[Milsurplus] 12BY7 with tiny crystals?

[Bob kb8tq]

Hi

Crystals went from “current ratings” to “power” back in the 1950’s. Anything over
0.1 mw is a lot by modern standards. Anything over 1 mw is in the “to much” range. 

To do the conversion ( current to power ) you would need to know the resistance
of the crystal. Something like 2X the frequency in MHz is probably the lowest ohm
number you would ever see on a fundamental HC-49. On a third overtone, triple that
number. 

From P = I^2 * R, a 10 MHz crystal at 20 ohms and 10 ma gets you to 0.01 ^2 * 20. 
That’s 2 mw assuming my calculator skills aren’t to far off. 

Bob

> On Jun 3, 2022, at 8:31 PM, Hubert Miller <Kargo_cult at msn.com> wrote:
> 
> It seems a little obscure what the hard numbers on crystal current are, at least in my experience.
> I have some lit on the design of the TRC-10 and this says that prelim design rejected because FT-243 crystal current is in the range of 100 mA.
> For sure the little critters would have much less current capacity.
> -Hue Miller 
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