>
>on 11/3/99 09:59, measures at measures@vcnet.com wrote:
>
>> During the Great Debate,
>> there were many stern warnings from critics of "The Nearly Perfect
>> Amplifier" (Jan., 1994 *QST*) - to the effect that manufacturers don't
>> use rheostats to control filament voltage (as per the article) because
>> rheostats simply do not last in this application. The rheostat still
>> works after a dozen years of service.
>>
>WHY? Why would a rheostat stop doing what a rheostat is supposed to do???
>
? Hang onto your hat. The nichrome resistance wire that the rheostat
was made from was subject to disintegration from atmospheric effects.
The graphite contact in the movable arm would crumble. The carbon
contact in the movable arm would wear away quickly. .
>
>> One should keep in mind that above its self-resonant frequency, a
>> capacitor looks like an inductor. For example, your typical 0.01uF
>> disc-ceramic universal "bypass" capacitor looks like an inductor on 20m -
>> 10m.
>
>I agree with your comment. I am surprised though that the caps are that
>poor.
The caps were not poor.
>I know even most "quality RF" caps
Even Quality cap leads have inductance. .
>(mica or otherwise) begin to look
>really bad above 30 MHz, but I am surprised things look bad above 14 MHz.
Perhaps you have not measured the resonance of many caps.
>
cheers, Jon
- Rich..., 805.386.3734, www.vcnet.com/measures.
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