Mike,
You might have the amplifier loaded too heavily. Try reducing the
loading slightly (plate current will drop) then adjust the plate tuning
to peak your power output (which should occur at the plate current dip)
Check the efficiency - if it improves you're likely moving in the right
direction.
Also, take note of your drive level and grid current. Your drive level
should be something like 50W, and grid current should be in the normal
range (check the W6PO article for normal operating conditions). As you
tune the plate tuning, the plate current should dip and the grid current
should peak at the same position of the plate tuning. If your grid
current is low and the tune peak is flat, you're probably loaded to heavily.
Under loading (too light) causes the grid current to run high, heavy
loading keeps it down (a good thing to avoid damage to the tube grid).
slight heavy loading at legal amateur power levels won't hurt the 8877
because of it's rugged plate, put excessively heavy loading can cause
the inefficient condition you describe.
I have one of the AntennaWorks 2M W6PO-style amps and found that the
above tuning recommendations worked pretty well.
73, Dave/K8CC
On 12/30/2014 8:39 PM, mike repinski via VHFcontesting wrote:
I recently finished a 222 mhz amplifier. I get 1500 watts input and 200 watts
out. Not very efficient :( Could anyone shed some light? Not very
complicated, not sure if I am missing something? Mike
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