Three types of Marconi water cooled valves were used at Daventry, five
CAT1s as the R.F. transmitting valves, eight CAM1s as the modulator, and
eight CAR2s used as HT rectifiers for the other valves. All needed a minimum
of 2 gallons of water per minute for cooling. As a point of historical interest,
in 1949 the ‘Old Gentleman’ as it was then known was scrapped and the
building cleared for installation of the new BBC medium wave ‘Third
Programme’ transmitter. Three of the water-cooled valves, one of each of the
types that were used, were kept on display in the entrance hall of the building.
In 1992, when all transmissions finally ceased at Daventry, the 3 valves were
put on display in the main transmitter hall for the closedown day, but they
disappeared. They were subsequently found at the BBC Television Centre in
London as it was being cleared for the move to Salford in 2012. The valves
are currently at the Town Council Museum in Daventry and they are
probably the earliest examples of Marconi water cooled valves to survive.
They are also precious examples of Robert’s contribution to this important
technology.
14
During the mid-to-late 1920s a series of more powerful CAT valves were
developed by the valve group viz., the (oil cooled) CAT2 through to the
CAT9, each driven largely by the growing needs of the world’s broadcasting
companies. By 1930–31 ‘super power’ broadcasting stations began to be
considered and a major advance was made with the CAT10 valve which could
handle an input of 100 kW. By the end of the decade, the M-OV were world
leaders in CAT technology. A large cooled anode transmitting valve (the
CAT12) operated the transatlantic telephone line,
15 and even larger more
powerful valves, the CAT14 and CAT14C (500 kW), were being designed
for use by the BBC, each modulated by Robert’s ‘series-modulation’ method.
These valves were water cooled transmitting triodes (30–40 gallons min
−1 )
with tungsten filaments suitable for use as high frequency amplifiers operating
at up to 10Mc sec
−1
. The CAT14 and CAT14C weighed 71 lb (32.2 kg) and
differed only in that the CAT14C had air cooled valve filament leads whilst
the CAT14 had water cooled leads. These valves were originally built in the
GEC Laboratories—little room being available at Hammersmith—and for
many years during the 1930s and 1940s they were the most powerful
transmitting valves in the world. A mark of their success being that valves of
the CAT14 type were to remain in service in the UK until 1957 (Plate 16.1).
When using CAT valves in a broadcasting station, automatic arrangements
were provided to close down the transmitter should the temperature rise too
much or the coolant flow cease. These arrangements were influenced by the
general atmospheric temperatures, and hot weather could sometimes cause a
station to go ‘off air’. Large valves of the water-cooled variety were also
16 The GEC Laboratories 1930–1939
373
CAT1s as the R.F. transmitting valves, eight CAM1s as the modulator, and
eight CAR2s used as HT rectifiers for the other valves. All needed a minimum
of 2 gallons of water per minute for cooling. As a point of historical interest,
in 1949 the ‘Old Gentleman’ as it was then known was scrapped and the
building cleared for installation of the new BBC medium wave ‘Third
Programme’ transmitter. Three of the water-cooled valves, one of each of the
types that were used, were kept on display in the entrance hall of the building.
In 1992, when all transmissions finally ceased at Daventry, the 3 valves were
put on display in the main transmitter hall for the closedown day, but they
disappeared. They were subsequently found at the BBC Television Centre in
London as it was being cleared for the move to Salford in 2012. The valves
are currently at the Town Council Museum in Daventry and they are
probably the earliest examples of Marconi water cooled valves to survive.
They are also precious examples of Robert’s contribution to this important
technology.
14
During the mid-to-late 1920s a series of more powerful CAT valves were
developed by the valve group viz., the (oil cooled) CAT2 through to the
CAT9, each driven largely by the growing needs of the world’s broadcasting
companies. By 1930–31 ‘super power’ broadcasting stations began to be
considered and a major advance was made with the CAT10 valve which could
handle an input of 100 kW. By the end of the decade, the M-OV were world
leaders in CAT technology. A large cooled anode transmitting valve (the
CAT12) operated the transatlantic telephone line,
15 and even larger more
powerful valves, the CAT14 and CAT14C (500 kW), were being designed
for use by the BBC, each modulated by Robert’s ‘series-modulation’ method.
These valves were water cooled transmitting triodes (30–40 gallons min
−1 )
with tungsten filaments suitable for use as high frequency amplifiers operating
at up to 10Mc sec
−1
. The CAT14 and CAT14C weighed 71 lb (32.2 kg) and
differed only in that the CAT14C had air cooled valve filament leads whilst
the CAT14 had water cooled leads. These valves were originally built in the
GEC Laboratories—little room being available at Hammersmith—and for
many years during the 1930s and 1940s they were the most powerful
transmitting valves in the world. A mark of their success being that valves of
the CAT14 type were to remain in service in the UK until 1957 (Plate 16.1).
When using CAT valves in a broadcasting station, automatic arrangements
were provided to close down the transmitter should the temperature rise too
much or the coolant flow cease. These arrangements were influenced by the
general atmospheric temperatures, and hot weather could sometimes cause a
station to go ‘off air’. Large valves of the water-cooled variety were also
16 The GEC Laboratories 1930–1939
373