>
>
>-----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.
cheers, Steve
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
end
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