[ARC5] Smart People: Triode Connecting Pentodes

[Kenneth G. Gordon]

On 14 Nov 2013 at 16:39, Fuqua, Bill L wrote:

>    I believe by connecting the grids together you produce a high mu
>    zero bias tube.

Yes. According to Bill Orr in a document he wrote for Eimac, connecting the 
grids together results in a hi-mu triode, while connecting the screen to the 
plate results in a low-mu triode.

> 813,803, 4-400, and many others are done this way for grounded grid
> applications.

Yes, but as Bill points out in that article I mentioned, SOME tubes don't work 
well in that condition, while others do. He lists several of each.

> Bill Orr wrote a number of articles on this.

As I said, published in an Eimac document which is available as a PDF on 
line somewhere.
 
>   The down side is that this technique does not work well for class A
> or near class A operation since the grids have to have a positive bias
> on them to get the needed quiescent current.

Makes sense

> And the grid supply has to
> provide considerable current.

Again according to Orr, in tubes such as the 4X150 and 4CX250 family, even 
operating in Class AB2, grid current can be as high as 3 or 4 AMPERES !!!!

>   I once used four 6AG7's in grounded
> grid as an amplifier following my CE 10A. 

I remember that circuit. The CE-20A uses two 6AG7s as linear amps. They 
work well.

Ken W7EKB