AKG thought it was worth installing the tube upside down in the ELA M-251 to shorten the capsule wire and associated capacitance.

Here's a VERY short circuit from capsule to impedance converter (FET).

So here’s the circuit inside the head basket:

The parts identifiers refer to the original MXL part labels on the circuit board. The 1 G resistor comes from MXL. The other two resistors are new. The new FET is a type J305 for lower input capacitance. Backplate bias comes from the hot end of C12.

All the parts associated with the input stage are removed from the PCB except R7. The input capacitor, the two 1G resistors R1 and R9, the FET, R6, R13, and R14.

While I’m in here, I changed C3 and C4 to 1uF, bypassed the electrolytics, and changed D3 to a 12V zener.

Front view and Side view. The most important upgrade - an RK-12 capsule from Microphone-Parts.com

Inside view.

The switch.

Cardioid or Omni.

Shiny bits.

The mic with its pants on.