Il 16/01/2011 19.19, Antonio Vernucci ha scritto:
I am planning to build a suppressor-grid modulated AM transmitter.

In all the diagrams I have seen they use proper pentodes, i.e. tubes
that have a real suppressor grid (e.g. 803).

I have seen no diagram using beam power tubes (e.g. 813 or 814) which
have beam forming plates instead of the suppressor grid .

Before purchasing 803 tubes, I would like to be sure that 813s or 814s
are really unsuitable for suppressor-grid modulation.

My question is whether, with 813s or 814s, the plate current can be
actually controlled by varying the beam forming plates voltage.

Does anyone have experience on that issue?

73

Tony I0JX

Rome, Italy


Hello Tony, de Piero I5SPO.

Quite a ( very ) long time ago, i've done an A.M. TX with a
Geloso VFO and a class C RL12P35 Wehrmacht pentode, whose
characteristics are similar to 1625 ( a.k.a. 807 with
12.6 v filament ), using a carbon mike and a step-up
audio transformer.

I believe that, using beam tetrodes, there's no way... :-(

I know also 813 and 814 ( have 2 pcs ) and these, like 807,
are useful for controlled carrier A.M. by modulating screen grid.

Do not know 803, but if i remember well, are low power tubes.

Used with suppressor modulation, their output will be one fourth
of CW rated output, and efficiency is consequently low... :-(

HTH,

73, Piero.