Recently I carried out some tests on my new Henry Radio SS750HF amplifier. This
amplifier contains 8 2SC2879 transistors; it has 4 modules each with two
transistors and splitter-combiner circuitry.
This amplifier is speced at approximately 750 watts CW output (50% duty cycle)
with 100 watts drive. My results were significantly poorer on 14 mHz and
higher; the test procedure and results appear at the end of this message.
Henry tells me that the results I've gotten are normal for this amplifier, a
result of the characteristics of the semiconductors used, and they've offered to
give me my money back if I'm unhappy. However, the convenience of this
amplifier (no tuning, relay-controlled bandswitching) leads me to want to keep
it and improve the performance. Does anyone have any suggestions?
Here is the test setup and the results I've gotten:
Power supply voltage was 13.8v under load at all times (from two parallel Astron
70 amp supplies feeding the amp through 10 feet of 2/00 welding cable). The
output was fed into a dummy load; swr to the dummy load ranged from 1.08:1 on
1.8 mHz to 1.3:1 on 28 mHz. I measured the power output in CW with 100 watts
drive in each case; on those bands where I was unable to get 750 watts output at
this drive level, I
increased the drive to the maximum available.
Wattmeters were peak-reading (RF Applications VFD) and drive was pulsed (50%) to
reduce the strain on the amplifier. Transmit periods were as short as possible
with rest periods in between. Current measurements were approximate, made by
multiplying the reading on the analog power meter on the amp by 2.
Note the sharp dropoff in output at 14 mHz and above. I suspect that the 12/10
meter readings are too high, since the swr on the dummy load may be beginning to
affect the reading.
Band in out amps
---- --- --- ---
160 100 955 90
80 100 1036 90
40 100 995 90
30 100 790 90 (20m band switch activated)
20 100 611 80
" 170 698 84
17 100 654 88
" 138 756 95
15 100 530 90
" 122 570 90
12 100 550 80
" 138 590 100
10 100 611 75
" 110 622 80
73,
Vic, K2VCO
Fresno CA
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