W6TR wrote...
> I've always felt that copying a proven design is more expedient that
> reinventing the proverbial wheel so when I came across George Daughters K6GT
> design for the 4CX1600 amp in the 2000 ARRL handbook, I decided to copy some
> of the circuits he outlined. The power supply looked good to me so I
> started looking up the component parts in my trusty Mouser catalog. When I
> got to the screen supply section, I came across a NPN transistor designated
> as Q1 MPSU010. I cannot find this part listed anywhere. I believe that it
> is manufactured by Central Semiconductor Corp because I see other MPSxxx
> parts made by them but I can't find it on their website. Can someone lead
> me to a source for this part and a description? I am going to take a 300VAC
> Peter Dahl transformer that I found a Dayton a few years back and full wave
> bridge it up to 420VDC and then I want to "regulate" it down to about 350VDC
> with some series Zeners. I am not using the 4CX1600 but that tube seems to
> have a lot in common with the 4CX1500B, the tube I'm going to use.
That darned transistor has generated more correspondence for me than any other
phase of the project! That being so, I'll post to the whole reflector.
Keeping in the mind the fact that the transistor is a series regulating
element, it can
be understood that the key requirements for the (NPN) transistor are:
a. Vce must be greater than the difference between the unregulated voltage and
the
desired regulated voltage... In Bob's case, 420V-350V = 70 Volts minimum. A
150V
transistor would serve well, providing a reasonable safety factor.
b. The beta, or hfe (current gain in common emitter configuration) of the
transistor
does not need to be especially high. Something like 50 at about 50mA of
collector
current is plenty.
c. The power capability required is found by multiplying the Vce by the total
collector current at full load [remembering that there is a constant value of
about
20mA even when the screen grid is not drawing current]. So,
70Vx(.05+.02)mA=4.9Watts, so a 10W or 20W device, mounted on an appropriate
heat sink, should be just fine.
Good luck on the project!
73,
George T Daughters, K6GT
CU in the California QSO Party (CQP)
October 3-4, 2008
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