At 02:58 PM 11/21/2014, drlegendre wrote: The 20 mA current interface was the standard current loop interface for Teletypes such as the ASR-33 sometimes used as consoles for DEC minis. I used them for a number of years on a couple of pdp8/m systems that had ASR-33s as consoles, and also took care of many 20 mA loops used with other Teletype models when I worked as an Associated Press technician in the early 1980s. AP used Lenkurt data sets to receive data from analog telco loops and convert it to current loops for teletypes. Dale H. Cook, GR / HP Collector, Roanoke/Lynchburg, VA http://plymouthcolony.net/starcity/radios/index.html