Here are the results of testing the SS750 (8 x 2SC2879) on 14 MHz. including
collector currents. Someone also asked what the bias voltage is; it is +0.66
volts on all the modules. Testing was into a dummy load whose SWR was < 1.1:1.
In Out Ic at 13.8v
10 142 30
20 262 40
30 368 48
40 420 52
50 460 55
60 500 58
70 540 62
80 560 64
90 590 65
100 611 66
...
170 721 72
Oh yes, one more datum: My 20 meter quad has an swr of 1.54:1. At 100 watts
into the amp with the antenna connected, I get 800 watts out with Ic = 75 amps!
Mu conclusion is that the impedance match provided by the output filter in the
amp to 50 ohms is not optimal, but whatever impedance it is seeing in the
antenna is transformed to something more comfortable for the transistors.
It has been suggested that the wattmeter (RF Applications VFD) is inaccurate
when used with the antenna because the impedance it sees is not exactly 50
ohms. Perhaps this is true to some extent, but the 75 amp Ic reading is not
changed by the SWR!
If this is true it's not a problem on 20 meters; but on 15 the antenna impedance
is not so propitious, and I only get 530 watts into the antenna. It looks like
a solution would be to use a tuner (which would NOT be adjusted for exactly 1:1
SWR). Too bad; I went solid state to be rid of the need to tune up when
changing bands.
In a sense, the 20-meter filter is 'customized' for my antenna, not 50 ohms! I
guess I could also 'customize' the 18-28 MHz filter for a better match to my
antenna on 21 MHz.
73,
Vic, K2VCO
Fresno CA
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