From: <[EMAIL PROTECTED]>
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
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