transmitter’ or ‘CAT’ valve was conceived, but only after a way of making
reliable joints between glass envelopes and copper anodes was discovered.
76
Even so, this magical ‘art’ was practiced only by the most highly skilled and
highly paid glass blowers, very few of whom were available to the vacuum
industry. There was a clear ‘bottleneck to the progression of cooled anode
technology’. The CAT valves that subsequently appeared were of two types,
77
the ‘demountable’ and the ‘sealed-off’, the difference being that the
demountable valve could be taken down and dis-assembled to replace burned
out filaments or other components, whilst the sealed valve, just like a spent
light bulb, would have to be completely replaced once the filament had
deteriorated. Replacing a filament in a demountable would cost just a few
pennies and could be completed in a few seconds or minutes, but in reality,
the tube was put out of working condition probably for some hours. Time
has to be allowed for the valve to cool before opening and releasing the
vacuum, otherwise oxidation could occur. The process of opening the tube
takes time too—depending on the complexity of the valve—and once the
valve has been re-furbished, the airtight seals and gaskets have to be
re-instated and the valve continuously pumped down to maintain the vacuum. The primary advantage of the demountable was that it could be used at
very high-power levels because burned-out filaments could be easily replaced.
The primary disadvantage comes in a situation when a service via the valve
cannot be interrupted, as in broadcasting. This, coupled with an industry
dislike of the inclusion of a delicate vacuum system
78 which has to be continuously operated, made the sealed-off valve the main contender for continuous high-power broadcasting systems. This was the valve the GEC
concentrated their efforts on, a position fostered by developments in the USA
where sealed-off tubes equally as good as their demountable counterparts were
being produced. Nevertheless, high power demountable valves were made in
the UK, principally by the Metropolitan-Vickers Company of Manchester
and used in the Post Office radio station at Rugby. Demountables were also
used within the GEC Laboratories to study valve cathodes,
79 and the valve
was later to be the first choice in probably the most critical technology of the
second world war (Chap. 17). During the decade, the work of the GEC valve
group overcame the many technical deficiencies of the old glass valves to
create a new generation of sealed-off transmitting valves which became world
leaders during the 1930s. Robert Le Rossignol—along with others—made a
fundamental contribution to the development of large radio transmitting
valves. Indeed, by 1944, (the now Sir) Clifford Patterson said in a lecture
reviewing the laboratories contributions
80 ; ‘from the time he started working
352
D. Sheppard
reliable joints between glass envelopes and copper anodes was discovered.
76
Even so, this magical ‘art’ was practiced only by the most highly skilled and
highly paid glass blowers, very few of whom were available to the vacuum
industry. There was a clear ‘bottleneck to the progression of cooled anode
technology’. The CAT valves that subsequently appeared were of two types,
77
the ‘demountable’ and the ‘sealed-off’, the difference being that the
demountable valve could be taken down and dis-assembled to replace burned
out filaments or other components, whilst the sealed valve, just like a spent
light bulb, would have to be completely replaced once the filament had
deteriorated. Replacing a filament in a demountable would cost just a few
pennies and could be completed in a few seconds or minutes, but in reality,
the tube was put out of working condition probably for some hours. Time
has to be allowed for the valve to cool before opening and releasing the
vacuum, otherwise oxidation could occur. The process of opening the tube
takes time too—depending on the complexity of the valve—and once the
valve has been re-furbished, the airtight seals and gaskets have to be
re-instated and the valve continuously pumped down to maintain the vacuum. The primary advantage of the demountable was that it could be used at
very high-power levels because burned-out filaments could be easily replaced.
The primary disadvantage comes in a situation when a service via the valve
cannot be interrupted, as in broadcasting. This, coupled with an industry
dislike of the inclusion of a delicate vacuum system
78 which has to be continuously operated, made the sealed-off valve the main contender for continuous high-power broadcasting systems. This was the valve the GEC
concentrated their efforts on, a position fostered by developments in the USA
where sealed-off tubes equally as good as their demountable counterparts were
being produced. Nevertheless, high power demountable valves were made in
the UK, principally by the Metropolitan-Vickers Company of Manchester
and used in the Post Office radio station at Rugby. Demountables were also
used within the GEC Laboratories to study valve cathodes,
79 and the valve
was later to be the first choice in probably the most critical technology of the
second world war (Chap. 17). During the decade, the work of the GEC valve
group overcame the many technical deficiencies of the old glass valves to
create a new generation of sealed-off transmitting valves which became world
leaders during the 1930s. Robert Le Rossignol—along with others—made a
fundamental contribution to the development of large radio transmitting
valves. Indeed, by 1944, (the now Sir) Clifford Patterson said in a lecture
reviewing the laboratories contributions
80 ; ‘from the time he started working
352
D. Sheppard