Andrews Twin Rectifier Valve |
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This tube is inspired from the Villard
rectifier valve, introduced by the French scientist Paul Villard (1860-1934).
Such valves have two electrodes in a relatively high vacuum, one of which is
a large aluminium spiral, while the other is a
small flat aluminium disc. Owing to the important
asymmetry in the size of the electrodes, resistance to the passage of current
is much less in one direction than in the opposite one, resulting in a
significant suppression of one half wave of an alternating current. As with other cold cathode
tubes, such rectifiers harden with time, and are usually fitted with a
regeneration device which could be of any type. In this valve the
regeneration device is of the condenser type with one of its end connections missing. |
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When large currents were needed
for instantaneous radiography, 2 or 3 valves were used in parallel, joined
across in their mid-part, and sharing the same regeneration device. Hereafter
pictures of triple valves from the Siemens
and Halske catalog of 1911 with installation instructions.
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The present twin valve is 16”
(40cms) long and 16” (40cms) across, and the bulbs are about 5”(12,5cms)
diameter. It bears on one bulb the mark “Andrews Rapid X-Ray Tube, |
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* If not the oldest in the business, the
Grand Old Man among British x-ray manufacturers, Cuthbert Andrews is
certainly the most colorful. He started in the x-ray business in 1910 in a
basement at 35 Hatton Garden ( (E.R.N.Grigg, “The
Trail of the Invisible Light”, Charles C. Thomas, 1965 , p.507) . |
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