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A triode pentode is a thermionic valve, also known as a vacuum tube (USA). It comprises a triode which has three electrodes and a pentode which has five electrodes, both sections of the valve are enclosed in a single glass envelope.
They were often used in domestic audio amplifiers in the 'valve era' where the triode section acted as a preamplifier to increase the amplitude of the low level signal from the input source such as a tape head or a crystal pick-up; and the pentode section provided sufficient power amplification to drive a small loudspeaker.
Minimising the number of valves in such designs significantly reduced the overall power consumption, heat dissipation and manufacturing cost of the equipment. It also reduced the retail price, making record players more affordable to the domestic consumer.
Triode pentodes are still used in some current production, British built Hi Fi amplifiers because, with careful attention to the design, they can be configured to out-perform double triodes (two triodes in a single envelope) in the driver stages.
Submitted by Graham Stannett (Croxley Audio). I would be grateful if you would be kind enough to contact me if you wish to amend this WikiAnswer or if you would like more information regarding valve amplifiers.
