[AMPS] FL-2100B blown bandswitch in 80M position

[Rich Measures]

>
>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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