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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