I had the same problem with an SB-200 bought off the web.
Check Rich Measure's web site for Figure 9 - Tuning Pulser. There is a
brief description of how to tune a grounded grid amplifier included.
Disregard the markings on the face of the amp and follow Rich's instructions
and all will be well.
Steve W4IMF
----- Original Message -----
From: "Michael Rudzki" <kf8bex@oeonline.com>
To: <amps@contesting.com>
Sent: Friday, December 08, 2000 1:58 PM
Subject: [AMPS] SB-200 tuning problem
>
> 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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>
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