MANSBRIDGE CONDENSERS

Radio Record, Volume I, Issue 5, 19 August 1927, Page 14

MANSBRIDGE CONDENSERS

SELF-HEALING PROPERTIES EXPLAINED

At some time or other in reading about wireless apparatus the amateur is bound to have come across the term Mansbridge condenser, and has prob-| ably woudered in what way a Mansbridge condenser differs from any other fixed condenser. If he asks one of his more experienced friends he is probably told it is made of strips of tinfoil and waxed paper, but this is incorrect. A Mansbridge condenser is not so simple as that. Virst of all the name refers to the type, and is named after its inyentor, a post office engineer, and it is not a trade name owned by one particular firm, although there is one firm, which has become associated with the name by its specialising in this form of instrument, The peculiar feature about the Mansbridge condenser is that the insulating medium, or dielectric, and the conducting metal is amalgamated into one strip. We have, therefore, a composite strip, one side an insulator and the | other a conductor.

be separated as might be thought. This is because of the methods used to put the metal on the paper surface. It is done by depositing pure tin in a process somewhat resembling electro-plat-ing upon the paper. In fact, we can be said to have plated one side of the ‘paper with tin. The paper used is a ‘Specially prepared one called cellulose Paper, and rather resembles good guality cigarette paper. , When the tin has been properly deposited the strip is passed between two rollers which are charged at a high potentiai of about 2000 volts. This is be-. cause during the plating process some of the tin is bound to penetrate the pores of the paper and would result in short circuiting any condenser made with that strip. The high voltage, how-' ever, burns away any such faults. A short circuit occurs wherever the. tin penetrates the paper, with the result that the film of metal is burned away, leaving small punctures which can be clearly seen if the strip is held ap to the light. When the short circuiting metal has been burned away the insulating proihe strange thing is that they cannot

perties of the paper are restored, and the composite strip is ready for the next step. Every Mansbridge condenser consists of two of these strips and two strips of pure cellulose paper. The four strips are laid down so that we have a strip of paper, a prepared strip, a paper strip, and another prepared strip. The required length of interleaving strip for any given capacity of condenser is then rolled up, and later pressed flat. It is then impregnated with molten wax at a high pressure and fitted into its case. Contact to the metallic faces of the paper is made by slipping either brass strips between the metallic face and the adjacent paper, or by roiling in short lengths of bare flexible wire during the rolling process. Self-Healing. One of the great advantages of thie Mansbridge condensers is that they seldom break down in use aud are in some respects "self-healing." That means that if a short circuit does occur in them the tin is burnt away at the point of contact and the paper is punctured. This enables the condenser to retain its insulation and so it can be kept indefinitely in service. Lhe small fixed condensers used in other parts of sets differ in that they do consist of definite layers of metal and insulator. In the better qualities the insulator is mica, but some cheap makes use paper instead. These are not Mansbridge condensers, however, because the metal is not an integral part of the insulator as it is in the genuine Mansbridge condenser. A Conclusion. Many experimenters must have wondered if it would not be worth their while to make their own condensers by assembling tinfoil and waxed The Mansbridge condenser factory made as described above is a wonderfully efficient and fcompact article, and no home-made arrangement can compete with it. The cost of tinfoil and waxed paper would amount to several times the cost of a factory-made condenser, the buik would be very great in comparison, and then there is all the trouble. ~