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Marconiphone single-stage voice amplifier

A one-valve amplifier for use with the early commercial 'Marconiphone' crystal sets or valve receivers. The amplifying valve (a Marconi-Osram DER 'dull emitter') powered by a single dry battery is secured in the base of this set, with its transformer and adjustable rheostat for regulating the voltage of the valve's heating filament. These simple valve amplifiers were also known as 'note magnifiers'. They were more powerful than the non-valve magnetic amplifiers.

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