The Gallery of Mechanical Amplifiers.

Updated: 12 Oct 2004
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This page is dedicated to amplifiers that are mostly mechanical, rather than those which are electric-in, electric out, such as the carbon-microphone repeaters used in the early days of telephony. These can now be found in the Electromechanical Amplifiers gallery.

THE HIGHAM FRICTIONAL AMPLIFIER FOR GRAMPHONES
In 1901 Daniel Higham (pronounced hi-am) introduced the mechanical friction amplifier; see British patent number 13739. In 1904 he introduced the Higham-A-Phone reproducer, the design using a rosin wheel and friction shoe with a tensile link to the reproducing diaphragm giving effective mechanical amplification. The Columbia company bought up Higham's design in the same year, and used the amplifier technology in their top-of-the-line Twentieth Century Graphophone. This was produced from 1905 to 1908.

Left: The Higham Mechanical amplifier; taken from the diagrams in Patent 13739.

A is the input diaphragm, to which the needle is attached. This modulates the force with which lever D presses shoe L against the rotating friction wheel C. Shoe L moves back and forth in response to the varying friction, against the tension from output diaphragm B.

There was also an invention by G C Marks, apparently applicable to phonographs and telephone repeaters, which refers to Higham's 1901 patent. No further details available at present.

Left: The Columbia Graphophone.

i have to say that no sign of the frictional amplifier is visible here.


THE BROWN FRENOPHONE. 1922

Left: The Brown Frenophone, as displayed in The Science Museum, London.

The Brown Frenophone was an electric-in, mechanical-out amplifier. Since its basic power source was clockwork, I decided it was mostly mechanical and belongs on this page.

This machine looks very much like an antique gramophone playing a very small disk, but it is actually nothing of the kind. The Frenophone was designed to amplify weak radio signals to loudspeaker volume, before it became technically or economically practical to do it with valves.

It did this by using a telephone receiver to modulate the friction between a small shoe and a glass disk rotated by clockwork. The shoe was held by two strings; one end of these terminated in a diaphragm at the throat of a conventional gramophone horn. The shoe was covered with a thin cork layer on its lower surface. The coefficient of friction of cork against glass is high, and this explains the high gain and volume that is reported to have been given by this loudspeaker. Nothing so far has been found about the quality of reproduction.

The handle on the side is for rewinding the clockwork motor.

Left: The official explanation of the method of operation of the Brown Frenophone, as displayed in the glass case.

The only reference I have found to this technology was in the French journal "La Nature" in 1923, where it was described as "haut-parleur amplificateur, le frenophone". Iy is known to have been used by radioamateurs in 1924.

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Below: A close-up of the Frenophone mechanism. Note that the receiver has been swivelled backwards to show the small circular shoe on its two supporting threads. The weight of the receiver was counterbalanced by a cylindrical weight when it was in the lowered (operating) position.

TORQUE AMPLIFIERS
Frictional amplifiers can also be used to magnify torque rather than movement. The classic application was amplifying the very small torques produced by ball-and-disc integrators in mechanical differential analysers and gunnery computers.
See: Vannevar Bush's Differential Analyser. (external link)

You can of course make them out of Meccano: http://users.actcom.co.il/meccano/torqueamplifier.html

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