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@yahoo.com
> To: amps@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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