Interesting. I have build 600W amp with four Motorola MRF150 transistors and I
can easily
get 600W output with 7W input. This was tested with input attenuator removed.
Are those Mosfets in KPA500 that much different?
I also would like to purchase the KPA500 but only if I could get 15 dB gain.
It would be great to drive KPA500 with KX3 10W and get around 300W output power.
I’m pretty sure that KPA500 has some form of attenuator at the input.
Mark WQ7X
But I would buy a second KPA500 in a heartbeat if I knew I could >modify it for
10 watts drive for full output! I think you're being optimistic about full
output with 10W drive.
The VRF-2933 is rated for 23 dB gain (typical). With perhaps 1 dB loss
in the low pass filter, a dB or so in the output transformer, roughly 3
dB in feedback to improve linearity one dB in the input transformer,
bias decoupling, gate balancing, and two dB in the input matching comes
very close to the roughly 15 dB gain limit in the US regulations.
Some of those values are based on application notes from Motorola,
MicroSemi and APT for similar MOSFET designs while some values are
from Elecraft designers. In any case, the inescapable conclusion is
that there is no "magic modification" to get the additional 2 - 3 dB
of gain necessary to get 600W with 10W of driver from the KPA-500.
73,
... Joe, W4TV
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