[AMPS] 572b's as a robust oscillator AHHHHHHHolla Ceeeee

[Tom Rauch]

Hi Jerry, 

Yes, you certainly do need bifocals.

> >But I can tell you that 8000pf and it shunted by a .1µh inductor then
> >placed across the input to ground works on 160m. Fair enough for tube
> >type exciters pushing a pair of these on 160m. I'd say scale it to
> 50mhz.
> >Oughta be close.

As I said, scaling won't work. You assume, quite incorrectly, the 
tube provides the same input impedance on six as it does on 160. 
Not a chance.

The 8000 pF you used is 11 ohms on 160. If we place that in 
parallel with the correct inductor, the Q is somewhere around 10 on 
160. There must be some specific reason you selected a Q of ten, 
I wonder what it was?

> Tom if your going to  quote me make it complete.  AGAIN I SUGGESTED ONE TO
> SCALE THESE VALUES. Bifocals stink huh |-)?

OK, then me repeat it and maybe you will understand what I wrote.

The lead lengths and stray capacitances, as well as the much 
different grid impedance, will certainly change the input impedance 
of the tube a lot on six meters. There would be a snowballs chance 
in hell the values that worked on 160 would work on six, when 
scaled to six meters.

Is that clearer?



> 
> 73,    Jerry                                     krr2ak@juno.com
> [text|uuencode|59kb ea]                                     
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73, Tom W8JI
w8ji@contesting.com

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