Tom said:
..."the fact remains that circuit does about everything you are
not supposed to do with a linear PA. If one or two work, that's fine
with me. But it is not a good design. Because one or two of
something can be made to work doesn't prove it is a repeatable
design, or a good design."
Tom
This is really the essence of the discussion. Let me use a different
example than the "DAF" amplifier.
What would you think about building an vacuum tube oscillator by putting the
high voltage on the control grid. The cicuit could only work because the
electrons attracted to the positive grid but cannot remain there because of
the very small surface area and escape to the plate. The electrons leaving
there strike the less positive plate - causing other electrons to "liberate"
themselves from the plate - going back to the control grid as "secondary"
electrons. Reading further, you learn that most American tubes cannot
tolerate the high grid voltage. So, to use the circuit, you must use a
European tube or a American 24-A.
This circuit would probably fit your description of the "DAF" circuit, since
it represents everything you are not supposed to do with an oscillator.
The oscillator circuit I have described, as strange as it is, is the
dynatron. The description of the circuit is taken from "The Oscillator at
Work" by John Ryder. A few of the advantages of this circuitc are listed by
the author:
1. Excellent frequency stability; oscillator frequency almost completely
independent of changes in operating voltage.
2. Output is an almost pure sine wave. Very low harmonic content.
3. Shifting from one frequency band to another requires the switching of
only one connection.
There are disadvantages to this circuit, and certainly it is not repeatable
using American tubes. But, excellent commercial test equipment was sold
using the dynatron. You might call this circuit design poor engineering.
But, that would be your opinion.
And, you have stated that the design is not repeatable. In fact, there are
two amplifiers shown on the websites previously mentioned. One was a copy
of the other - with the same results. Therefore it is a repeatable design.
Perhaps the "DAF" amplifier is the dynatron or the rf amplifier world. It
is not for everyone. It is not a good design for commercial manufacture.
It is not a good desgin to operate without thorough testing. Remember, the
purpose of these two amplifiers were to satisfy the needs of the operators
and not cause objectionable distortion to others. Based upon that criteria,
the amplifiers are outstanding successes. The owners are quite pleased and
we have not heard one single negative comment from anyone who has critically
listened. If everyone is happy, how can that be a poor design?
Perhaps the only grumbler is someone half way across the world who insists
that it must splatter, even though he cannot hear it.
Colin K7FM
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