The G2DAF configuration was a horrible idea. Don't go there.
G2DAF's original receiver, transmitter and amplifier (as featured for
years in various RSGB publications) used to be in the RSGB Museum... and
guess what? By the end of his life, even G2DAF had modified his own
amplifier to GG!
The problem with connecting both grids of a tetrode to chassis is that
the control grid takes too large a share of the total grid current.
Older tubes of the glass-bottle era were designed for class-C operation
and have robust control grids that can handle the increased dissipation;
but more modern tetrodes do not. They have been optimized for
grid-driven operation in class AB1 which requires much thinner grid
wires which can easily be damaged by overheating.
All tetrodes can be operated correctly in cathode-driven "grounded" grid
by applying separate bias voltages to the two grids. (The manual for the
Tetrode Boards explains this with diagrams:
http://www.ifwtech.co.uk/g3sek/boards/tetrode/tetrode-manual.pdf )
73 from Ian GM3SEK
>-----Original Message-----
>From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Fern
>Rivard
>Sent: 06 December 2016 00:54
>To: amps@contesting.com; Joe
>Subject: Re: [Amps] triode vs tetrode
>
>A better way yet is to go G2DAF where the grid is swapped with either
a
>100
>ohm or 200 ohm non inductive resistor and a pair of 6AX4 are used as
>rectifiers to drive the screens with the resulting dc voltage. To get a
good
>match to your exciter for 50 ohm input, simply put in either a 4:1 or
2:1
>balun.
>I had one of those years ago with a pair of 813's and it worked very
well.
>That screen voltage acted like a clamp circuit and there wasn't any
idle
>current when keyed up but with appropriate drive you had full rf
output.
>73 from Fern Ve7GZ
>
>
>-----Original Message-----
>From: Joe
>Sent: Monday, December 05, 2016 5:06 PM
>To: amps@contesting.com
>Subject: [Amps] triode vs tetrode
>
>OK like a 3-500Z, 3CX bla bla bla etc. are triodes, plate, grid, and
>well filament.
>
>Most of these tubes run grounded grid correct? so the grid is simply
>grounded.
>
>Now the 4CX bla bla bla is plate, screen, grid, and whatever filament
etc.
>
>What would happen if you simply wired it up like triode in grounded
>grid. ground both the screen and the grid, has anyone ever tried that?
>
>Joe WB9SBD
>
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