[Milsurplus] Crystal Current

[Richard Brunner]

D C *Mac* Macdonald wrote:
> I seem to remember something from back in the 50s
> about benefits of a Pierce (or modified Pierce) crystal
> oscillator circuit that it used far less crystal current than
> other circuits.  The modified Pierce used the screen
> instead of the plate.  In other words, even lower crystal
> current than the original Pierce and far greater frequency
> stability of the output.  No chirp with direct cathode
> keying of 6AG7 and similar tubes.
> 
Yes, but the crucial thing is you must use a "true" pentode, with the 
suppressor grid independently brought out, like the 6AG7 or 837. 
Beam-power tubes like the 6L6 are not the same thing, and are noted for 
high crystal current. (rock-crushers)  You also must have sufficient 
shielding so there is no magnetic feedback path or you will have high 
crystal current even with a 6AG7.

Richard Brunner, AA1P