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[AMPS] SB-1000 bandswitch damage

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Subject: [AMPS] SB-1000 bandswitch damage
From: (Phil Clements)
Date: Wed, 11 Mar 1998 14:59:14 -0600
At 09:50 AM 3/11/98 -0800, you wrote:
>>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
>>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 
>>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:
>-  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.  

This happened to a SB-1000 that I constructed during its first few hours
of operation. I agree with Rich on the fix. I installed the entire kit
provided by Rich and never had another problem. I went with a new band switch
from Ameritron. Rich is again correct when he warns you about residual carbon
on the ceramic wafer. If the arc doug a path it is almost impossible to
remove 100% of the carbon and the switch will no longer retain its voltage

One of the weakest components in the SB-1000 is the 160 meter load padding
doorknob cap. Ameritron has solved this problem by replacing it with a mica
unit which is also available from them. This is cheap insurance to change out
the cap while you are "in the area."

I would like to know if any of the Ameritron clones of the SB-1000 have had
band switch failures, or is the problem entirely unique (and very common)
on the SB-1000?

Phil, K5PC

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