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[AMPS] Re: 6m amp blocking caps

To: <amps@contesting.com>
Subject: [AMPS] Re: 6m amp blocking caps
From: 2@vc.net (2)
Date: Thu, 6 Dec 2001 06:38:16 -0800
>
>2 Wrote:
>
>>//   Do two equal-capacitance paralleled caps have a resonance?
>>
>They do not develop a new parallel resonance due to being connected 
>together.
>
\  This does not appear to be the result when one experimentally 
parallels two, equal value doorknob caps with straps and checks for 
resonance with a dipmeter.

>>And later:
>>//  In my experiences 50, 57, and 58 Series doorknob caps have a
>>resonance at VHF or UHF.  A 0.01uF disc ceramic cap resonates c. 10MHz.
>>
>Certainly - these are all *series* resonances with their self-inductance 
>(plus the inductance of the wire you used to "short" the cap for 
>dipping).
>
>>//  Mr. Rauch stated that the dipmeter adapter does not work correctly.
>>
>I seem to remember he said that MFJ marketed it against his advice 

\  semi-agreed

>- but the MFJ analyzer manuals do give details of the methods I suggested, 
>which are superior to dipping.
>
\  Certainly - for finding the series resonance of a single capacitor.  
This number is important to know since a bypass-C behaves like the 
desired capacitive reactance only below the series resonant freq.   Above 
this point, it looks inductive.  This is why a tetrode-with-handles 
cathode/fil. needs bypasses using different capacitance values.  As I 
recall, I used 4, 1000pF; 4, 3300pF; 4, 4700pF; and 4, 6800pF -- rated 
at3kV.  

>
>>>lMost modern CF/MO resistors have a spiral element, but if you scrape off
>>>the paint, measure the diameter and length, and count the turns, you can
>>>estimate the inductance using the normal coil formula. You'll find that
>>>at low impedance levels the inductance is generally too small to matter
>>>below 30MHz.
>>>
>>//  ... which is about as useful as teats on  a boar.
>>
>I bow to your obviously  extensive knowledge of porcine anatomy... but 
>not to your engineering judgement.
>
\  Touché.  However, the resonance of two, strapped, 58-series doorknob 
caps is not below 30MHz.  As I see it, the resonance of two, paralleled 
DC blocking caps is not often a problem --  although it can be.  I know 
of a 2, 4-1000A/8166 amplifier where it was.  
>
cheerio, Ian

-  R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.  
end


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