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). But how does it increase tube life? The Eimac data
sheet for the 4CX250B states in regard to VHF operation: "Such operation
should be conducted with heavy plate loading, minimum bias, and the lowest
driving power consistent with satisfactory performance. It is often
preferable to operate at a sacrifice in efficiency to obtain increased
tube
life."
To Carl and other knowledgable persons on the reflector - could you
please
explain how heavy plate loading and reduced efficiency can increase tube
life.
I apologise if this subject has been covered previously on the reflector.
Thanks in advance.
73 Graham VK3BKG
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