[AMPS] A look underneath the Ugly amp. chassis.

[measures]

>
>on 11/3/99 16:45, measures at measures@vcnet.com wrote:
>
>>> 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.
>
>So according to these "experts" a rheostat is not capable of varying the
>magnitude of an AC voltage.  

... not what they said. 

>Go figure.  Hey, I have a rheostat on my
>filament AND on my HV primary.
> 
A rheostat in the HV transformer primary is bananas.  
>>> 
>>>> 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.
>
>Poor is a relative term.  I mean poor RF performance.  Looking like an
>inductor at 14 MHz may be what is supposed to happen with that cap, but it
>is still "poor" RF performance.

I disagree.  
>> 
>>> I know even most "quality RF" caps
>> 
>> Even Quality cap leads have inductance.
>
>Oh agreed, agreed.  But then that can be minimized by shortening the leads
>as much as possible.  So is the poor 14 MHz performance due to longer leads
>than should be used (sometimes you have no choice) or is the performance due
>to the way the cap is internally constructed?  I'm not disbelieving what you
>measured, I am just trying to get a handle on the HF performance of a
>typical disc capacitor.
>> 
You gotta short the cap with wide Cu foil and measure the resonance with 
a dipmeter..  

cheers, Jon

-  Rich..., 805.386.3734, www.vcnet.com/measures.  


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