PDP 8a transformer capacitor replacement?

Paul Berger phb.hfx at gmail.com
Thu Nov 19 07:01:09 CST 2015

On 2015-11-19 6:20 AM, Brian Walenz wrote:
> Having read all sorts of bad things about these older oil filled
> capacitors, I decided to replace the one on my 8a.  I got what I think is a
> replacement - 6 microF, 660VAC, 50/60Hz, "NO PCB's" - but it is physically
> about 1/3 the size as the original.
> Did the tech for these get that much better?
> What purpose does this serve?  It's hanging off the transformer.  I see
> lots of links about motor start capacitors, but nothing relating to
> transformers.
> http://www.mouser.com/ProductDetail/Cornell-Dubilier/SFA66S6K288B-F
> Thanks,
> b
The capacitor is likely on a separate winding and the tank circuit 
created by this winding and the capacitor works to regulate the output 
voltage also referred to as a "Constant Voltage Transformer".  If this 
capacitor goes short you get zero output from the transformer a lesson I 
learned early in my career as a service rep.  When the capacitors are 
going bad they will sometimes swell up and even burst.  Early capacitors 
of this type where filled with an oil that contained PCBs but by the mid 
70s some manufacturers had replaced them with capacitors that did not 
contain PCBs on all in service machines.


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