Peter Chadwick wrote:
>Gas tube regulators.
>
>Someone asked about the dynamic impedance of gas tube regulators. I
>found some RCA info which suggests about 160 ohms - that's for 105 and
>150 volt regulators, both the octals and the miniatures.
'Twas I - thanks for the information, Peter. That's about 480 ohms for a
typical string of two VR105s and a VR150.
>Some years back, there was an amplifier design published in the RSGB
>radio communications magazine using a 4CX1000, where the screen was
>regulated by using 400 1N4148s in series as a shunt regulator. They were
>run at about 40mA forward current, so the dynamic impedance would be
>about 250 ohms, decreasing as the reverse screen current increased the
>current through them. The author also claimed an advantage in the
>negative temp co, so that screen volts decreased as the diodes handled
>more reverse screen current.
So the diode junctions and the 4CX1000 screen grid were both involved in
thermal runaway at about the same speed, but in opposite directions!
>An interesting approach, and the linearity was quite good.
I seem to remember that it was the ONLY passive screen regulator that
would keep that particular 4CX1000 free from runaway, so it was hardly a
strong recommendation.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
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