>
>Gents,
>
>Here is a re-send of my last post with a corrected and more relevant
>subject heading. Apologies for the wasted cyberspace.
>
>73 Graham VK3BKG,
>
>
>G'day Carl,
>
> In reply to Greg's query on loading, you wrote:
>
> > Loading Heavy actually means to DECREASE the Load C value, it is
> > confusing. On top of that the 0-100 panel labeling is one way on some
> > amps and the opposite on others.
> >
> > I prefer to tune for absolute max on the Bird and then increase loading
>(
> > Less C-2) until power drops about 5%. This will be the point of best
>IMD.
> > Any reduction in power should then be done at the exciter. A MLA with
> > perfect tubes is capable of over 1500W out @ 100W drive but that is
> > really pushing them.
> >
> > 73 Carl KM1H
> >
>
> I've been curious about a related subject for a while. I believe I more
> or
> less understand the mechanism by which heavy plate loading reduces IMD
> (i.e. by limiting negative peak anode voltage excursions going into the
> non-linear region).
? agreed
>But how does it increase tube life?
? I do not see how it could. In the 8873/4/5s I've autopsied I saw
cathodes destroyed by operators who exceeded Eimac's 350mA max. AØ
rating. This is typically accomplished by using more than the
recommended 27w of drive per cathode. (photo of destructed cathode in
"Parasitics Revisited" Sept./Oct. 1990, *QST*) . . . Does heavy
loading reduce cathode current?.
- later, Graham
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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