[R-390] Bypass capacitors, R390 and SP-600 [WAS: saga continues...]

[Shoppa, Tim]

Don writes:
> Finally, I thought I saw a message recently about re-capping a
> Hammarlund SP-600, and the poster quoted a number of replaced caps
> that sounded very low to me.  My recollection was that there are
> nearly 60 paper bypass caps in an SP-600, and every single one MUST
> be replaced due to their 99-point-something percent failure
> rate.  Chuck Rippel's web site puts the number at 57.  So when you
> are replacing paper bypass caps in an SP-600, make sure you get them
> ALL.

I have to really doubt anything like a 99-point-something percent
cap failure rate as applied to usability of the radio.

That number was probably based on some original manufacturing
spec for capacitor leakage. And I don't really doubt that it's true, as measured
by hooking the cap to its rated voltage and looking for leakage above
a fractional microamp or whatever its original spec was.

I have no doubt that old paper caps have way more leakage than
new ones. And that this can be important in high impedance circuits.
Grid coupling circuits, absolutely, replace that sucker!

But in a filament or cathode bypass, who cares that leakage at
300V rated voltage is in the microamps and above the original cap
spec? Half the paper caps are being used at
6.3VAC or 3-7VDC, and they could be leaking milliamps without affecting
the circuit.

The attitudes of some towards recapping, make me wonder if they
are maintaining a radio, or a box of caps. I mean, if you like looking
at all those nice orange drops or shiny ceramic discs, knock yourself
out. (Personally I like the big light blue colored Murata HV ceramic discs).

But I'd rather be using the radio. Replace the ones that'll make it work
or work better.

Tim N3QE