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Re: [Amps] tetrode reverse screen grid current

To: "Ian White GM3SEK" <gm3sek@ifwtech.co.uk>
Subject: Re: [Amps] tetrode reverse screen grid current
From: "Hsu" <hsu4qro@gmail.com>
Date: Mon, 30 Jan 2012 08:44:34 +0800
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Hi Ian,
    This ia my thought , just a sketch, you can look it here: 
http://www.zmdz.com/bbs/incomefiles/20121/307105514796.JPG
The top schematic is the traditional series regulator screen power supply.
The bottom's is what  I descript: the  dashed rounded is what I added shunt 
regunlator.
  Yes ,It  we have doubled the circuit complexity, But I do not think it is 
complex  to much, and I do not think protect these device and the tube 
/socket's cap  is how diffcult thing.
  we need adjust carefully the  shunt regulator let it active when the 
screen voltage upward  , if two regulators out put  voltage  near 
equality( the shunt regulaton needs higher a bit, just only a bit, manybe 
0.2,0.1 even 0.05V, jusk only keep block diode turn off).so I do not think 
it will have problem in SSB vocie servoce whe switch from series/shunt 
regulator eachother, if we  optimize  the speed of response of two 
regulators.
Certainly , the pure shunt regunlator is perfect for the tube , but low 
efficiency.mine just a  compromise, its performance should near pure shunt 
regulator but much better better than  series power supply +diode+bleeder 
restistor .
    73!Hsu


-----原始邮件----- 
From: Ian White GM3SEK
Sent: Monday, January 30, 2012 3:56 AM
To: amps@contesting.com
Subject: Re: [Amps] tetrode reverse screen grid current

Hsu wrote:
>  Maybe I can not  describ it clearly. Sorry for my bad English.

Don't worry, your English is fine, but sometimes we all need to use more
words  :-)


>I have read your article and the manuals carefully many  years ago,
>very good job!
>But I do not think it can use my 4CX5000R project othewise modify the
>screen shunt power supply  greatly.
>The shun regulater with low   efficiency although it  can hold negative
>screen current,So I do not think pure shunt regulator in big amp( l
>4CX5000/10000/15000) is good option

A shunt regulator is probably the best solution for tetrodes up to the
4CX1000-1500W class, but for larger tube like the 4CX5000 or 4CX10,000
the shunt circuit consumes a lot of DC power, so we have to look for
something more efficient.

>.but series  rugulator cann't hold  negative screen current, if we use
>series power supply for
>secreen power supply , we have to put  a HV block diode and a  shunt
>bleeder resistor ,  when the negative current happened, the block diode
>is turned off and the powewr supply  output current is zero and
>negative current gos along
>bleeder resistor  to ground, in this condition, the screen voltage   is
>not regulated. If  we combine a shunt regulator in a series
>rugunlator's outpuyt ( use a smaller   bleeder resistor
>series a HV MOSFET  as a shunt regunlator), when the negative current
>happened, if the screen voltage gos high, and over series regulator's
>out put  a bit( I assume is 0.2V, as less as possible,just  only keep
>the block diode  turn off) the shunt rugunlator will be  active.
>In this condition, screen voltage still regulated. in postitive current
>condition, only series regulator work, the shunt regulator will not
>active.
> Is It a good idea?

I agree with that analysis - a series/shunt regulator will decrease the
power dissipation in the screen supply... but there is a price to pay.

Instead of one regulator circuit, we now have two, so we have doubled
the circuit complexity. It may not be easy to guarantee a smooth
handover between the two regulator circuits under dynamically changing
conditions such as SSB.

Also, any screen regulator circuit MUST be able to survive a direct HV
arc from anode to screen. The screen supply MUST protect the tube and
the socket (with the often-fragile screen bypass capacitor) and of
course the power supply must protect itself. By "protect", I mean shut
everything down without damage, and then come back online with a press
of the Reset button.

That isn't easily done.

>I have find  many commerical broadcasting transmitter's screen power
>supply's design, most of them use series regunlator+block diode+ shunt
>bleeder resistor. It is not perfect.

No, it isn't... at that power level, nothing is.

>I 'm studyig Racal's design now, it is unique.

Details, please?


-- 

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek
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