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[AMPS] Amp opinion/infomation requested ASAP!!

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Subject: [AMPS] Amp opinion/infomation requested ASAP!!
From: g.jones@bom.gov.au (Graham Jones)
Date: Mon, 29 Mar 1999 10:15:04 +1000
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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