Hi Marv,
> In fairness to the DAF design, wouldn't it be more appropriate to tell us
> WHAT tube(s) were employed in the amps for which the IMD was quoted and
> what was the IMD of the exciter? Many years ago, I was privileged to see
> IMD test data on the 813 tube that was taken by a major manufacturer of
> power tubes.
High driving impedance tubes, like the 813, traditionally do better
when used in the DAF circuit than what are normally considered
"good" tubes with low driving impedance.
That's because the large amount of negative feedback cancels
some of the IMD. 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. It depends on
what we accept as a standard. I've seen class C amps do in the
high -20 dB range in two tone tests. Darned if I want someone loud
using one of them, most rigs are bad enough.
73, Tom W8JI
w8ji@contesting.com
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