I'm hoping that someone might have a copy of the Brüel & Kjær 2801 Microphone Power Supply schematics.
I put together the 2801 microphone power supply, the 2615 cathode follower microphone pre-amplifier, and the 4134 microphone for a test.
I'm measuring 14.5v of DC after the internal 4uF blocking capacitor at the direct output. I measure 62v of DC before the blocking capacitor (signal path from the microphone).
When I speak from a distance into the microphone, I do get between 0-10mV of AC at the output.