>
>In Class A, a g-g amp has an input impedance of 1/gm. What happens in Class
>AB or B is another matter. Since the gain is approximately the ratio of
>cathode volts to plate volts (because plate current is common to both
>circuits) I surmise the input impedance can be determined from Pin/(Ek
>squared). That means settling down with the tube curves and working out the
>volts and amps over the cycle.
>
? Meanwhile, back at the chassis, a rather accurate representation of
the complex Z exists -- the cathode itself. Set C-in for a Q of
c.2/XC-in=25-ohms for each band, adj. L and C-out for a match, adj. C-in
if needed, measure L and C-out, replace with fixed values. Repeat for
other bands. The End.
>Using the resistors is fine if you know the value to shoot for - as Jon did.
>If you don't, then the whole thing is probably more miss than hit. It's also
>complicated because you're relying on the tank circuit Q to keep it free
>wheeling, while for best linearity, you really want to make the feed
>impedance very high - see Pappenfus et al.
? To make the feed Z high, a lower Mu triode could be used?
>
- cheers, Peter
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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