IBM 029 Keypunch has arrived

Brent Hilpert hilpert at
Mon May 25 13:46:48 CDT 2009

Roger Holmes wrote:
> Looking through the parts list there is something I'd like the list's
> opinion on. The diagram shows a transformer but the list says
> "REGULATOR ASM, FERRORESONANT-60CPS 120VA" and a similar option for
> 50Hz which of course I don't have. What are these for? Might they work
> at the wrong frequency? Will they be damaged or just not work? This is
> part of a 48v DC supply. Should I build a simple 48V supply myself or
> even see what I can find in my verifier spares?

Ferro-resonant regulators are a type of AC regulator using a special
transformer tailored to operate with the core around the flux saturation level.
Operated in this manner the output is regulated because the amount the magnetic
flux can change is limited.

The transformer has a special winding on it with a capacitor (may look similar
to a motor start cap) connected across, which is where the resonant aspect
comes in, and hence dependance on the operating frequency. I don't know enough
about them to say precisely what will happen when operated significantly off
the target design frequency: whether the output will change, loss of regulation
capability, excessive power consumption/heating, some combination of the
above... other than to say I expect 50 Hz vs 60Hz is more than enough to matter.

To my limited observation, IBM was rather fond of ferro-resonant regulators. I
had an IBM modem/store-loop controller at one time, the logic power supply
being a ferro-resonant transformer (no power transistors anywhere). It's one
reason some IBM equipment seems excessively heavy, the ferro-resonant
transformer (with cap) being typically heavier than would otherwise be required
for the same amount of power.

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