>
>
>On Mon, 28 Jan 2002 16:46:29 -0800 rich <2@mail.vcnet.com> writes:
>
><snip>
>
>> >>- 1N5357 5W, 20V, DO-5 case zeners currently cost 80-cents US each
>at
>> >>Digi-Key. 20 would be needed for a 4cx250R supply - 18 for a
>4cx250B
>> >>supply. The safe current carrying ability is c. 85mA - which enough
>for
>> >>8, 4cx250s in linear service.
>
>> - R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
>
>Hi Rich,
> Well, it may be cute to tile a vectorboard with those but, it isn't
>economic at $16.
>
> A suitable power FET costs a $1 these days. Add another $1 for a
>voltage regulator IC and a few small R's & C's.
- To ice the cake, one still needs a similar 400v zener string to protect
the FET from Drain/Source breakdown. As I recall 500V C-E FETs go for a
bit more than $1. Such a device also needs a heatsink.
>Get fancy, add a trimpot
>for voltage adjust so you have "something to turn" and you have a $3
>regulator.
>
- And, as an added bonus, one has a high current-gain IC in an RF
environment.
- I built the 2, 4cx250R 2m linear amplifier with the ancient
Eimac-recommended screen shunt-reg. circuit (powered from the anode
supply) 25 years ago. It has not yet failed or failed to protect the
tubes. Sometimes mo' tricky is not mo' betta.
cheers, Marv
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
end
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