The RS-38 microphone was also used with the GF-11/12 aircraft transmitters. John WA4WDL The RS-38/38A was the common PTT carbon unit during my Navy service in the '60s and also when I worked in Navy depot shops in the early '70s. A few years ago a fellow 'ABEN' in New Jersey was selling NIB Telephonics units but I think he lost everything in a fire. EdZ