I have modified my pair Oktava MK-319s.
Basically, I took out plastik cap outside the sound capsule,
treated the inside of the mike case with Silicon RTV,
Changed BIAS and Leak resistors, gate cap and the FET.
Before:
and After
I recorded my classical guitar with it straight into my N72.
Excuse my playing I have not played classical guitar ages.
Here is the recording.