Graham Jones wrote:
>I gather that
>recommendations for "heavy plate loading" in the HF region are mainly for
>reduced IMD at the cost of a small sacrifice in efficiency, provided grid
>dissipation is not exceeded. Obviously the term "heavy loading" does not
>mean overloading to the point where efficiency is poor or where grid
>current, anode dissipation or maximum cathode current ratings are exceeded,
>otherwise tube life will be shortened rather than increased. At VHF and UHF
>there may be other significant issues relating to secondary screen emission
>etc.
Another significant issue is that 30 or more years ago, in the period up
to the time when the Eimac application note was written, VHF amps were
notorious for their hit-and-miss output coupling arrangements. These
almost always made the loading being much lighter than it should be -
so perhaps this explains some of the extra emphasis for VHF.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.demon.co.uk/g3sek
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