>
>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.
? In g-g service, 813s are cleaner than most transceivers. The
DAF/813 amplifier I measured had c. -22db of IMD below PEP with voice
modulation.
>
>That's because the large amount of negative feedback cancels
>some of the IMD.
? In the DAF circuit, it seems to me that there is no RF neg. feedback.
Am I missing something, Tom?
>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. .
> 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.
? amen, Tom. However a two-tone test does not produce rapidly
fluctuating screen potential in a DAF amplifier. Human speech is a whole
nuther ballgame.
>
- later, Tom
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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