The AWA Museum recently received a donation of "Blue Lightning", a
replica of a 1910, 1/2 KW, Synchronous Rotary Spark Gap
Transmitter. It had been built by N4GG, in memory of his father,
2NJ.
This is not "OT", as can be seen in the next picture

The motor driving the rotary spark gap is a "standard of the
industry" unit:

have fun,
Duncan
K2OEQ