I was trained on 15s, but I doubt I worked on a dozen. The old timers jumped on them. Models 28, 33, 35, 37, 40, 43, 4540 and ALL their attendant systems, 8 to 5 dataspeed converters and ALL data from vacuum tubes to digital. Finished out my career with a decade of cable splicing.
I loved working on those 28s though. They were my bread and butter. Here’s one woking at only 60 speed
http://www.youtube.com/watch?v=8bmnyOTqj3g
“I was trained on 15s,”
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While I was in the two-way radio business, RTTY was only a
ham radio adventure around 1965-1972. I had a few DX contacts from around the world, using my model 19.
I also remember a portable tty machine that I got through Army MARS, but do not remember the make or model.
I had no training on tty, much less any professional or business with them.
I also remember teletype art being popular. The most famous was the nude girl sitting on a stool. While I had a perf unit and tape reader, I never got into the art gig.