Excellent article on transmitter power supplies.
While my father Art Nott assisted in the construction of the first WKY in Oklahoma City as a teenager, here is another application of transmitter power supplies. At age 18 in 1925, he went to work for Oklahoma Gas & Electric Co., which had its headquarters in downtown Okie City. They communicated with several power plants via CW (Morse code), and he was an operator.
I don’t know how much power they used, nor the frequency; but for the transmitter high-voltage DC, they used a synchronous rectifier. This consisted of a synchronous motor driving a disk about 6 inches in diameter.
Half of the disk was conductive copper and the other half hard black plastic insulation. A pair of brushes made contact with the disk as it rotated to close the circuit on only the positive half waves of AC from a transformer.
He said that on transmitter startup, you turned on the switch to the sync motor and watched the plate voltmeter. If it went upward, you were OK; but if it went down you quickly turned off the switch and then turned it back on. Sometimes it took several times, but eventually the meter would indicate upward.
The transmitter worked fine; but for reception, streetcar QRM was a problem. The roller in the trolley pole made a good spark gap transmitter, which sometimes completely blanked the receiver. They had to operate fast between streetcars.