[AMPS] Screen regulator circuit needed
John Fielding
John Fielding" <johnf@futurenet.co.za
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>
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
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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. 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> </DIV>
<DIV><FONT size=3D2>The only safe screen stabiliser is a shunt =
stabiliser. =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. 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> </DIV>
<DIV><FONT size=3D2>John 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 <<A=20
href=3D"mailto:measures@vc.net">measures@vc.net</A>><BR><B>To: =
</B>Bill=20
Coleman <<A href=3D"mailto:n2bc@ibm.net">n2bc@ibm.net</A>>; <A =
href=3D"mailto:amps@contesting.com">amps@contesting.com</A> <<A=20
=
href=3D"mailto:amps@contesting.com">amps@contesting.com</A>><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>><BR>>I'm =
wrestling=20
with trying to get a couple of 811s and a string of VR =
tubes<BR>>working=20
as a regulator on a 1KV screen supply for a 4-1000 in AB1 (early=20
60s<BR>>handbook circuit). <BR><BR>=80 One needs triodes =
with a Mu of=20
under 5 for pass regulator service. .<BR><BR>>I picked this =
circuit=20
because I had the 811s. So far I've<BR>>succeeded in building a =
nifty=20
200W or so LF oscillator (big surprise).<BR>><BR>>I've looked =
at the=20
G3SEK circuit & Ian says it won't stretch to 1KV. I =
have<BR>>a=20
couple of other circuits I could try but I'm without a handy supply =
of=20
low<BR>>mu triodes (60s vintage handbook =
ckts).<BR>><BR>>Anybody=20
have any pointers to other circuits or articles? =
....<BR><BR>=80 =20
Bipolar transistors have a secondary-breakdown problem which makes =
<BR>them=20
problematic in HV pass regulator service. Power FETs are =
virtually=20
<BR>immune to secondary-breakdown. . From my =
experiences,=20
National <BR>Semiconductor's 723-based "positive floating=20
regulator" circuit (using <BR>FET pass transistors) is good for =
regulating screen potentials. 2000v <BR>regulated =
output=20
is practical with 600v-rated FET pass transistors. =
<BR>Since FETs operate with zero gate current, paralleling FETs for =
more=20
<BR>current is easy. . On my Web site, there is a =
diagram and an=20
article <BR>about this regulator. My version of =
National's =20
"positive floating <BR>regulator" circuit is short-circuit =
proof=20
and RF proof. <BR>- 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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com/km9p/search.htm</A><BR></BLOCKQUOTE></BODY></HTML>
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