Ferroresonant transformer supply repair

Guy Dunphy guykd at optusnet.com.au
Sun Sep 8 20:38:53 CDT 2019

At 04:54 PM 8/09/2019 -0700, you wrote:
>Hi Kyle,
>On Sun, 8 Sep 2019 18:42:06 -0500
>Kyle Owen via cctalk <cctalk at classiccmp.org> wrote:
>> Has anyone replaced the capacitor in a ferroresonant power supply with much
>> success? My current understanding is that the capacitor and transformer are
>> mated as a pair, so replacing just one of them would require careful
>> consideration.
>> The PDP-8/I I'm working on has a 704A in it, with a GE 8uF 660V capacitor.
>> It measures a couple of nF on my capacitor meter, and I was told by the
>> previous owner that it's dead.
>We recently replaced the ferroresonant capacitor in a power supply on the CHM's
>PDP-1. They do fail (thankfully, not often) - and they are not super-critical
>as to value. If the one you're replacing has the same marked value, you should
>be fine.
>PDP-1 Restoration Team, CHM

Yes, that's right. Find something with the same marked capacitance value.
The rated voltage can be the same or higher.
Be aware these are non-polarized caps, NOT electrolytics. They are typically
paper, foil and oil. Best to find a new replacement, as many old-old oil-
insulated caps will contain PCB (polychlorinated biphenyl) oil, which is
severely carcinogenic. Banned, and must be disposed of as contaminated waste.


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