Stepped variable capacitor, made by Marconi's Wireless Telegraph Co. Ltd., London, England in about 1908. Used in radio equipment.
The 'telephone' condenser was used by the radio operator to adjust the sound of the detector to their preference or to match the tone of the transmission being received.
It is called a 'telephone' condenser because it connected in parallel across the headphone terminals (headphones were known as 'telephones' in the early days of radio).
The capacity can be adjusted in steps of 50 units from 0 to 350. The unit is a jar (1/900 µF). The wooden case contains tinfoil sheets with mica insulation, fixed in paraffin wax.
Also known as a stepped variable condenser or stepped variable capacitor.
Wooden box with ebonite top and brass fittings, two terminals and three movable pegs. One peg is broken and is kept in a bag attached to the capacitor.
Donation from Amalgamated Wireless (Australasia) Ltd., 29/12/1924
Metal plate on side of box: MARCONI'S WIRELESS / TELEGRAPH Co Ltd / No 45601 LONDON On top on brass fittings: 50 100 200 Bottom of box: 45601
Type of item
126 mm (Length), 76 mm (Width), 250 mm (Height)
Wikipedia. Accessed 12 December 2012. [Link 1](unit)
[Book] Jensen, Peter. 1994. In Marconi's Footsteps, 1894 - 1920., 1994, 123 Pages
[Book] Hawkhead, J. C. & Dowsett, H. M. 1915. Handbook of Technical Instruction for Wireless Telegraphists. 310., 1915, 186-187 Pages