[GreenKeys] Inside a REC-30 rectifier

[Jim Haynes]

Teletype preferred to use constant voltage transformer power supplies, but
those require the power frequency to be pretty accurate.  For military and
other uses where the power frequency is not likely to be accurate they 
used thyratron regulated power supplies.  Later they used magnetic 
amplifier regulated power supplies.

Calling it a switching regulator power supply is I guess technically
accurate; but modern switching regulator supplies do their switching at
much higher frequencies than the power line frequency.  Hence the magnetic
components can be much smaller and lighter since so much less inductance
is needed.  So it's not that Teletype engineers didn't get the message;
rather they had to work with what was available at the time, which did
not include high speed switching transistors.