[Amps] Screen Power Supply.

[Carl]

You might want to check out the 2SC3039 and 2SD1398 and see if they fit the 
application. Both are rather robust HV NPN devices that Ive used as 
regulators.

Carl
KM1H


----- Original Message ----- 
From: <gdaught6 at stanford.edu>
To: <amps at contesting.com>
Sent: Sunday, June 29, 2008 10:09 PM
Subject: Re: [Amps] Screen Power Supply.


> 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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