Collins 651S1 Receiver

The Collins 651S-1 began its production life in the Fall of 1970. The receiver is a ruggedized, completely solid state, triple-conversion, superhetrodyne design with base support of 255kHz to 29.9999 Mhz (297,500 channels) plus remote control capabilities. There is a variable BFO feature that does provide 10Hz SSB and 150Hz CW fine tuning control sans digital display visual feedback. The standard model supports AM, SSB and CW modes with 16kHz, 6kHz and 2.7kHz filters. This receiver is devoid of modern day ham radio receiver features like notch filers, noise limiters/blankers, RIT/XIT, pass-band tuning etc.

The 6 digital display deployed pre-Nixie/LED, blue-green color, Vacuum Florescent Display (VFD) tubes (TUN-SOL DT1704C). All digital technology was implemented with descrete logic gates and shift registers - no MPUs or magic controller anythings in those days. The maintenance manual is quite thick due this earl;y digital technology. The Principles of Operations manual is a good time-machine tour for those so technically inclined. The calibration process in the Maintenance Manual far exceeds the complexity of anything I have ever seen.

I've heard original cost figures ranging from $10-30k depending on options. The primary customers were U.S.Coast Guard, Air Force and other U.S. Government organizations. Given the price, I don't believe any ads were placed in QST.

Options

VLF - An option was available to extend the frequency range down to 12kHz, perhaps to monitor submarine fleet encrypted RTTY signals. This was a small board attached to the shielded RF module.
Remote Control - a optional RS-232C/MIL-STD-188C computer interface was available to support the Collins 514S-1 Remote Control Unit or other computer-based systems. The U.S. Air Force used these on tactical weather systems.
Filters - 200Hz, 500Hz, 1.1kHz, 3kHz and 8Khz were optionally available.
ISB - An independent sideband unit was optionally available to support old school, encrypted duplex voice operations.
RTTY - A teletypewriter control unit (TCU) provides remote RTTY control with a Collins 514S-1 unit.
FM - Narrow-band FM was an optionally available with squelch.
SCAN - A frequency scan option was available.

For additional product information see the excellent Collins Collectors Association 651S-1 archive product materials and the Principles of Operation manual linked below.

Manuals

651S-1 Operation
651S-1 Principles of Operation
651S-1 Installation
651S-1 Maintenance
651S-1 Schematics
651S-1 Parts List
651S-1 Service Bulletins

Restoration Notes - as published in the Collins Signal magazine

I documented my restoration efforts in the following document.

651S-1 Restoration Notes