w3am: Re: [AMPS] Technical Question #1

[Rich Measures]

>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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