> ? In the DAF circuit, it seems to me that there is no RF neg. feedback.
> Am I missing something, Tom?
Yes, or maybe I am.
The G2DAF circuits I've seen might have been modifications of the
original design, but they were all cathode driven with screen voltage
robbed off the exciter power.
All cathode driven amplifiers have negative feedback, because the
input is in series with the output. The same current flows through
both.
The feedback is set by the ratio of anode load impedance to
cathode driving impedance. The smaller the impedance ratios, the
more the negative feedback.
Of course none of that applies to a grid driven PA, unless you add
an RF friendly cathode resistance to induce the same type
feedback.
> >I've seen that in measurements here. However,
> >the same tube has ALWAYS been cleaner with the DAF circuit
> >disconnected in tests I've made.
> >
> >I should also point out I can get good IMD performance at one drive level
> >with a class C power amp, if I carefully tune it.
>
> ? However, there are infinite drive levels with voice modulation. .
That's one reason why a fixed level two tone test is a poor indicator
of voice performance in an amplifier, especially one with imperfect
power supplies and biasing.
73, Tom W8JI
w8ji@contesting.com
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