Dear All. I am having problems with the choice of
material for the output network of the 475kHz Valve TX.
The network is an L – C – L, ‘T’ network with an input
impedance of 2100 ohms and a load of 50 ohms, for this configuration the input
L is 7.7mH, shunt capacitance is 117pf, and output L is 1.1mH. The PA design
using a 6146 low power or 813 high power work fine when simulated using LT
spice IV. When testing in the real world using the 6146 there is in excess of
800v rms rf on the network side of the anode coupling capacitor, but nothing
after the input L. I can only conclude that I using the wrong type material for
the toroids, I used the largest size (unmarked) toroid which gave me a modest
number of turns. I have checked the Amidon tables and Iron Powder because of
the low AL
values, which leaves Ferrite, which mix would you recommend? The simulations
give me output powers 90W for the 6146, and 300W for the 813. I would be
grateful for any core material advice .
Ken Wright.
M0KHW
