This mic was purchased from infernalemachine (highly regarded mic seller on instagram) and not used since.

His description:

For sale a classic @sony C-37A serial number 3220 & CP-3 PSU serial number 1140, manufactured in 1961.

Heitaro Nakajima, an engineer working for Japan’s national broadcaster NHK, attended one research conference in Germany. There, he got to see and test the Neumann U47 and other mics made by Neumann, which at the time were unparalleled. 

Intrigued by the possibilities (and daunted by the prospect of buying a large number of expensive Neumann mics for NHK’s needs), he returned to Japan and began building a prototype condenser mic based on Neumann’s design principles but with some innovations of his own. Following some highly successful orchestral recording sessions, Mr. Nakajima told Sony about the prototype.

The C-37A was put into commercial production in Japan in 1955, the US release was in 1958, at an audio expo in Los Angeles. In my knowledge, there was no distribution in the EU back then. 

The C-37A is a tube LDC with an innovative mechanical control behind the capsule for polar pattern adjustment. The impedance circuit (cathode follower) inside the microphone is truly simple: a 6AU6 pentode tube (wired as a triode) and a few resistors. The mic’s output coupling capacitor and audio Fuji transformer are located in the PSU. The C-37A “C-3” capsule represents a milestone for Sony, in that it was their first capsule to use Dupont Mylar film. It is a single-diaphragm design, with a tuned, adjustable acoustic chamber behind the diaphragm. The ports on the chamber can be adjusted by the user, to switch between Unidirectional and Omnidirectional polar patterns.

I redo all the internal cabling inside, changed all the resistors with low noise 1% ones, cleaned the tube socket in an ultrasonic bath, cleaned the capsule, installed my favorite low noise 6AU6 tube.

I redo the cable coming from the mic to the PSU with Sommer Octave cable to the Sony 21-5P connector.

In the PSU, I changed all the electrolytic capacitors and I hollowed out the old can ones to hide the new ones.

As wonderful sounding as the classic Neumann & AKG mics from the same era.