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[AMPS] explain this one

To: <amps@contesting.com>
Subject: [AMPS] explain this one
From: measures@vc.net (Rich Measures)
Date: Sat, 31 Jul 1999 13:13:06 -0700


>
>Alek Petkovic wrote:
>> 
>> When I tune up on 10m, I get arcing on the 160m position on the bandswitch
>> to the frame of the switch. This position switches in the 160m padding
>> capacitor. Nothing in the 160m circuit is connected when it's on 10m. The
>> tubes also get extra warm in the 10m position.
>
>This is apparently a common problem on SB1000/AL80 type amplifiers.  My 
>SB1000 bandswitch was damaged in this way.  What happens is that the 
stationary 
>contactof the bandswitch (which happens to be close to the frame) is 
connected to the
>tube plate, and the moving contact goes to the capacitor.  Because the fixed
>contact is quite 'pointy', there is a very high potential gradient at the 
>tip of it, and it tends to arc.  
>
>The solution suggested to me here (and used in some of the later models of 
>this amp) was to place a 3/8" diameter washer over the stationary contact and 
>
>solder it there.  It is important that the washer be polished and all sharp 
>points on the stationary contact where the wire is soldered to it be 
smoothed.  This
>"corona washer" reduces the potential gradient at the tip of the contact.
>
>I did this and have had no further problems.  In my new amplifier, I'm 
>using a much better bandswitch.  The ones in the SB200/220/1000 and AL80 
series are
>really pretty marginal.
>
?  The bandswitches used in the AL-80, SB-220 and SB-1000 are similar and 
have a measured breakdown potential of over 5500v.  The actual tank piv 
in these amplifiers is around 3000v when the tank is tuned to resonance 
and loaded for max. P out.  When the tank is tuned out of resonance, less 
peak V appears across the bandswitch and Tune C.   //  Photographs of 
arced AL-80 and AL-82 bandswitches may be seen on my Web site.  

-  Later, Vic


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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