I believe it has been suggested before on amps that it's a good idea to replace
the bandswitch knob on the SB-220 with one that is very different from the two
capacitors - maybe a large bar knob, for example - as an aid in avoiding 4AM
problems.
73, Pete N4ZR
At 07:37 AM 6/4/2006, W2RU - Bud Hippisley wrote:
>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
>battle".
>.
>> 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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