-----Original Message-----
From: rich <2@mail.vcnet.com>
To: Steve Thompson <g8gsq@qsl.net>; AMPS <amps@contesting.com>
To: <amps@contesting.com>
Date: 30 January 2002 10:22
Subject: Re: [AMPS] Shunt regulated high voltage psu
>
>
>>
>>
>>-----Original Message-----
>>From: rich <2@mail.vcnet.com>
>>To: Steve Thompson <g8gsq@qsl.net>; AMPS <amps@contesting.com>
To: <amps@contesting.com>
>>Date: 29 January 2002 22:03
>>Subject: Re: [AMPS] Shunt regulated high voltage psu
>>snip
>>>>>There doesn't seem to be any real need for an active series element to
>>>>>feed an active MOSFET shunt regulator. The loop gain in the shunt part
>>>>>is already very high, so the series feed can be just a plain resistor.
>>>>
>>>>Certainly, in that configuration. There's numerous valves where the
>>reverse
>>>>screen current appears to low or non-existent (4CX800 for example),
where
>>>>dumping 40+mA all the time in a shunt regulator feels wasteful.
>>>
>>>// Low screen-V tubes such as the 4cx800 (350V-sc.) suffer more from
>>>reverse screen current than tetrodes with handles. However, even
>>>4cx5000As and 4cx10,000s occasionally exhibit reverse screen current with
>>>1200 - 1500 V on the screen. Bleeding 25mA seems to take care of the
>>>problem.
>>>
>>>>This led me
>>>>to look at series supplies, which led in turn to thoughts about effects
>>>>under fault conditions.
>>>>>
>>>// Did you look at the screen current curves for the 4cx800?
>>
>>
>>Certainly did. The Svetlana data sheet shows no areas of negative screen
>>current, even though the text discusses the need to cater for it.
>>
>// It looks to me like there should be some more curves to the right of
>the 0 screen current line, like there are on the 4cx350 curves.
>Obviously, at times the 800 has negative screen current or they wouldn't
>have mentioned it.
Possibly or probably - I'll find out when I fire one up (anyone out there
save me the bother?). They put -ve contours on the 4CX1600B so maybe they
just cut and pasted the text. Happens all the time - or did when I worked in
the semiconductor business. Anyhow, that's a digression. My guess is that
any -ve current is likely to be small, and normal operation appears to run
around 40mA +ve. It seemed to me to be wasteful dumping 40odd mA all the
time in a shunt just to meet peak demand so I designed a series circuit,
then got to thinking about protection which is where I came in.
Steve
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