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[AMPS] SB-220 Smoke Test

To: <amps@contesting.com>
Subject: [AMPS] SB-220 Smoke Test
From: 2@vc.net (measures)
Date: Wed, 27 Sep 2000 10:35:43 -0700
>
>measures wrote:
>>>
>>>Did you actually mean to say VLF parasitics?
>>>
>>?  Just how this is possible is somewhat less than obvious.   
>
>VLF resonances are *the* main cause of parasitic oscillation in VHF/UHF
>power amps. 

[chortle]

>They generally arise because half-wave tuned lines become
>open-circuits at low frequencies, so that both the input and output of
>the tube are unloaded. There are then possibilities for oscillation due
>to unwanted resonances between RF bypass capacitors and lead inductances
>or RFCs in the power supply and bias circuits. Another useful function
>of the "glitch resistor" is to damp any such resonances in the B+
>circuit.
>
>Returning to the SB-220 and similar amps, what is the parallel resonant
>frequency of the grid bypass cap and the RFC? Whatever it is, the grid
>is totally ungrounded to RF at that frequency.
>
In the Rauchian world of alleged VLF oscillations, one ignores the 
reactance of C-anode/cathode at VLF.  

end

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


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