Autocorrelation preamplifier. Unit has seen extremely low use time. All controls switches board connectors cleaned corrected power supply per Phase Linear update, some IC sockets and best noise version op amp installed. Repaireds some RCA inputs and fortified them with glue. Replaced various capacitors anywhere in unit which measured off spec (about 20 caps changed). Install "star ground" modification to reduce noise and RFI ruggedize all board connectors auto corrector circuit. Spec of unit noise floor and channel matching is excellent! Tracks excellent +/-1db channel match!