On 11/07/2016 10:59 AM, ethan at 757.org
ran off 415 Hz 3-phase power. The mid-sized
ones had the motor-generator set built into the back of
the machine. The 415 Hz (regulated) power was
transformed to low voltage and run through an
inductor-input filter and then series pass regulated.
They had a circuit they called an "electronic capacitor"
that pulled extra current through the inductor during the
voltage peaks, so the inductor carried enough current
during the voltage valleys. This reduced the ripple
current on the capacitor banks.
The 360s ran off single-phase 120 V 2500 Hz power,
produced by a "converter-inverter" unit in the back, that
converted utility 3-phase power to DC, then inverted it
with an SCR inverter. This made the DC power supplies in
the machine quite small. Since they ran off regulated
2500 Hz power, they dropped only a very small voltage
across the series-pass transistor.
Am I getting this right?
So they take AC turn it to DC then turn it back to high
frequency AC then turn it back to DC to drop the need for
larger capacitors to keep the DC clean?
Yes, that's how the 360's (at least mid-range) were set up.
You could tell, the converter-inverter was INSANELY loud, at
a massively piercing audio frequency. The key was that this
one unit gave regulated AC power to all critical power
supplies in the system, so they could skimp on regulation on
the individual power supplies.
It actually didn't work so well, if you had crummy power,
which we had a bad case on at Washington University in the
70's - 80's. They had 4160 V cables buried all over campus,
fed from one transformer at the power plant. These cables
were in concrete "conduits" which had water leaks. So the
wires, with 4160 V on them, were essentially sitting in
muddy water all the time, and corona discharges broke down
the insulation. We had one of these cables fail every
couple months, with a massive power dip for a few seconds
before the fuses cleared. But, for weeks before the big
POP, they would be arcing and flashing, which drove the 360
crazy. A small dip would cause things like control store
parity errors, main store parity errors or just system
power-on resets. They got a Dranetz analyzer, and could
correlate more than half the machine crashes with a power
glitch. They got some big Digital Power Systems
ultra-isolation transformers, but I really don't think they
helped much, as the problem was momentary dips. (Later,
shielded cables came in, these have a layer of copper mesh
over the main insulation, so there is no AC field present on
the outside of the cable. As far as I know, the original
shielded cables are still in there, once they got all the
old unshielded stuff out, these problems just stopped
Anyone run any of this stuff at home / light
We tried to get a 370/145 running at a guy's house. That
had the 17 KVA motor generator set in the back (WAY more
than a 145 needed, but they apparently used one MG set for a
range of machines). But, he only had 60 A 240V single-phase
service, and we couldn't even spin up the MG set with no
load. We built a static phase converter, but the imaginary
current was over 60 A. Well, NO SURPRISE, if we'd just read
the nameplate we would have known it was a fool's errand.
The 3-phase line current on the thing was about 55 A, per
3-PHASE LINE, so running it off SINGLE-PHASE, the line
current would HAVE to be 1.7 X that much, wouldn't it? OF
We should have just scrapped the original 415 Hz power
supplies and got our hands on a bank of 5V supplies and
adapted them. The thing ran off +1.2 and -3 V supplies at
390 A, although I think that was for the max configuration,
this one had minimal internal memory, so should have been less.