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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