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.
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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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