[R-390] Caps

[Drew P.]

Hi All,

Given Charles' scathing indictment of metalized film capacitors in higher voltage applications, perhaps these could be relegated to service only in low voltage applications in our beloved R-390x.  We could use them for cathode bypass and heater bypass.  These are mostly .1 uF and the compactness of metalized film would most welcome.

We could likely use .01 uF or .02 uF disk ceramics in place of the .033 paper caps.  I don't think that there was any magic in the .033 uF value, that is, unless, the designers were thinking of series resonance at 455 kHz to make for a more effective bypass.  In the case of series resonance, we'll never hit upon it by simply replacing the cap with another .033 uF as resonance would be partially determined by the cap's internal inductance, and what are the odds of some other cap having the same inductance (a non-specified parameter) as a Black Beauty. So just toss in some disks having a suitably low reactance, live long, and prosper.

Want cheaper ceramic disk bypass caps to replace the .033 uF?  How about Z5U dielectric, and use .022 instead of .01 to soak up the voltage and temperature coefficients.

Orange drops?  C-553, most definitely.  Also for audio coupling, because the audiophools like them too.  Need at least a token Orange Drop presence in our R-390x to keep the religion alive.  Kinda like people who go to church only on Christmas and Easter.

Drew