[AMPS] MLA2500 and screen voltage for 4CX800.

[Douglas Snowden]

I remember now  why I first mentioned the zener diode string
method.  I used the idea from measures web page on a pair
of 4CX250's on HF.  It worked fine, although I never did any
measurements for regulation.  I do remember that there was
some heat generated though.  I think I used some 5W 36volt
zeners.  

Doug N4IJ
 





measures wrote:
> 
> >
> >
> >> Hi Douglas this is a very bad idea. The IMD performance of any tetrode
> >> is dependant on good screen voltage regulation. The dynamic regulation
> >
> >
> >That 's true.
> >
> With good quality zeners, the screen regulation is ok.  Cheap zeners are
> not a bargain.
> 
> >> of the plate supply is pretty bad and this obviously causes problems
> >> with screen regulation if a string of zeners are used.
> >
> >Why? There is no reason it should cause problems if you wrap
> >around the zeners with few transistors.
> >
> >The series resistance of a string of zeners might be too large
> >compared to the dynamic resistance of the screen, but if you have
> >enough voltage feeding the shunt regulator (at least twice the
> >screen voltage under full load) to properly current limit the screen
> >the zeners won't waddle around enough to hurt.
> >
> >Just don't use zeners as the shunting device. Use some transistors
> >so the current gain lowers the shunt impedance. That way you can
> >use low power zeners, and regulation is good.
> >
> Unsliced bologna.  A string of 5w / 20v zeners can handle anything up to
> a pair of 4-400Cs (800v).
> >
> >
> >
> >
> >
> >
> >
> >
> >John Nelson
> >> GW4FRX wrote some excellent articles on this in the 80s.John frequents
> >> this forum so he may wish to comment.Meanwhile try this link for a
> >> solution http://www.ifwtech.com/g3sek/boards/tetrode/tetrode-1.htm and
> >> some background info.
> >>
> >> Regards
> >>
> >> Conrad Farlow G0RUZ
> >>
> >>
> >> --









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> >>
> >
> >
> >73, Tom W8JI
> >W8JI@contesting.com
> >
> >--
> >FAQ on WWW:               http://www.contesting.com/FAQ/amps
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> >
> >
> 
> -  Rich..., 805.386.3734, www.vcnet.com/measures.
> end
> 
> --
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-- 
	Doug Snowden
       Systems Branch
National Climatic Data Center
  Asheville, North Carolina

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