[AMPS] SB-200 tuning problem

[Michael Rudzki]

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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