> Wrong, Kimo-Sabe!
> The Eimac data sheet plainly states that typical performance
> (measured data) to 30 mhz that the cathode input impedance
> is 24 ohms. It also states that a resonant input circuit should be
> installed at the cathode, and it is to have a Q of 5 or MORE. This
> assumes an anode RL of 1000 ohms.
Using Eimac's characteristic curves in a software generated Chafffe
analysis all for class AB2:
6000v @ 14000w=30 ohms cathode impedance
6500v @ 12000w=23 ohms
5000v @ 10,000w=19 ohms
Driving impedance depends greatly on operating conditions.
Most 3CPX5000's I have seen are around 18-20 ohms.
> For folks that would go to all the trouble and expense to put
> one of these tubes and then operate it at reduced output, a
> few bucks more will buy you a tuned input circuit with a roller
> coil and two variable caps.
While impedance matching can be accomplished many ways, the
most important improvement of using a tuned input is realized
when the tuned input proveds a very low impedance at the cathode
for harmonics of the operating frequency, especially the low-order
harmonics.
That means where ever and how ever the tuned input is located,
impedance measurements from the cathode looking back at that
network should show a virtual short at harmonics of the operating
frequency.
73, Tom W8JI
W8JI@contesting.com
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