[AMPS] SB-1000 bandswitch damage

[Rich Measures]

>I was looking through the Amps archives and I noticed some comments about 
>damage to the 160-meter padding capacitor bandswitch contact due to Heath not 
>providing a
>corona washer.  
Corona at 2800pV on a 5000pV capable bandswitch?
> Sure enough, my SB-1000 has a burned bandswitch contact in 
>this place.  I'd put off fixing it and attributed it to the former owner's
>hot-switching...but maybe that isn't what happened after all.
The SB-1000 is essentially an AL-80, and whose replacement parts happily 
fit.  
>Could someone please educate me with regard to this?  What causes this 
>problem, and what kind of washer needs to be put where to prevent it?  
Replacing the 
>contact is going to be annoying (I really don't want to replace the whole 
switch) and 
>I only want to do it once!
Open160m tune padder switch contacts tend to arc during intermittent vhf 
regeneration. at roughly 155MHz.   If you couple a dipmeter to either 
side of the hv dc blocking cap. you just might see a sharp dip near this 
freq.  You can find some photos of parasite arced bandswitches at:
www.vcnet.com/measures
-  It is my opinion, based on conversations with the owners, that none of 
these bandswitches were ruined by "corona", "operator error, bad 
antennas, or by cheap coax". {Charles Thomas Rauch, Jun., W8JI}  .  The 
likely fix is to replace the burned contact, or to replace the wafer if 
the ceramic is blackened with metal vapour condensation, and to decrease 
the vhf Q of said vhf-resonant circuit.  
-   later, Vic

cheers
Rich...

R. L. Measures, 805-386-3734, AG6K   


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