[Amps] small transformer evaluation AND POWER SUPPLY FOR SCREEN GRIDS

[Gene May]

REPLY TO THE REPLY:  Yes, it is true that:  "it is a current regulator, not a voltage regulator".  That would be why it should be shunt regulated in this application, with total current through the active part of the shunt regulator and bleeder resistors while the tube is idling that is at least equal to the highest value of "reverse current" from the screen.
 
I hope we don't get involved and confused with the "which-way-do-the-current-and-electrons-flow" thread also going on now; in what follows, I discuss electron flow.  I think ALCON with this thread will agree with the following:  Screen current can do seemingly weird things while electrons are flowing by it enroute to the plate.  At some levels of electron flow to the plate and values of plate voltage, more electrons can get "knocked off" a screen than are intercepted by it.  This will play havoc with voltage regulation at the screen if the power supply for the screen isn't designed to manage this situation.  Series regulated screen supplies, whether choke or capacitor input, often do not deal well with their load (in this case, the screen) trying to force electrons back into them.  It is particularly important that they be bled suffficiently so that they never see this reverse electron flow.  Another reason to shunt regulate screen power supplies.
 
Gene  WB8WKU 
 

> From: dezrat1242 at yahoo.com
> To: amps at contesting.com
> Date: Wed, 5 Sep 2012 08:28:45 -0700
> Subject: Re: [Amps] small transformer evaluation AND POWER SUPPLY FOR SCREEN GRIDS
> 
> ORIGINAL MESSAGE: 
> On Tue, 4 Sep 2012 20:45:18 -0400, Gene wrote:
> 
> >. I like choke input filters because if the choke is big enough (has "critical inductance"), it acts as a passive regulator by itself. 
> 
> REPLY: 
> A choke does indeed act as a regulator, but it is a current regulator, not a voltage regulator. Exactly the wrong thing for a screen supply. 
> 
> 73, Bill W6WRT
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