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The parent company was the Cleartron Vacuum Tube Company of the USA. The UK subsidiary made valves in the years 1925 to 1927 in a factory at 21 Cumberland St Birmingham, the offices were located at 1 Charing Cross Rd, London SW1. It is believed that some assembly was conducted in the UK but generally the valves were of American design and many were believed to have been imported.
The four valve types introduced in 1925 were:
CT08. A low consumption dull emitter triode with a filament ration of 0.08 Amps at 3 Volts. Mounted on a B4 base it was designed for general purpose amplification.
CT15. This valve had the same operating characteristics as the CT08 but was fitted with a filament whose rating was 1.8 Volts and 0.15 Amps.
CT25. This was an audio output valve designed to be of low impedance to produce power. The filament was rated at 5 Volts at 0.25 Amps.
CT25B. This valve was a high amplification factor, general purpose type that also had a 5 Volt 0.25 Amp filament.
The three valves released in 1926 were styled 'Plus' valves and were all sold for AF amplification.
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