...these are Field Effect Transistors which perform the equivalent of a tube...
I wouldn't subscribe that a FET does perform like a tube.
When FETs originally were introduced, this statement was often heard from those who found it was easier (and cheaper) to build a circuit using a FET instead of a tube.
There are some similarities, but there are even great differences.
E.g.:
- Most tubes are much more linear and the transition to the nonlinear range is softer.
- A tube works with and can handle much higher voltages (up to several hundred volts on common types). If used with high supply voltages, they have a greater dynamic range.
Tubes can even stand much higher voltages without breaking - in fact you almost never will find a tube that failed due to overvoltage at the input. This means you don't need to take care for that in a mic.
For a FET it's deadly coming in contact with the polarisation voltage.
- Most important for us: tubes do sound different to FET's, as a result of all the differences in their characteristics plus the necessary differences in mic design.
- Tubes give a nice heating to the mic, which helps to keep the capsule dry.
Regards
Kai