I made a set of interesting measurements with my spectrum analyzer on a
Drake TR-7 driving a L-4 amp. Set the output at 1kw through a W-4
wattmeter into a dummy load. Harmonics looked good, down quite a
ways. Crank the TR-7 up a bit to the L-4 and the power went up to 1100
watts. The fundamental stayed the same, it was the harmonics that went
up! The power meter didn't care what frequency the energy was. Now I
always run a MN2700 pi network antenna tuner with any of the Drakes.
Larry K2LT
drakerepair.com
800-687-9161
Efficiency is often a function of the tank circuit Q.
Lower Q often gives more efficiency.
It can be quite dramatic if you are far off.
Grid bias needs to be way beyond cutoff, and with a
lower Q, efficiency should go up.
I did some experiments on the push pull 812 rig when it was done.
I was getting 200 watts out of it, until I shorted 2 or 3 turns
on the final coils.
Power went up 50 watts!
I removed the turns to prevent weird stuff going on, but still
only got the 250 watts out, so the shorted turns were not
causing problems in my application.
Maybe try shorting some tank coil turns as a test and see what happens.
If you left a lot of turns in the coil, your Q could be above 20 or more.
>From memory, a Q of 15 is 'normal'.
A Q of 12 should be ok, who has harmonics these days?
Brett
N2DTS
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