[Amps] Re: [Amps] Driving Impedance

[i4jmy@iol.it]

A tetrode can be grounded grid.

Polarization requirements are not the same than dynamic circuit and 
have nothing to do with the amplifier configuration.
Stated it, and generally speaking, why to bother with a tetrode in a Gg 
and why to be forced in building a second PS.
Use a triode, instad.
All the matter is a bit obscure, it becomes expecially annoying when 
using tubes where screen current has to be zero or anyway very low.

In my experience I never found a tetrode with more gain than a triode 
when used as a Gg amplifier at full power.

73,
Mauri I4JMY





Grids be dynami



> 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, a
ny 
> tetrode will work fine with both grids at RF ground. This is very comm
on 
> 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 lar
ge 
> 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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