[AMPS] Cathode input networks resonant or not?

[Richard W. Ehrhorn]

I submit - admittedly without PhD-level academic documentation but based on 
hands-on experience - that if the cathode network isn't resonant at or 
fairly near the operating frequency there's no "flywheel." With no flywheel 
(a) the input impedance is highly non-linear - much like a series rectifier 
and resistor/capacitor combination - and (b) the cathode voltage waveform 
has very high odd harmonic content.

The anode load seen by the harmonic components is largely reactive, so the 
harmonic components of rf plate current contribute only to plate 
dissipation, correspondingly reducing plate efficiency at the fundamental 
frequency. The magnitude of this effect varies with the exciter and the 
length of drive cable, but typically a g.g. amp that delivers ~65% 
efficiency with a resonant cathode network of Q  2-4 may drop as low as 50% 
efficiency with an untuned input, or with any LC input network/filter of 
effective Q </= ~1.

These comments are based on practical observations, but I believe they're 
fully consistent with what one would expect based on circuit theory.

73,    Dick  W0ID

-----Original Message-----
From:	John / NS1Z [SMTP:ns1z@agate.net]
Sent:	Friday, August 28, 1998 4:27 AM
To:	Rich Measures
Cc:	amps@contesting.com
Subject:	Re: [AMPS] Low Output on 10 meters


OK, time for amps 101 again:

I'll concede the pi is back to back Ls but, if it is not resonant at the
operating frequency, what is it that everyone is tuning it to....

At 02:27 AM 8/28/98 -0800, Rich Measures wrote:
>
>A pi-network is two L-networks in series.  It is not resonant at the
>operating frequency
>>_______________________________________________________________


John Wilcox  NS1Z
FN44rn
ns1z@agate.net
fon: 207-364-2246

871 Route 120
Rumford, ME 04276-3836

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