Hi Mike and Carl,
I wonder what Carl's amplifier plate current is?
> I would asume the Chinese might have used the Russian
> (AKA Sevetlana)
> design of 572B as their model and they had more gain than
> other mfgrs.
> When Sevetlana first introduced them to the US markets
> it was observed
> that they drove easier to greater output and were (under
> certin
> circumstances and opperating conditions) not too stable at
> the upper HF
> bands necessitating a change in cutoff bias and in some
> cases a change in
> paricitic supressiors and some additinal stabalization
> methods to be
> employed.
The "Svetlana" 572B didn't have any more gain than any other
572 I tested. It actually had a bit less gain. With
Cetron tubes my AL572B puts out just over 1450 watts with
100 watts drive. With Svetlana tubes it outputs about 1300
watts. Some Chinese tubes I tried were pretty good gain.
What the "Svetlana" 572 did have was a little less mu or
some sort of problem where the grid did not cut off the
plate current at idle. With the same cutoff bias voltage it
had more idle current than other brands.
572B's, like 811A's, really have too much feedthrough
capacitance at HF from anode to filament. What would happen
is when the TX relay in the amplifer was released the
Svetlana tubes would not cut off. The antenna and exciter
were removed from the amplifier. With nothing at all loading
the input or the output and with the tube drawing current
there was enough feedback capacitance to make the stage
oscillate at or near the operating frequency.
It would be nice if that mess was a "feature" caused by an
exceptionally good tube, but it wasn't. It was a combination
of a control grid that would not bias the tube off
(generally that means low mu, not higher mu and gain) and
amplifier designs that were not stable to start with.
http://www.w8ji.com/fl2100_problems.htm
It's easy to get gain when an amplifier is on the edge of
stability from regenerative feedback. :-)
73 Tom
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