[Amps] Re: Fw: 4-400A in Grounded Grid

[k7rdx]

Jim....You should have built a pair of 4-1000`s (Good tubes) and put 6700 or
so on the plate....make those 4-400`s look like chicken feed!
73` Jim.
----- Original Message -----
From: Jan Erik Holm <sm2ekm@telia.com>
To: <amps@contesting.com>
Sent: Saturday, November 09, 2002 9:46 AM
Subject: [Amps] Re: Fw: 4-400A in Grounded Grid


> Could be but the best amp I ever built was with 3 x 4-400A in GG,
> no parasitics no mickey mouse stuff it just runs and runs, could I
> have been lucky perhaps.
> Has around 4 kV on it and pinns the 1 Amp plate meter, puts
> out around 2.5 - 2.7 or so with 200 W drive, sure big difference
> compared to my 4-1000A amp which is nothing but head ache,
> why oh why was I so stupid that I did build sutch an amplifier.
>
> 73 Jim SM2EKM
>
> PS: Remember that I once put 4-250A?s in an SB-220, I just
> shorthed out the zener and it worked quite ok.
> ------------------------------------------------------------------------
>
> skipp isaham wrote:
>
> >Bill,
> >-
> >Some high-u tetrodes by function of tube geometry are
> >not best operated with the grid and screen tied together
> >
> >Grounded grid 4-250A & 4-400A tetrodes should actually
> >be operated with proper division of excitation between the
> >grid and screen which should be the radio of the screen
> >to grid amplification.  This value is about 5  for the 4-400A.
> >
> >Previous Radio Handbooks cover the subject pretty well.
> >Proper ratio of grid/screen excitation may be achieved by
> >tapping the grid at some point on the input circuit.
> >
> >Classic drop in Zero bias operation of the 4-400A  into
> >a 3-400z/3-500z hole is not the best way to go.  In
> >many examples the swap works... it's just not the
> >best option.
> >
> >skipp
> >
> >
> >
> >
>
>
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