I have an SB-200 (S/N 13643) and I have been having problems
tuning it, especially on 10 Meters. I got it off e-Bay for a good
price and it seems to be in otherwise great condition.
When I tune the amplifier on any band to what I believe is the
correct resonance, the pointer on the TUNE knob never points
to the correct band, as marked on the cabinet. It always peaks
the REL PWR output at a point further to the left of the band
scale (with plate current within the specified limit). It is always
impossible to tune the amplifier within the proper band scale
markings.
Secondly, tuning the amplifier on 10 Meters is quite a battle.
It usually takes me at least five minutes to tune that thing to
anywhere near 400 Watts of output power. Right now, I know
it's tuned to the CW portion of the 10 Meter band and I don't
want to touch it, for fear of losing that resonant point.
The two situations occur when I am tuning into either an antenna
or into a dummy load. I used several types and lengths of coax,
with the same results.
I tried replacing the tubes with NOS, but that didn't help. I also
checked the components for physical damage and excessive heat.
Nothing seems to be burnt (except a little discoloration on the power
supply PCB) and none of the coils seem to be open.
Is this normal for an SB-200 of its age? Is there anything I am
overlooking?
Thanks and 73,
Mike, N8MR
n8mr@arrl.net
Mike
kf8bex@oeonline.com
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