Rich Measures wrote in reply to G3RZP, who is away from his e-mail for
most/all of next week:
>>Rich, there's a body of opinion that doesn't agree with you. For
>>example, see the curves of IMD against grid volts in The Care and
>>Feeding of Power Grid Tubes. My copy is the third printing,, and it's on
>>page 72. ...snip...
>
>These curves have nothing to do with grid current.
These curves apply whether grid current flows or not. The x axis is
Vg(max)/Vbias, and across most of the graph that quantity is greater
than 1, ie grid current must be flowing.
>Whenever grid current
>flows in a grid driven amplifier, linearity is compromised.
Rich, you keep saying that in such sweeping, all-inclusive terms.
You may believe it most sincerely, but that still doesn't make it true.
Turn over a few more pages in 'Care & Feeding' to section 4.4.5, on
Grid Driven Amplifiers: "The tetrode or pentode linear amplifier is
usually grid driven in order to take advantage of the high gain of the
tube. A grid driven amplifier can be driven into the grid current region
under proper circumstances."
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
www.ifwtech.demon.co.uk/g3sek
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