Richard wrote:
>
>
>>Greetings,
>>
>>What's the input impedance for a GG 4CX800A?
>>
>With a 2w? grid, running it in g-g might not be a wonderful idea. The
>4cx800 is designed for Class AB1, which means 0 grid current.
>
With the correct DC voltages applied to the control grid and screen, any
tetrode will work fine with both grids at RF ground. This is very common
at VHF and above, and occasionally seen at HF.
According to the way the power supply is wired, you can chassis-ground
either grid, and RF-bypass the other one; or you can DC-ground the
cathode and RF-bypass both grids.
As Rich says, what you can *not* do is run a modern tetrode with both
grids directly grounded to the chassis. The control grid takes too large
a share of the combined grid current.
Unfortunately - and wrongly - this method of operation seems to be what
most hams understand as "Grounded Grid". It only works with the old
glass tubes because they were primarily designed for Class C, and have
very hefty control grids that can stand the extra current. But even
these tetrodes were never designed to be operated with both grids
chassis-grounded - it's a ham invention.
--
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
New e-mail: g3sek@ifwtech.co.uk
New website: http://www.ifwtech.co.uk/g3sek
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