[R-390] FL-101 replacement Corcom IEC power Filters

[Bill Hawkins]

There seems to be some confusion about the meaning of leakage.

Capacitors are said to be leaky when their insulation resistance has
decayed with time, and we are dealing with long times in these old
radios.

GFCI's are tripped by about 5 MA of "leakage" current from the radio to
ground, regardless of its source or phase angle to the line.

A capacitor of 0.1 mfd with very high insulation resistance has an
impedance of about 27 K ohms at 60 Hz, from Z = 1/(2Pi*f*C) (C in
farads). Line voltage of 120 volts produces a current of about 4
milliamps, and two of them produce 8 MA, enough to trip a GFCI.

So when someone says a filter is leaky, they are not talking about the
leakage that comes with age, yes?
They are talking about the reactive leakage current that occurs with
capacitive reactance at line voltage and frequency, no?

In other words, a brand new R-390 class filter will trip a GFCI even if
it shows infinite DC leakage resistance.

In other, other words, a filter that does not trip a GFCI has to be less
effective than the original because it has less capacitance to ground.
And it is that capacitive reactance at RF that makes the filter work,
with the aid of some series inductance.

Does that clarify leakage?

Bill Hawkins

P.S. Earlier, I failed to mention that a significant amount of line
noise was produced by the generators at field locations. That would
account for the large capacitors in the filter. Switching supply
frequencies are much higher than 60 Hz, allowing smaller caps to be used
in filters for today's conditions. Collins actually tried a switching
supply (with thyratrons) to allow the radio to use 115 VDC as a supply.
This supply replaced the 60 Hz power transformer inside the radio. It
was abandoned, along with an internal dynamotor, because there was too
much electrical noise to meet the sensitivity specs. See the Engineering
Report.