>
>I have a FL-2100B that does not work on 80M because the bandswitch has a
>contact that looks like it was vaporized.
>
? My guess is that it is the 80m Tune-C padder contact.
>I am looking into getting a replacement bandswitch from Yaesu, but would like
>to know of any other sources.
>
>Also, I would like to know if anyone else has had a similar problem with one
>of these amps.
? ......many reportedly have. Some SB-200 owners report the same
problem. In the early 1980s, Yaesu issued a service bulletin saying that
the problem was due to vhf parasites. Unfortunately, the recommended
modification did little to reduce the gain of the 572Bs at the
anode-circuit's vhf-resonance. . To determine whether you had a
parasite, measure the resistance of both anode parasitic-suppressor
resistors. An increase in resistance of more than 50% in one or both
indicates that an intermittent parasite payed a visit.
> It was broken when I got it, so I don't know the failure
>situation. I am curious if anything else might have been damaged either
>before
>or as a result of the bandswitch failure. I have visually inspected and find
>nothing else appears to be burned or overheated.
>
? In some cases, electromagnetic stress during an intermittent vhf
parasite is sufficient to shatter a 572B's filament. In 3-500Zs, the
filament can bend during such, sometimes shorting against the grid. {see
photo on p.15 of Sept, 1990, *QST* magazine}
- later, Mike
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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