot. Also, don’t use your finger! If you hear the tapping being amplified don’t freak out, as said before all tubes are microphonic. Tapping should be rese