Back in February, I solicited the list's advice on the purchase and repair
of an SB-220 amp. I decided to buy the amp. After replacing the output
band switch (from Carl, KM1H) and applying many of Alan Harbach's upgrade
kits, the amp is operational and seems to be doing OK.
Except for 10 meters, for 1100 watts input power (2200 volts @ 500 mA total
plate current) I am measuring about 600-700 watts out to my dummy load. On
10 meters, output power is down around 300 watts and the input SWR to the
amp is approaching 3:1. I guess I need to rework the 10 meter input tuned
circuit as suggested in several of the upgrade articles. To get that 1100
watts input, my transceiver is driving the '220 with about 60 watts of
power. If I drive the amp with 100 watts from the transceiver, the plate
current goes up to around 650 mA and I measure 850-950 watts out to the
dummy load.
All of the above measurements have been with the amp in the "CW/Tune"
switch position (plate voltage of 2500 unloaded). The "SSB" switch setting
on the '220 increases the plate voltage to around 3100 volts (no load).
Given the higher output power limits the FCC now uses, can/should I run
both SSB _and_ CW on the higher voltage setting? I am concerned that the
power supply might not be able to handle the higher duty cycle of CW at
that voltage setting. Any experience/advice would be welcome.
Thanks,
Nat Davis
N4EL
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