Folks, after a hint I have been able to find a page where it describes two of the boards as the ones of a KR50 keyer. http://www.k9rei.com/2016/05/30/restoring-a-ten-tec-kr50-morse-code-keyer/ The PDF on the page includes schematics and wiring information, so I am all set. Thanks to Chris K9REI for such a wonderful resource. jon, ea2sn / ae2sn