[R-390] R-390 Q of Caps and tuned circuits

[Larry H]

Here's a little more info on the Q of caps used in the R390.  Jordan Arndt
sent me a file from 1966 on the specifications of Elmenco caps made then.
It states that their SM caps were made to the MIL-C-5 specifications at
that time.  I could not find it from around 1960, but did for 1975.  It
states that the SM cap Q must be greater than 1,333.333 for those caps with
a value between 75pf  and 1000pf.  I suspect that this spec did not change
since the 60's.

If someone could find the MIL-C-5 spec from that period and send it to me,
I'd  appreciate it.

This information agrees with what Jacques Fortin measured and posted to
this forum on *Apr 6 23:49:53 EDT 2024:*

I have also run some tests with my HP 4192A Impedance Analyser.
The best 100pF ceramic cap I have in my bins scores a Q of 220 at 1MHz.
A 100pF EL-MENCO from a R-390A RF deck scores a Q of ~1800 at 1MHz
A 100pF EM dipped silver mica pushes the instrument to it's maximum reading:
Q of 2000 at 1MHz !


Since previous information posted here says that the best ceramic cap
Q is around 1,000, this information about ceramic and SM caps
indicates that only good SM caps be used as replacements in the hi-Q
circuits of the R-390.

Regards, Larry