[R-390] Ceramic .01 bypss buy

[Tim Shoppa]

David Wise wrote:
> Tim Shoppa wrote:
>> Or: why did Art not use ceramics to begin with?

> They didn't exist / weren't reliable / were too expensive.
> Ceramic caps were an emerging technology at that time.

But 0.005 ceramic disks were used extensively in the RF deck
and occasionally elsewhere.

The 0.01's sprinkled through the IF deck aren't conceptually
in a different ballpark.

I think that time has proven that the disks are generally more
reliable in bypass applications (at least they don't fail in a leaky
way most of the time like the BBOD's.)

And then there's that funny sandwich of a bunch of ceramics in
parallel in the PTO bypass. I think the Y2K schematic shows these
as a single 0.005 but I have never disassembled a sandwich yet.

And elsewhere in the PTO there's ceramic disks around the thermostat
(although you could easily argue that is definitely the WRONG place
to put wax capacitors.) Other thermostats in the radio use BBOD's
(these are quite definitely NOT CRITICAL usages, only ever a few
volts across them and awful leakage will never ever matter.)

The 0.1 bypasses and the similar and bigger stuff in the audio deck,
I can certainly see why film/wax capacitors would be used there
instead of ceramics. Even modern ceramics would be
completely inappropriate.

I would be willing to believe that different folks/divisions designed
different parts of the radio and they used what they were familiar
with instead of all working from a single master "preferred component"
plan.

Even today for a few hundred volt cap I think the 0.005/0.01 line
is an appropriate dividing line between ceramics and film caps.

Tim.