[Amps] Tetrodes in GG Configuration

[Bill Fuqua]

Why not put in a 50 or 100 ohm RF cathode resistor(bypassed by RF choke) 
then you would have more negative feedback than grounded grid triode.  You 
may waste 50 or 100 watts in the resistor. But would require Zero watts 
grid drive in AB1. Mind you even though the grounded  grid triode has 
reduced distortion the grid current is still a serious source  of 
nonlinearity.  A biased tetrode such as 4CX250 or 4CX1000 etc would have 
practically no grid current changes during the full RF cycle and RF plate 
current would be the same as the RF cathode current.

I am sure something is wrong with the above. I am brain storming and 
getting a headache.

73
Bill wa4lav


At 02:22 AM 1/20/2005 -0500, Will Matney wrote:
>On Thu, 20 Jan 2005 07:03:21 +0000, Ian White, G3SEK <G3SEK at ifwtech.co.uk>
>wrote:
>
>>k7fm wrote:
>>>
>>>There are some very good reasons to run a tetrode in grounded grid.
>>>Using the 4Cx1000A as an example, running it grid driven will result in
>>>unacceptable distortion products.  To get acceptable levels you must
>>>increase the inverse feedback.  Grounded grid inherently provides
>>>feedback and will improve the distortion products by about 6 db.
>>>Collins ran the 30S-1 with a 4CX-1000A in grounded grid, but also added
>>>negative feedback. The result is an amplifier significantly cleaner
>>>than the tube itself.
>>But don't forget that this amplifier used correct DC grid potentials, ie
>>different for G1 and G2.
>
>Perzactly! When I always mention a G-G circuit as "straight G-G", I mean
>all grids tied to ground. Though they still term them G-G when they have a
>bias and screen voltage applied plus are cathode driven. To me, this type
>should be only called cathode driven and not G-G. G-G should be used only
>for true "grounded grid" circuits only.
>
>
>>
>>Whenever this discussion comes up, there is always uncertainty about
>>exactly what is meant by "grounded".
>>
>>Usually the questioner is meaning to ask: "Can I run a ceramic
>>4CXwhatever with both grids connected direct to chassis, same as you
>>would with a glass 4-something?" Or in other words: "Can I do it the
>>easy way, without screen and grid bias supplies?"
>>
>>The answer to that is No, for the reasons that Rich gave in the very
>>first response.
>>
>
>Perzactly again! Run them the way they were designed to run. Another thing
>I noticed was some forgetting a couple of good old 3-500Z's make for a
>good first amplifier running G-G. That is about one of the easiest amps to
>build bar none.
>
>--
>Using Opera's revolutionary e-mail client: http://www.opera.com/mail/
>
>
>Will
>
>PS: Ian, did you ever work me up anything on those transformer specs? If
>so, e-mail me. Thanks.
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