[Amps] Amps Digest, Vol 166, Issue 26, reference direction of current flow in screen grids

[N1BUG]

On 10/26/2016 03:39 PM, Gene May wrote:
> Suggestions by Bill and Gary K4FMX and others to put a resistor
> from the screen to the cathode, such that the resistor will pass
> at least the maximum "negative current" (meaning the screen is
> emitting electrons) that the screen will pass will work fine.
> This is absolutely essential if the screen grid supply is series
> regulated.

Agreed. Eimac mentions this in the tube data sheet. The reason many 
of us don't like this is that it makes the screen current meter 
always read some amount of current when the tube is doing nothing. 
It can be compensated for, but that adds complexity.

>  Zeners connected in this way (a way to parallel
> regulate the supply) should pass at least the same.

In the (old) data sheet, Eimac states that a shunt regulator using 
VR tubes is fine and does not need the resistor from screen to 
cathode. My presumption is the same holds for a shunt zener diode 
regulator. But even after all the discussion here and a more or less 
consensus on that, I still wish I better understood what actually 
happens in the circuit under conditions where electrons are flowing 
*out* of the screen. It's academic, really. I don't need to 
understand how and why it does what it does in order to make it work.

> Suggest finding a copy of the Eimac publication Care and Feeding
> of Power Grid Tubes, out of print but easy to find used online
> from used book dealers or at hamfests.

Good idea. I see there were several editions. I wonder how much 
changed through the years?

73,
Paul N1BUG