[AMPS] parasitic suppressors

[Rich Measures]

>
>On Tue, 9 Dec 97 18:24:56 -0800 Rich Measures <measures@vc.net> writes:
>>>
>>>On Mon, 8 Dec 97 20:00:24 -0800 Rich Measures <measures@vc.net> 
>>writes:
>>>SNIPS
>>>I AM suggesting that 1500W of 28MHz RF from any amp will seriously heat
>>>up a #16 CU wire from the plate cap thru to the top of the Tune cap. 
>>>I suspect that you could understand why if you stopped your hyperbole long
>>>enough to study it. 
>>>Dick, Tom, Ian and others I believe have covered this ages ago. 
>
>>RG58/u is rated at roughly 600w at 28MHz -- which works out to 2.3A.  
>
>The actual ratings of RG58A/U is 650W at 10 MHz  not 10M. At 50 MHz it is
>250W. But that has nothing to do with the discussion.
>You must have been taking dancing lessons from another.....
>
I did the math.  
>
>>As I recall, the center conductor of RG58/u is quite a bit smaller than 
>>#16 -- like maybe #19.  If 1A will "seriously heat up #16 gauge Cu", why 
>>doesn't 2.3A seriously heat up #19 (or so) gauge copper?  
>>-  At 25A/60Hz, #16 gauge Cu gets seriously warm in free air.  Does it make sense that
>> 1A at 28MHz could do essentially the same thing?  
>
>
>Why dont you just try it and find out. 
>  Replace all the plate wiring and
>strap in your SB-220 and key down for several minutes.
>
I don't need to try Cold Fusion to know that it's a delusion.  
-  1A at 28Mhz in #16 gauge Cu,, generating serious heat?  Give us a break.  And besides that, if Ls was cookin' Rs, it would leave barbeque grill marks on Rs, which it does not. 
,,, ,,, 
... ... 
>>One SB-220 owner told me that he took the 220  to work and put a probe 
>>from a spectrum analyzer through the perforated cover of the output 
>>compartment.  The signal was 50wpm CW dits.  He said he could see the 
>>damped-wave ringing at c. 110MHz at the beginning and ending of each 
>>dit, and whenever the amp. was keyed or unkeyed with zero signal drive.  
>
>And replacing the possibly overheated and overvalue 47 Ohm 2W carbon
>cured it ??
>There should have also been grid current flickering when it was zero
>drive keyed if the parasitic was that pronounced as to always be there. 

>It would not suprise me that a slight change in the L spacing on the
>resistor would have altered the analyzer picture. Did your owner take his
>tests thru to a cure or conclusion?
>
No.   Damped ringing is not regenerative.  Damped ringing will always be there whenever the anode current changes, no matter how low the VHF-Rp of the suppressor happens to be.  .  

>Too bad; but that is still just a minor parasite....

€  no parasite, just damped ringing of an L-C resonant circuit.  

>I asked about a Big
>Bang analyzer picture. Or do you find those dancing shoes moving again?

One would need a memory-type spectrum analyzer to lay in wait for the Big Bang.  Most stock amplifiers never ever have a big bang.  
... ... 
>The Big Bang will generate tremendous amounts of RF, at that instant, of
>unknown frequencies. Zeners and the like do not handle that very well. 

-   The current path from the alleged anode/grid vanishing-gas arc is not through the bias zener.  However, with a parasitic oscillation, the fault current path would be through the bias zener.  

>It
>does not have to be in the direct path if the wiring is saturated with it
>and in the SB-220 at least the Zener protrudes into the RF cavity.  

It might be interesting to measure the C between the chassis and the zener diode stud that protrudes in the RF cavity.  

>> The voltage drop across this amount of R would be 2.4v peak -- which 
>>equals 0.06w peak in a 100 ohm Rs.  
>
>That assumes a DC path only. If the L in the suppressor is acting as a
>RFC then the R takes all the gaff or in actuality the load is somewhat
>shared assuming an imperfect RFC.

This L is only 0.09uH.  With a DC pulse?, hardly.  With a 110MHz regeneration, possibly.  

cheers
Rich...

R. L. Measures, 805-386-3734, AG6K   


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