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[Amps] SB-220 Bandswitching

Subject: [Amps] SB-220 Bandswitching
From: W2RU - Bud Hippisley <>
Date: Sun, 04 Jun 2006 11:37:26 +0000
List-post: <>
Peter Chadwick wrote:
> In my innocence, something puzzles me. Is the indexing on the SB220 
> bandswitch very weak, or are the capacitors very stiff?
In my opinion, the former is true -- on *my* SB-220, at least.

>  I would have thought that the resistance to turning of the bandswitch would 
> be sufficient to tell the operator that he (or she) was attempting to turn 
> the wrong knob before it actually moved.
Peter, I think the problem is compounded by the fact that there's some 
initial "stiction" when first trying to turn the capacitors.  I just did 
some experimenting in response to your posting, and I find the force 
needed to get the capacitors to start moving is extremely similar to the 
force needed to turn the bandswitch -- especially if the capacitors 
haven't been turned recently. 

Also, when operating a contest and/or suffering from lack of sleep, 
there may be no rational reason for turning the wrong knob -- just a 
"foggy" head doing dumb stuff.  In my shack, the amplifiers are off to 
the side so that I'm seldom looking in that direction "in the heat of 
> What size is the bandswitch? Is it the one with centres about an inch and a 
> quarter apart? If so, it's pretty marginal at 1 kW: the KW1000 amp from KW 
> Electronics in the UK used that size switch, but had a phenolic shaft to get 
> the voltage rating up.
Sorry -- can't help with answers to those questions.  However, I *will* 
say that my SB-220 seems to have too *little* bandswitch detent 
resistance whereas my Amp Supply LK-550 has too *much*.  In fact, I can 
envision a time later in my life when arthritis or gradual infirmity 
will make it impossible for me to change bands on the Amp Supply unless 
I add some mechanical advantage to the present knob or wait for the home 
health aide to arrive... :-) .

Bud, W2RU
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