There were a few things I left out of this last post:
I already checked the pointer alignment. at one end it is fully
meshed and at the other end it is fully open.
The rig I am using for an exciter is a Yaesu FT-920. At first I used
it without the automatic antenna tuner, but now I use it with the
tuner enabled. Either way, it has the same effect.
I tried setting the TUNE cap within the desired band and adjusting
the load for max output, varying the TUNE within the band range.
This never worked. The most I could get out of the amp is 100 watts
- what I get with the 920 barefoot.
I checked the band switches and found that some of them were
tarnished very slightly. I cleaned them with Tarn-X and cleaned them
again with alcohol (in case the Tarn-X left a residue). Same thing.
I haven't tried playing with the tuning slugs. Is this the key?
Thanks and 73,
Mike, N8MR
At 01:58 PM 12/8/00 -0500, you wrote:
>
>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
>
>
>--
>FAQ on WWW: http://www.contesting.com/FAQ/amps
>Submissions: amps@contesting.com
>Administrative requests: amps-REQUEST@contesting.com
>Problems: owner-amps@contesting.com
>
Mike
kf8bex@oeonline.com
--
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