Here are some thoughts after a weekend using the SB-200 during CQWW SSB.
Firstly I will never get over the difference it made. I started with the amp in
standby (I built my rig to amp interface and included a bypass switch in it
rather than in the amp itself) thinking that I would only use it if NECESSARY.
When the first station I called did not answer after 3 tries I tuned it up and
flipped the switch. BANG, he came back to me on the first call with the amp. I
tried the same thing a few more times with exactly the same result so the amp
stayed in the contest till the end. I will have to upgrade the TV cabling as
the bride says it puts lines in the TV and makes the picture BLOOM sometimes. I
think an S-Video cable from the satellite box to the TV should cure that and I
had been planning to do that anyway.
The amp is really tolerant during tuning. The TUNE control has WAY more effect
on the output than the LOAD control does. In fact, while I have not gone
through and built a TUNE/LOAD chart for the different bands I would be willing
to wager the LOAD control is always between 4 & 7. The peaks are rather sharp
with very little gained after the first tune up on a frequency. I am using an
old Heathkit HM-102 as an output meter, so I really don't know how much power
it really is putting out. I will borrow a Bird and run a calibration between
them to see how close the HM-102 is, (I am not counting on it, but it is a good
relative reading of power).
To tune the amp, I am running into a cantenna and putting the radio in RTTY and
using the TX button to key the radio and amp. The GRID CURRENT rarely gets over
mid scale requiring me to turn down the power. I am running about 50 to 70
watts during tune. I did crank the radio back up to 100 watts when I noticed
that the GRID CURRENT (I leave the meter switch in that position since I think
it is the greatest indicator of how I can damage the amp) was barely moving
during SSB TX. I imagine that would not be true for CW and RTTY. During
tuning I watch the HM-102 for max and the GRID CURRENT for max center of meter
scale.
I resorted to using a headset for the contest as the fan is noisy. Not really
bad, but annoying enough to want to block it out when trying to dig my callsign
out of the noise and the pile up. Harbach sells a replacement. Should I get
one of those or would a muffin type fan be better and quieter? I might
consider two muffins, one top and one on bottom to get the air flow without the
noise.
Since I am going to open up the amp should I consider changing the RCA jack
input to an SO-239? I have a RCA to SO-239 adapter into an L connector to feed
the RF to the amp. I do not use ALC since two hams whose opinion I respect
have said it is not necessary. One went so far as to say ALC stands for
"Automatically Limits Contacts". Also there is no adjustment for the ALC on the
SB-200 so the set up with my IC-756 would be problematic.
As always I invite comments, suggestions and answers to my questions are always
welcome.
Clint - W5CPT
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