[ARC5] 12 V Power pentode.

[Kenneth G. Gordon]

On 10 Apr 2016 at 15:27, Arden Allen wrote:

> > Does anyone here know of a power-pentode, which is 1) not a beam-tube, 2)
> > has a 12.6 V filament, and 3) might have an octal base?
> 
> Two tubes immediately come to mind, Dave.  The 12V6 and the 12A6.  But both 
> are beam tubes.  So what's the matter with a beam tube for your application?

It wasn't David who needed it, Arden: it was I. 

And I want such a tube for an ECO VFO in a rig in which all the other tubes have a 12 V 
filament. Also, I am just plain curious if there ever was one.

Beam-tubes do not make very effective ECOs because their construction defeats the 
entire purpose of an ECO. 

In addition, in most cases, what is shown on the tube-base diagram as being a 
screen-grid, is in fact a pair of "beam-forming" plates, 

Trying to use such a tube as an ECO results in the oscilator energy being coupled 
around the "screen" directly to the plate.

In an ECO, the screen grid is supposed to be the "plate" of the oscillator.

As I remember it, the ECO also requires a tube with a suppressor grid, so tetrodes don't 
make good ECOs either: not enough isolation between the oscillator-section and the 
amplifier-section of the tube.

The 6AG7 makes a superb ECO tube, but there isn't a 12AG7. The 12BY7 is also 
excellent in this regard, but it is a 9-pin miniature. Although I could make an adapter for 
this one, I would rather not.

Ken W7EKB