[Amps] Tetrodes in GG Configuration
Will Matney
craxd1 at ezwv.com
Thu Jan 20 02:22:35 EST 2005
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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