>
>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) ...
This is caused by the use of 30k-ohm cap. equalizers. For less toasting,
change to c. 100k-ohm.
>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?
>
The bandswitch contacts?
cheers, Mike
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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