Water has a very high thermal capacity so water cooling systems were
relatively compact. In some of the early valves of the CAT type however, oil
instead of water was adopted to retain thermal capacity but avoid the problem
of high frequency losses in the insulation of the water systems. In practice
however, the valve group found that efficient cooling only took place when
incipient boiling occurred at the anode. With ordinary transformer oils, this
temperature was so high as to cause the glass to ‘gas’. However, with oils of
lower boiling point such as ‘kerosene’ (140–160 °C), the vacuum remained
unimpaired. But with all oils, ‘sludging’ had to be guarded against. This
problem was well known to electrical engineers—especially when unsuitable
oils were used in oil cooled transformers. Here a sludge formed on the copper
conductors—especially if oxygen was present—and with CAT valves, this
sludge inhibited dissipation at the anode, raising its temperature and
‘cracking’ the oil just as in a refinery.
Other CAT valves developed by the M-OV during the period—generally
those of about the same wattages as glass valves—were cooled by air, either by
convection or by a forced draught from large air blowers. These were a
development of the metal-envelope valve made under the trade name
‘CATkin’ which in turn was a development of the water-cooled valve. Such
valves offered certain advantages over ordinary glass valves; they could operate
at shorter wavelengths, and because of their much lower operating temperature the anode had an enormous ‘clean-up’ property which was able to
absorb large quantities of gas to maintain the vacuum. And whereas we have
concerned ourselves largely with anode cooling here, it’s important to realise
that the filament leads, which carried a heavy current in the more powerful
valves, also had to be cooled. This was also generally achieved by water or by
air.
16.2.3 CAT Valve Modulation
In addition to his contributions to the construction and cooling of the various
CAT valve(s), Robert also turned his attention to improved methods for
modulating high frequency transmitters via the CAM valve. In this respect he
devised the method of ‘series-modulation’
11 which he subsequently patented
on behalf of GEC in 1933.
12 CAT valves of course were used in the final
stages of amplification of RF signals. These signals consisted of two parts; the
carrier wave (say 1500 m wavelength for a long-wave transmission), upon
which was imposed a modulating signal which varies the properties of the
carrier in accordance with the information to be transmitted, which for radio
16 The GEC Laboratories 1930–1939
371
relatively compact. In some of the early valves of the CAT type however, oil
instead of water was adopted to retain thermal capacity but avoid the problem
of high frequency losses in the insulation of the water systems. In practice
however, the valve group found that efficient cooling only took place when
incipient boiling occurred at the anode. With ordinary transformer oils, this
temperature was so high as to cause the glass to ‘gas’. However, with oils of
lower boiling point such as ‘kerosene’ (140–160 °C), the vacuum remained
unimpaired. But with all oils, ‘sludging’ had to be guarded against. This
problem was well known to electrical engineers—especially when unsuitable
oils were used in oil cooled transformers. Here a sludge formed on the copper
conductors—especially if oxygen was present—and with CAT valves, this
sludge inhibited dissipation at the anode, raising its temperature and
‘cracking’ the oil just as in a refinery.
Other CAT valves developed by the M-OV during the period—generally
those of about the same wattages as glass valves—were cooled by air, either by
convection or by a forced draught from large air blowers. These were a
development of the metal-envelope valve made under the trade name
‘CATkin’ which in turn was a development of the water-cooled valve. Such
valves offered certain advantages over ordinary glass valves; they could operate
at shorter wavelengths, and because of their much lower operating temperature the anode had an enormous ‘clean-up’ property which was able to
absorb large quantities of gas to maintain the vacuum. And whereas we have
concerned ourselves largely with anode cooling here, it’s important to realise
that the filament leads, which carried a heavy current in the more powerful
valves, also had to be cooled. This was also generally achieved by water or by
air.
16.2.3 CAT Valve Modulation
In addition to his contributions to the construction and cooling of the various
CAT valve(s), Robert also turned his attention to improved methods for
modulating high frequency transmitters via the CAM valve. In this respect he
devised the method of ‘series-modulation’
11 which he subsequently patented
on behalf of GEC in 1933.
12 CAT valves of course were used in the final
stages of amplification of RF signals. These signals consisted of two parts; the
carrier wave (say 1500 m wavelength for a long-wave transmission), upon
which was imposed a modulating signal which varies the properties of the
carrier in accordance with the information to be transmitted, which for radio
16 The GEC Laboratories 1930–1939
371