[AMPS] Tetrode Maths? Grid Terminations

[vk3bvm@talk21.com]

I am building a single 4cx400 amp, i am just about finnished with this project but need some help on the grid termination.

Reading Measures web page it seems that 12.5, 50, 200, and 450 ohms seem to be the practical choices. Assuming I require about 30 volts drive on the grid, i was trying to calculate the drive power.

Using square root P X R  ,,i calculate that it is 20 watts into a 50 ohm load, or 5 watts into a 200 ohm load or 2 watts into a 450 ohm load. This does not include the voltage doubling or tripling effect of the matching toroid transformer. In the case of the 200 ohm load and the voltage doubling transformer i would only require 1.2 watts(square root P X R X 200 ohms X 2 for a voltage doubler)  In the case of the 450 ohm load that would equate to 500 milliwatts using a voltage tripler.

 What i would like to know if this is the correct way to calculate roughly the required drive power based on the required grid volts. I am using a QRP 5 watt transceiver otherwise i would just use 50 ohms and be happy.

Thanks
Byron
VK3BVM



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