PDP-12 Restoration at the RICM

tony duell ard at p850ug1.demon.co.uk
Sun Aug 9 11:51:58 CDT 2015

> We reconnected the Variac to the input and with 10VAC the high-voltage
> power supply had a 1000VDC output. We put 10x 500kOhm resistors in series
> across the output and increased the Variac voltage. By measuring the
> voltage across one resistor we could see that the output was more than
> 10,000VDC. The resistors started smoking so we knew that we had a lot of
> high-voltage available.

Wait a second! Are you sure those capacitors are electrolytics, because I am almost sure
they are oil-filled paper types. I have never seen an electrolytic with a voltage rating of
5000V or so. And they would not be very high capacitance in that circuit.

I've worked on the VR14, and the EHT module in that is similar (transformer + voltage 
doubler. It's an oil-filled can, the capacitors are certainly not electrolytics. 

Incidentally the oil may well be polychlorinated biphenyl based, if you are worried about
such things (FWIW a friend who worked on _large_ transformers told me the amount
in a VR14 EHT can is not going to do me any harm unless I do something very silly with 
it. Just wash your hands well if you get any on them).

> So, once again the magic of reforming capacitors saves another piece of
> equipment.

You can't reform non-electrolytic capacitors. More likely they are leaky paper types and you
are drying them out.


More information about the cctech mailing list