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.

Hi Piero,

the 803 is about the same as the 813, though it has a proper suppressor screen.
Other differences are socket (5 pin vs. 7 pin) and maximum frequency (20 MHz
against 30 MHz).

What I need to know is if any one has ever tried to vary the 813 beam forming
plate voltage, so as to verify whether the plate current can so be controlled.
If so, I could avoid to purchase the 803s and use the 813s I already have.

I know that with suppressor screen modulation output power is about one fourth,
but efficiency will not be so low because, in absence of modulation, also the
input power decreases (by somewhat less than one fourth). With a pair of 803s
(or 813s I hope!) I should obtain about 200W of unmodulated carrier power,
peaking at 800W under 100% modulation.

I used to have a few RL12P35s, though I never actually used them. A Radio
Rivista article by Dante I1DC describes a transmitter using the RL12P50 (a
bigger brother of the RL12P35). But all those tubes are too small for well
exploiting the potential advantages of suppressor screen modulation. As a matter
of fact the advantage of not having to build a powerful modulator becomes more
evident when the needed modulator would be real big!

73

Tony I0JX