[Amps] 4CX250B Screen Supplies

[R.Measures]

On Jul 19, 2004, at 8:45 PM, Will Matney wrote:

> Since some have been discussing the 4CX250B supply voltages and the 
> regulation thereof, I figured it would be worth mentioning older ways. 
> Matter of fact, this older way is tougher than zener diode strings. 
> There is still available in good quantity gaseous regulator tubes 
> still being made. Typically used ones were the OA2 and OB2. The OA2 is 
> a 150 volt regulator, and the OB2 a 105 volt. Two OA2 tubes in series 
> would get you right at +300 Vdc for the screen supply. I have also 
> seen three OB2's in series for this getting 315 Vdc. They fit a 
> standard 7 pin miniature socket which is still being made. These are 
> tough as a Abrams tank and don't short easily like zeners could. Keep 
> in mind that the voltage can be made adjustable by placing a 
> potentiometer between the last tube and ground just like zeners.

This is guaranteed to spoil dynamic regulation, both with zeners and 
with gas regulators.  The caveat with zeners is, except in Antartica, 
don't run them at more than 1/3 of their dissipation rating.  //  The 
easiest way to make a zener string adjustable is to make the tap 
movable.

 >
> The formula for the dropping resistor is Es - Er / I . Es is the 
> source voltage, Er is the regulated voltage, and I is the tube current 
> which is usually 40 mA (0.04 amps). I used some 325 Vac transformers I 
> have here (the ones for sell) to do this easily in the past. These can 
> regulate a negative circuit by simply changing the cathode and anode 
> around like a diode. Sometimes tubes just beat semiconductors when 
> power handling is evolved. I think they are being made in China by 1-2 
> manufacturers along with the sockets. Use a varistor rated at 30-50% 
> of the screen voltage with the tubes parallel to ground to clamp any 
> over voltages-spikes.
>
> Will Matney
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org