>>? Assuming that a g-g input is like a resistor is bound to bring some,
>OK for all of you who doubt it then. What other assumption can one make?
>The tube is spec'd for an "average" driving impedance of 110 Ohms with an
>input capacitance of 27 pF. Last time I looked, Ohms was a resistance
>value (hence using a resistor) and pF was a capacitance value (hence using
>a capacitor). Sure there could be some inductance in there too. However,
>the resistors and cap had some lead length which add a little bit of
>inductance as well.
>So......if you have all 3 passive sorts of components covered.....what
>else could it be???
? The cathode is like a diode that is driven with pos. and neg.
potentials. Heavy current flows on neg. No current flows on pos. A
resistor this is not.
>Now, I KNOW that in a GG circuit, the input impedance varies over the
>drive cycle. But you have to have some sort of impedance that you use to
>create your input match. A pi-net or an L-net or a T-net match one
>impedance to another in addition to being like the venerable flywheel and
>storing energy. So one end is 50 Ohms, pray tell to all you out there
>what the other end is? Well, I used what the data sheets say is the
>driving impedance which equals 110 Ohms. So on paper, you use 110 Ohms in
>parallel with 27 pF (which on any data sheet you find is spec'd as the
>input capacitance). You absorb the 27 pF into the value of C2 in your
>Pi-net and then solve the equation for a pi matching network.
? 110 ohms could be close. In this case, the swr meter in the radio
will work as well as the MFJ-259.
>Now if what they taught me about matching networks in college is all
>wrong, I would like to know.
? In college we learned how to match resistive loads. A cathode is not.
>I KNOW that there are some additional real
>world effects inside the tube that I can't completely account for by
>simulating it, but it should get one relatively close. Otherwise what
>good is working out networks by any form of calculation. Should all of
>our engineering be hit or miss?
? Not at all. Set the input pi network Q for 2. (XC1= 25-ohms). With
full drive, adj. L and C2 for a match to the actual cathode.
- later, Jon
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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