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 contact
of 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.
73,
Vic, K2VCO
Fresno CA
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