[AMPS] 3CX800 Load impedance

[Chartec Laboratories A/S]

I am re-building an Advanced Radio Devices amplifier with 3 x 3CX800. The amplifier
is designed to run on 4 fixed frequencies, thus the PI-L tank circuit and possibly the
input circuit needs to be re-designed to accommodate the amateur bands.

To determine the "operating line" I need the constant current characteristics of the tube.
Do anyone know where data can be found?.
Is it still possible to obtain the Eimac "tube performance computer" mentioned in
Eimac's care and feeding of power grid tubes?, or do someone have any software
to do the job.
Or simpler (for me!) , do anyone know the optimum load impedance, running each tube
at full rating in class AB2. Plate voltage will be around 2300-2400V at full load.
I also need some info on the input impedance. To me it looks like the input impedance
is going to be fairly low (15-16 ohms), making it more difficult to match with a low-Q
pi-network. Could it be an advantage to use a PI-L or an other network in the input-circuit?
I have compared Eimac formulas with the output data from KD9JQ's TAP2-program. KD9JQ's
calculation of the tank-circuit works fine, but the load resistance is not equal
to peak RF-voltage/peak fundamental RF current. The difference is a factor of 2 to Eimac.
Also the input-circuit calculation is wrong ( Rin > Rgrid ).
KD9JQ uses the tubes Grid impedance as reference for the PI-input circuits Q.
I believe that Q = Rin/XCin, where Rin is the source resistance (transmitter, 50 ohm).

Do anyone have experience in rebuilding an Advanced Radio Devices, ARD-230M?

All comments would be much appreciated.

mailto:soeren_pedersen@chartec.dk

Soeren, OZ1FTU


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