If I had them here, I'd just check them on my capacitance meter.
Let me hazard a guess, however. The 482Z suggests that they
were a non-standard(?) value of 4800 pF with the "Z" tolerance,
which is +80%/-20% if I remember right. With the circle around the
M, I would rule out that being the M tolerance of +/- 20%. That is
probably your manufacturer. Possibly Murata-Erie. The 709A and
809A are almost certainly date codes. The 20KV is self-explanatory.
They may or may not be rated for high RF currents. Some doorknobs
are and others aren't. Hams have been getting away for years with
using the old Sprague 500pF/20KV units in amplifiers, though they
supposedly aren't up to it like the Centralab 85X series (now made
by High Energy Corp/HEC) are. Judging from the size and the ratings,
they ought to do the job. (Anybody on the reflector know different?)
David Sinclair K3KY
On Sat, 28 Mar 1998 00:53:06 +0000 W7CW Jay E Ostrem <email@example.com>
>I've got two ceramic doorknob caps that a friend gave me, stating they
>would make good blocker capacitors. They are both 7/8 inch thick, 2
>inch diameter, white in color, with threaded holes for screws. Both
>same manufacturer, The "M" has a circle around it.
>Any help would be appreciated.
> 73 Jay W7CW
> 1AB Ranch
> Gillette, Wyoming
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