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[AMPS] screen voltage supply

To: <amps@contesting.com>
Subject: [AMPS] screen voltage supply
From: G3SEK@ifwtech.demon.co.uk (Ian White, G3SEK)
Date: Fri, 18 Jul 1997 12:50:55 +0100
Lane C. Zeitler wrote:
>Has anyone tried tapping off of the B+ via a dropping resistor to provide
>screen voltage to a tetrode? 
>
>If you only need a 100ma or less wouldn't this work? 
>
Yes, it's a common technique - it can be very power-hungry (work out the
wattage of the dropper resistor) but it does have the advantage that
screen voltage is automatically removed if the B+ fails.

>With acceptable E regulation?
>
Not unless you make it so! A transmitting tetrode is not the same as a
6V6, and if you're using it as a linear amplifier you cannot feed the
screen via a simple dropper resistor. 

You MUST provide shunt voltage stabilization from screen to cathode
(ground), either using passive components (zeners, VR-tubes) or an
active feedback regulator. The regulator MUST be set up to permanently
sink the maximum screen current that the tube can possibly draw on
modulation peaks (plus some) or else the screen voltage will drop out of
regulation on peaks, causing splatter. Personally I favor an active
regulator - for the reasons, see www.ifwtech.demon.co.uk/g3sek/imd1.htm


73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)
                           www.ifwtech.demon.co.uk/g3sek

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