[VHFcontesting] 222 mhz W6PO amplifier questions

David Pruett k8cc at comcast.net
Tue Dec 30 22:07:47 EST 2014


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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