[AMRadio] 807's triode connection question...

[Donald Chester]

>From: <ka1iic at prexar.com>

>Makes sense... but I have the 'feeling' that by connecting a
>pentode/tetrode as a triode you get something other than a triode...
>
>As in none of the above... something 'different'...  with a 'nature' all
>of its own...
>
>Right/wrong???
>73
>Vince

Vince,

In either case, the tube acts as a triode.  By connecting the control and 
screen grids together, you have in effect a single control grid with a lot 
of wire mesh, giving more capture area to the grid, thus making it high mu 
since the combined grids will have a large effect on the electrons flowing 
from cathode to plate.  If the screen is strapped to the plate and the 
control grid is driven in normal fashion, the screen grid becomes part of 
the plate.  Undoubtedly it alters the characteristics somewhat, since the 
effective plate-grid spacing is reduced by the screen grid.  The control 
grid alone has less wire mesh and therefore less effect on electron flow 
than the combination.  Functioning as a triode, the overall gain of the tube 
will be less than it would be connected as a tetrode.  One configuration 
gives you a high-mu triode and the other a low mu triode.

As another example, the tube charts for the type 46 pentode describe it as a 
"triple-grid" tube that can  be connected as a pentode, tetrode, hi-mu 
triode or lo-mu triode, each with vastly different characteristics.

Don K4KYV

_________________________________________________________________
MSN Photos is the easiest way to share and print your photos: 
http://photos.msn.com/support/worldwide.aspx