The Rockwell Collins 851S-1 is a version of the HF-8050 with thumb wheel tuning and VBFO tuning if installed.  Like the HF-8050 it is triple conversion and 5 additional mechanical filters can be installed in the sister board attached to the Channel A-IF board.  Many other options are available as noted in the literature below.  A High Performance RF translator used in the HF-8054A (637-1767-003) can be substituted for the standard RF Translator (637-1767-001) with excellent results. Some 851S-1 receivers are not configured for ISB (independent side band).  Instead of having USB on the A IF board and LSB on the B IF board, these units had USB on the A IF board and the filter for LSB mounted on the attached sister board with no B IF board in the radio. 

Pictures above is the 851S-1 side by side with the only existing 851S-1A prototype.  The 851S-1A uses all the same internal cards except the control card along with a built in microprocessor and appropriate front panel.  Note the 851S-1 below on the left which has 10 HZ tuning while the 851S-2 on the right has 1HZ tuning.  Only seven 851S-2s were made.

851S-1 Brochures

Note the company brochures on the 851S-1:

 

851S-1 Data Sheet

Note the complete 851S-1 Data Sheet:

 

851S-1A and 451S-1 Receivers

The prototype 851S-1A (pictured at the top of the page) was a single production model and very rare. Several brochures were produced of this receiver along with another prototype receiver, the 451S-1 but neither were put into production.

Notes the brochures below: