>
>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
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|