Jeff Blaine wrote:
>
> 4.00 mhz 73w drive Po=985w Ip=0.62A B+=2420v Pin=1500w
> 60.8%
> 3.75 mhz 71w drive Po=985w Ip=0.645A B+=2400v Pin=1548w 59.0%
> 3.50 mhz 73w drive Po=1000w Ip=0.710A B+=2375v Pin=1686w 55.0%
>
Looks to me like you are running too much loading for the amount of
drive. Do you have enough range on the load cap? I ran a few numbers and
it looks like you would need at least 500 pF additional load "C" on 3.5
vs. 4.0.
My 432 amp runs about 35 watts drive to a pair of GI-7B's, get 600+
watts out with 2050 volts on the anodes. (My stripline half wave
resonator runs a measured Q of several hundred and has about 15% loss)
At 40 watts drive for the pair, the grids show definite signs of running
hot. Unless you have a very lossy input matching network, 73 watts seems
like far and away too much power to run into those tiny grids even on HF.
With 2400 on the anodes (close to the point at which these tubes like to
flash over inside) the gain on HF should be at least 13 dB including
circuit losses which would mean 50 watts total drive required for 1000 out.
73, Larry
Larry - W7IUV
DN07dg - central WA
http://w7iuv.com
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