The "Lipstik" condenser microphone system

The details of construction of a miniature condenser microphone and the associated cathode-follower amplifier are given. Factors contributing to the inherent electrical noise level of the system are analyzed theoretically and experimentally. Relative qualities of various subminiature tubes for use in the "free grid" amplifier circuit are tabulated, and related to tube construction features. Microphone sensitivity, frequency response, polar patterns, and temperature coefficient are given.