Radio Valves

Radions Repaired Cossor 'R' type

Bright emitter, phosphorus getter, 'R' type triode

R Type
Repaired 'R' type

The bright orange colour of this valve is caused by the use of red phosphorus as a getter. One of the problems in achieving a high vacuum in valves was the presence of water vapor adhering to the glass. The vacuum pumps in use before about 1918 were incapable of or uneconomic to use to obtain the required vacuum. Even when the tube was baked at high temperature the pumping time could exceed an hour. On Apr 16, 1895 Arturo Malignani had patented a method of absorbing almost all the remaining gases in a bulb by heating it with red phosphorus present (U.S. patent 537,693). Apart from trapping any water vapour, one of the key reactions is the formation of phosphorus pentanitride, thus scavenging the residual nitrogen as well. Pumping times could be reduced to a few minutes by this means.

This method of gettering was used for many 'R' type and related valves, before pumps improved. Phosphorus getters are still used in incandescent lamps but use in valves had been abandoned by major makers before the end of the First World War.

The construction is typical of a vertical 'R' type with a cylindrical anode, spiral grid and a simple linear tungsten filament which dissipated about 4 watts (4V 1A). These valves had typical gains of 6 to 8 and operated with 30-80V on the anode. Power dissipation had to be low as phosphorus gettering is ineffective if the bulb temperature reaches 200C.

The engraving.

This valve bears the engraving :-

"17 10"

(see image of part). Valves were very expensive and in very short supply for a large demand in the later years of the First World War and repair of valves was used as a way of increasing production. I cannot find any evidence of this repair being carried out as a commericial activity after hostilities ceased. It seems relatively unlikely as there were considerable quantities of military surplus valves available to a relatively small market.

Base marking
The base marking.

The "17 10" could possibly be a date code for October 1917 and this valve could be one of those surplus valves. If so it must have originally been manufactured, used, worn out and returned for repair before that. The only clue to the original maker is the trade mark of "C.V.C. Ltd." impressed in the base insulating disk. This is the trademark of A.C. Cossor Ltd., so this valve is probably a Cossor 'R' type. It does not have the classic Cossor cap shaped anode, introduced in 1922.

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This page last modified by AJC on Friday 26th Mar 2010