[R-390] Caps

[Charles P. Steinmetz]

Sam wrote:

>CDE still makes 3 versions of axial-lead film/foil capacitors. 
>Series WMC, WMF and WPP.

400 Vdc is the highest rating available in the WMC line, due to the 
thinner dielectric used to miniaturize them (and note that 0.001 uF 
is the only value Mouser stocks).  Although they are cataloged, I 
have not seen WPPs above 400 V stocked by anybody for years 
(decades?), and even the lower voltage ones are very scarce.  If you 
can find some 600/630 V WPPs, they should work fine.

Some might ask why I think 600 V caps are necessary.  I assume (i) 
that the entire power supply voltage of a radio could appear across a 
cap under failure conditions, and (ii) that unforeseen faults (or 
even foreseen events, like the turn-on surge in radios with 
solid-state rectifiers) could cause the actual power supply voltage 
to exceed the nominal value.  In the (unlikely) event that both were 
to happen simultaneously, a 400 V rating is marginal for most 
BAs.  Thus, my recommendation to use 600 V capacitors in BAs.

Best regards,

Charles