Re: [Amps] Tetrodes in GG Configuration

["Will Matney" <craxd1@ezwv.com>]

On Thu, 20 Jan 2005 07:03:21 +0000, Ian White, G3SEK <G3SEK@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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