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4. G. W. Elmen, U. S. Patent, 1,768,237. 



5. C. R. Hanna. Design of Reactances and Transformers Which Carry Direct 



Current. A. I. E. E. Journal, Vol. 46, February 1927, p. 128-31. 



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July 1928, p. 97-109. 



7. H. S. Black. Stabilized Feedback Amplifiers. Elec. Engg. {A. L E. E. Trans.), 



Vol. 53, January 1934, p. 114-20. 



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1924, p. 197-209. 



9. T. Spooner. Audio Frequency Transformer Characteristics. Elec. Journal, 



July 1926, p. 367-75. 



10. F. E. Field. The Evolution of the Input Transformer. Bell Lab. Record, 



Vol. 3, October 1926. 



11. E. L. Schwartz. Permalloy in Audio Transformers. Bell Lab. Record, Vol. 6, 



April 1928. 



12. K. S. Johnson. Transmission Circuits for Telephonic Communication (a book). 



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13. T. E. Shea. Transmission Networks and Wave Filters (a book). D. Van 



Nostrand Company, Inc., 1929. 



14. C. E. Lane. Phase Distortion in Telephone Apparatus. Bell Sys. Tech. Jour., 



V. 9, July 1930, p. 493-521. 



15. Eugene Peterson. Harmonic Production in Ferromagnetic Materials. Bell 



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