>On Wed, 20 May 1998 19:40:12 -0500 bob alexander <realex@flash.net>
>writes:
>>Karl,
>>The main cause of damage to the band switch in the SB220 is
>>Parasitics! These parasitics get into the fingers of the operator
>>who is trying to tune the SB220 and causes him/her to rotate the
>>band switch instead of the loading cap while full drive is applied.
>
>Yup...
>
>A red color insert in the bandswitch knob may help reduce this slightly.
>A different shape knob altogether is a better "non-invasive" solution;
>you'll know you've grabbed the wrong one without looking at it.
>
>A happy (so far) SB-220 beta tester,
>Gary
A different feel/shape knob sounds like a good idea, Bob, however, I have
inadvertently driven my SB-220 when the amplifier was tuned up on another
band. I saw low anode/plate current, presumably because very little
drive was coming through the wrong tuned input pi-network There was
very little indicated RF output. There was no arcing in the Tune-C nor
in the bandswitch. According to some of our recognized amplifier
"experts", I should have been seeing 6000v to 9000v transients in the
tank. The only tank arcing I have seen in the SB-220 was when it was
correctly tuned up and the amplifier was completely stock.
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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