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The 3CX1500A7 is a nice
valve to play with. Some more talented individuals use tetrodes,
but triodes are surely the way forward for the majority, provided that you
have adequate drive - about 60W.
The W6PO design was straightforward to get going, the tank resonating at
130MHz before adjustment of the anode lines. I had more trouble with the
cathode circuitry, and couldn’t use the original design.
Control circuitry, bias and filament supplies are placed in a separate unit. The
intention was to be able to power a second amplifier on HF, but that project
has not happened. I've not had an HF contact in three years. Now I have a
3CPX1500A7 in the VHF amp, so the original valve is spare. The HF project could
happen, once all the other ideas are taken care of!
Results:
I treated myself to a new Bird 43
power meter and 1000C element for the final tests. Once it became apparent
that there was sufficient RF to end-stop the Bird 43, I had to buy a 2500C
element. I have paid more for the power meter and its sampling elements than
I have for the amplifier! Be aware, once you have a Bird 43, you’re in danger
of collecting more and more sampling elements for it..
FT-225RD, 25W in gave 600W out.
SD1416, 70W in gave 2.2kW out.
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