I screwed that one up. I was thinking about a series regulator rather than
the shunt zeners. Disregard.
73
Gary K4FMX
> -----Original Message-----
> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Gary
> Schafer
> Sent: Tuesday, October 18, 2016 9:46 PM
> To: 'N1BUG'; 'Amps'
> Subject: Re: [Amps] Negative current with a zener screen grid regulator
>
> Paul,
> With negative screen current the current thru the zener will DECREASE.
> You need to have enough current in the zener string at zero screen
> current
> so it will always be greater than the maximum negative screen current.
> If the negative screen current goes greater than the zener current it
> will
> go out of regulation and the screen voltage will rise.
>
> 73
> Gary K4FMX
>
> > -----Original Message-----
> > From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of N1BUG
> > Sent: Monday, October 17, 2016 2:48 PM
> > To: 'Amps'
> > Subject: [Amps] Negative current with a zener screen grid regulator
> >
> > Hey amp gurus,
> >
> > I have been going around and around with a recently rebuilt VHF
> > amplifier that is refusing to work correctly. To help me think this
> > through, I want to be sure I am understanding how some portions of
> > it are SUPPOSED to work, or the theory of them.
> >
> > I have a 4CX1500B tube. Screen voltage is regulated by a string of
> > five high power zener diodes with the screen voltage tapped at the
> > third or fourth zener from the bottom of the series string. I think
> > I understand how this works with positive screen current but can
> > someone nudge me in the direction of understanding what happens when
> > the tube draws negative screen current? My belief is that current
> > through the zeners (or SOME of them?) INCREASES in by the amount of
> > negative screen grid current.
> >
> > Is that correct?
> >
> > Other than exceeding the power ratings of the diodes, are there any
> > special concerns here? Is there risk of the thing dropping out of
> > regulation and allowing voltage on the screen to rise significantly?
> >
> > I feel sheepish asking this, as I ran this amp for many years with
> > negative screen current and it obviously worked. But now that I'm
> > having problems with it I want to understand things better.
> >
> > I will ask my other question separately as it is not particularly
> > related to this one.
> >
> > Thanks,
> > Paul N1BUG
> > _______________________________________________
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> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>
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