[AMPS] SB-200 tuning problem

[measures]

>
>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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