[AMPS] Another arc question

[Ian White, G3SEK]

Carl wrote:

>>As the words "series" and "trap" are normally used, that would imply
>>that the suppressor is resonant
>
>Wrong choice of words on my part Ian. But since the L is self resonant at
>some point would this not be a consideration?  After all it is simply a
>RFC with a Q damping resistor across it. No different IMO than the old
>grid bias choke-resistor combination from ancient Class C days. In fact
>Heath uses the same combination in the SB-200 bias circuit.
>
>The L in a SB-220 suppressor shows a self resonance of 210 MHz on my
>trusty old Measurements 59 GDO. 

 ...which is borne out by N7WS's measurements (and maybe it was a vector
impedance analyser, not a network analyser). As I said:

>>
>>Check the graph of measured Q from N7WS. On a log-log plot, the 
>>classic
>>LR suppressor gives an almost straight sloping line (just as it 
>>should)
>>with absolutely no sign of resonance effects below 200MHz where the
>>measurements stopped.
>
>But the L and the R are critical and one size does not fit all tubes or
>even the same tube in all layouts.
[brief snip]
>So therefore that sloping line plot you mentioned must be
>shifted to place the attenuation where it is needed.

Yes, we agree on that.

>>
>>The nichrome suppressor has significant losses in the inductor as well
>>as in the resistor. That's the only difference. The question is 
>>whether
>>this is an advantage or not...
>
>I believe it has an advantage where the parasitic is not sufficiently
>suppressed in the original network. It makes it easier for "Joe Sixpack"
>who has neither the knowledge or equipment to design his own.
>
 We agree on that, too.


>One thing that this discussion must make clear is that you can not lump
>all of the failure events under one heading. You have gas, parasitic
>resonances in the tube and VHF/UHF resonances in the tank circuit. Three
>completely seperate issues that have to be addressed individually....even
>though there certainly may be interactions. Thats what make amplifiers
>fun.

Carl, we'll have to stop agreeing like this! People will begin to talk.

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)
                           http://www.ifwtech.demon.co.uk/g3sek

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