The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 492
Fig. 438.—Connections of National Telephone Co.s Test Set centres where a more sensitive and expensive set could notbe afforded. Fig. 440 shows the inside connections, the lower part beingthe bridge and conductivity arrangement, and the upper partthat used for the insulation test. The latter test… … Fig. 439.— Silvertown Test Set
Telephone
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