[AMPS] YC-156 Input impedance

[Tom Rauch]

> 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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