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[AMPS] Screen regulator circuit needed

To: <amps@contesting.com>
Subject: [AMPS] Screen regulator circuit needed
From: John Fielding" <johnf@futurenet.co.za (John Fielding)
Date: Sun, 15 Nov 1998 18:20:33 +0200
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Series pass stabilisers do not absorb the negative screen current that =
tetrodes typically generate.  Using a series pass stabiliser causes the =
screen voltage to go up and down in sympathy with the negative and =
positive screen current, which can cause the tube to flash-over with =
spectacular results!

The only safe screen stabiliser is a shunt stabiliser.  This can be made =
using either mosfet's or bipolar's, the tv industry has some good =
(cheap) devices which can safely handle 1500V.  Today the tube shunt =
stabiliser is a bit of an oddity, but they can still be made to work, =
but transistors are a better choice.

John    ZS5JF
-----Original Message-----
    From: Rich Measures <measures@vc.net>
    To: Bill Coleman <n2bc@ibm.net>; amps@contesting.com =
<amps@contesting.com>
To: <amps@contesting.com>
    Date: Sunday, November 15, 1998 3:34 PM
    Subject: Re: [AMPS] Screen regulator circuit needed
   =20
   =20
   =20
    >
    >I'm wrestling with trying to get a couple of 811s and a string of =
VR tubes
    >working as a regulator on a 1KV screen supply for a 4-1000 in AB1 =
(early 60s
    >handbook circuit).=20
   =20
    =80  One needs triodes with a Mu of under 5 for pass regulator =
service.  .
   =20
    >I picked this circuit because I had the 811s. So far I've
    >succeeded in building a nifty 200W or so LF oscillator (big =
surprise).
    >
    >I've looked at the G3SEK circuit & Ian says it won't stretch to =
1KV.  I have
    >a couple of other circuits I could try but I'm without a handy =
supply of low
    >mu triodes (60s vintage handbook ckts).
    >
    >Anybody have any pointers to other circuits or articles?  ....
   =20
    =80  Bipolar transistors have a secondary-breakdown problem which =
makes=20
    them problematic in HV pass regulator service.  Power FETs are =
virtually=20
    immune to secondary-breakdown.  .  From my experiences, National=20
    Semiconductor's 723-based "positive floating regulator" circuit =
(using=20
    FET pass transistors) is good for regulating screen potentials.    =
2000v=20
    regulated output is practical with 600v-rated FET pass transistors.  =
 =20
    Since FETs operate with zero gate current, paralleling FETs for more =

    current is easy.  .  On my Web site, there is a diagram and an =
article=20
    about this regulator.   My version of National's  "positive floating =

    regulator" circuit is short-circuit proof and RF proof. =20
    -  later, Bill.
   =20
    Rich. Measures.,www.vcnet.com/measures, 805.386.3734
   =20
   =20
    --
    FAQ on WWW:               http://www.contesting.com/ampfaq.html
    Submissions:              amps@contesting.com
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   =20

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<DIV><FONT color=3D#000000 size=3D2>Series pass stabilisers do not =
absorb the=20
negative screen current that tetrodes typically generate.&nbsp; Using a =
series=20
pass stabiliser causes the screen voltage to go up and down in sympathy =
with the=20
negative and positive screen current, which can cause the tube to =
flash-over=20
with spectacular results!</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>The only safe screen stabiliser is a shunt =
stabiliser.&nbsp;=20
This can be made using either mosfet's or bipolar's, the tv industry has =
some=20
good (cheap) devices which can safely handle 1500V.&nbsp; Today the tube =
shunt=20
stabiliser is a bit of an oddity, but they can still be made to work, =
but=20
transistors are a better choice.</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>John&nbsp;&nbsp;&nbsp; ZS5JF</FONT></DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 solid 2px; MARGIN-LEFT: 5px; PADDING-LEFT: =
5px">
    <DIV><FONT face=3DArial size=3D2><B>-----Original =
Message-----</B><BR><B>From:=20
    </B>Rich Measures &lt;<A=20
    href=3D"mailto:measures@vc.net";>measures@vc.net</A>&gt;<BR><B>To: =
</B>Bill=20
    Coleman &lt;<A href=3D"mailto:n2bc@ibm.net";>n2bc@ibm.net</A>&gt;; <A =

    href=3D"mailto:amps@contesting.com";>amps@contesting.com</A> &lt;<A=20
    =
href=3D"mailto:amps@contesting.com";>amps@contesting.com</A>&gt;<BR><B>Dat=
e:=20
    </B>Sunday, November 15, 1998 3:34 PM<BR><B>Subject: </B>Re: [AMPS] =
Screen=20
    regulator circuit needed<BR><BR></DIV></FONT><BR>&gt;<BR>&gt;I'm =
wrestling=20
    with trying to get a couple of 811s and a string of VR =
tubes<BR>&gt;working=20
    as a regulator on a 1KV screen supply for a 4-1000 in AB1 (early=20
    60s<BR>&gt;handbook circuit). <BR><BR>=80&nbsp; One needs triodes =
with a Mu of=20
    under 5 for pass regulator service.&nbsp; .<BR><BR>&gt;I picked this =
circuit=20
    because I had the 811s. So far I've<BR>&gt;succeeded in building a =
nifty=20
    200W or so LF oscillator (big surprise).<BR>&gt;<BR>&gt;I've looked =
at the=20
    G3SEK circuit &amp; Ian says it won't stretch to 1KV.&nbsp; I =
have<BR>&gt;a=20
    couple of other circuits I could try but I'm without a handy supply =
of=20
    low<BR>&gt;mu triodes (60s vintage handbook =
ckts).<BR>&gt;<BR>&gt;Anybody=20
    have any pointers to other circuits or articles?&nbsp; =
....<BR><BR>=80&nbsp;=20
    Bipolar transistors have a secondary-breakdown problem which makes =
<BR>them=20
    problematic in HV pass regulator service.&nbsp; Power FETs are =
virtually=20
    <BR>immune to secondary-breakdown.&nbsp; .&nbsp; From my =
experiences,=20
    National <BR>Semiconductor's 723-based &quot;positive floating=20
    regulator&quot; circuit (using <BR>FET pass transistors) is good for =

    regulating screen potentials.&nbsp;&nbsp;&nbsp; 2000v <BR>regulated =
output=20
    is practical with 600v-rated FET pass transistors.&nbsp;&nbsp;&nbsp; =

    <BR>Since FETs operate with zero gate current, paralleling FETs for =
more=20
    <BR>current is easy.&nbsp; .&nbsp; On my Web site, there is a =
diagram and an=20
    article <BR>about this regulator.&nbsp;&nbsp; My version of =
National's&nbsp;=20
    &quot;positive floating <BR>regulator&quot; circuit is short-circuit =
proof=20
    and RF proof.&nbsp; <BR>-&nbsp; later, Bill.<BR><BR>Rich.=20
    Measures.,www.vcnet.com/measures, 805.386.3734<BR><BR><BR>--<BR>FAQ =
on=20
    =
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