A new 5-channel carrier system for subscriber use employing transistors
B. R. Stachiewicz, R. L. Layburn, D. F. Jamieson · Transactions of the American Institute of Electrical Engineers Part I Communication and Electronics · 1957
THE NEW Subscriber-Carrier System type 561 described in this paper is a result of many months of engineering effort by many individuals in the Stromberg-Carlson organization. The design was undertaken to satisfy a pressing need in the telephone industry for an inexpensive yet good quality system which would help alleviate the critical situation existing in the field of rural service.