Just acquired these off EBay, a couple of CM-652 small diaphragm condenser mics. I blame Yeti and FreddyG for my new found affliction for vintage microphones. These old Calrecs require tuchel connectors, a modified XLR that screws on to the mic, and a wiring mod to use phantom power. Back in the 60s, these 600 series Calrecs had proprietary power supplies, and were unbalanced. They were often used for broadcasting radio/TV in Great Britain, and were used in abundance by the BBC.