[Boatanchors] Choke voltage rating

[Brian Clarke]

Hi Vic,

If you're concerned about flashover, connect the choke in the negative side of the filter instead 
of the positive. In other words:
  a.. Tag-strip point #1 has the transformer centre-tap+one lead of the choke+the negative 
  lead of one electrolytic capacitor;
  b.. Tag-strip point #2 has the other lead of the choke+the negative lead of the other 
  electrolytic capacitor and is your negative output lead - may be connected to chassis;
  c.. Tag-strip point #3 has the cathodes of the rectifiers+the two positive leads of the 
  electrolytic capacitors and is the positive output lead.
It's still just a Pi-filter. The only Voltage between your choke and the case now is 
IR + L di/dt when the current changes.

If you want to be really scientific, you could always conduct a flashover test - connect a 
variable high voltage, current limited power supply between either lead of the choke and the 
case; measure the leakage current with a very sensitive Ammeter - you're looking for 
micro-Amps. Increase the Voltage very gently, in case there is a flashover - so, protect 
your Ammeter - a 1 Amp 1000 V diode across the movement should do.

One problem with older-style potted inductors - and transformers, too - is that the seal 
between the porcelain and the steel gets jeopardised, often from the inside, because not 
all moisture was removed from the winding, laminations, former and insulation.

73 de Brian, VK2GCE.
  You sought reassurance, and possibly guidance:

  I have a choke marked Milwaukee Transformer Co. (various numbers), 4 Hy @ 160 MA 
  DC, ... WV 500.  It's encapsulated in a nice steel box and also marked "MIL-T-27 
  Grade 1 Class A"  Obviously potted and the case looks soldered shut.  Porcelain 
  terminals.

  It's probably OK to operate this choke in true ham spirit in a 750 volt supply, 
  right?  The case will be well grounded so the worst thing that can happen will 
  be a blown fuse.

  On the other hand, maybe someone will say "no, you really have to believe the 
  voltage ratings on this kind of stuff!"