I've been messing around with machine-generated Morse Code since about 1971 (on a Univac Solid State 90), but this set of pages is about a demonstration that I did at the Computer History Museum in 2015. The first computer I ever programmed was an IBM 1440 (A slightly modernized, cost-reduced version of the wildly popular IBM 1401). A good capsule summary of these two can be found at Ed Thelen's site based on the BRL, a "census" of computers published yearly in the 1950's and 1960s. That link apparently hits an anchor right about where the 1401 description ends, and the 1440 one begins.
One popular unofficial use of these machines was the generation of music on a nearby radio. The seventh harmonic of the machine cycle time (11.5 microseconds) was in the AM broadcast band, and it was easy to hold one of those new-fangled transistor radios near the machine, where variations in operations could modulate that "carrier" In an attempt to re-create that effect, the program described in explain_MMTEST was written. The demo itself is described (with annotated source code) in mhello.html