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From: liz@poppyrecords.invalid.invalid (Liz Tuddenham)
Newsgroups: sci.electronics.design
Subject: Photocell connection
Date: Sun, 10 Mar 2024 12:30:18 +0000
Organization: Poppy Records
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I've noticed that when gas-filled photocells were used in valve
equipment, they were nearly always supplied with a low-impedance source
of +ve voltage to the anode and the signal was taken off a resistor in
the negative return.  There is a blocking capacitor between the
photocell cathode and the grid of the valve, so the standing current and
DC conditions don't appear to be relevant.

This means the photocell has to be connected by a 2-core screened cable,
which was an expensive luxury in those days.  It also has to be
thoroughly screened to prevent hum, whereas the cathode half-cylinder
would partly screen the anode and reduce the amount of extra screening
needed;  so what was the advantage of taking the signal from the cathode
instead of the anode"?

-- 
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk