Hi Michael
I find these power supplies for these microphones to be less than par for a
top shelf microphone. They work for the mic and circuit they were designed for.
The capacitors are not quite the same standard as the Nichicon, Panasonic, Rubycon and Elna counter parts.
The quality of wire that is used in these supplies are average and not the best for a high end microphone.
I find that re-building the power supply with good capacitors, Teflon Silver coated Copper stranded wire makes a big difference in the performance of the microphone. Increasing the values of these components and adding by-pass capacitors decreases the ripple in the current and allows transients to flow quickly through the capacitor and the capacitor recovery time is less.
In custom builds I have also changed the transformer out with a Hammond and used high end Mills wirewound resistors for additional noise reduction. The power supply was dead quiet and the mic sounded amazing.
Reducing the voltage in the power supply does not necessarily result in a starved plate design. The 12xx7 tube variety can handle a wide range of voltages from more than 300vdc max to 45vdc on the lower end with out being a "starved plate." The typical C12 type circuit has any where from 55 to 75vdc and that depends on the bias scheme. I typically reduce the B+ voltage from 140 to around 120vdc to the mic. I have not heard of anyone reducing the plate voltage to where it is indeed starved.
I also modify the power supply to provide negative bias to the grid. This makes the mic a true fixed bias microphone. This gives the mic a much richer tone.
The bottom line is:
Everything matters