The C-38B is the FET version of the Sony C-37A microphone (in fact the original C-38 is the world’s first FET microphone) and uses the same 1.3 inch, 6-micron Mylar capsule. A unique feature of the capsule is the steel mechanical shutter located behind the capsule that changes the polar pattern depending on if the port is open (cardioid) or closed (omnidirectional) There is a small, recessed access hole for a screw that operates the shutter (see second picture).

The C-38B has low sensitivity and can handle high SPL with ease which makes it great as a close mic on drums (Ken Scott famously uses one on snare) or any loud source.