[R-390] Some questions?

[Tim Shoppa]

> applying variable DC to one side of the capacitor and with the DC milliamp
> meter checking the current through the capacitor.  Is this a good
> indication of the leakiness?

Well, a milliamp of leakiness at 200V is way more than spec (that's
equivalent to a 200K resistor in parallel) so I think you'd like something
sensitive to the microamp level.

Many of the brown beauties are installed in places where leakiness
is almost a complete non-issue.  For example, the bypasses on the crystal
oven on the RF deck, or the bypass on the IF deck for the ballast tube
chain.  If the capacitor was so leaky that it was like a 1K resistor then
it wouldn't matter in those applications.  In other places, where it's a
screen bypass or B+ bypass, a milliamp of leak will substantially disturb
the intended operation of the circuit (although the radio will probably
seem to work fine still.)

Because the brown beauties are installed in rather non-critical areas,
you might want to check out the capacitors that usually are Vitamin Q's/
Westcap hermetically-sealed-cans as well for leakage.  In some of these
circuits a microamp of leakage might be too much, so upgrading your
test scheme to be more sensitive would be necessary before getting to these.

Tim.