The list of texts below are just a few of the early EEG Technology Texts. Your research does not need to be limited to these texts.

Binnie CD, Rowan AJ, Gutter TH. A Manual of Electroencephalographic Technology. Cambridge University Press; 1982.
Chapter 1, The Basis of the EEG – pp 1
Chapter 5, Recording Systems – pp 138 – 156

Tyner FS, Knott JR, Mayer WB. Fundamentals of EEG Technology: Basic Concepts and Methods. Raven Press; 1985.
Chapters 1, The EEG, p1
Chapter 2, The EEG Instrument, pp 9-14

Ebersole JS, Pedley TA. Current Practice of Clinical Electroencephalography. Lippincott Williams & Wilkins; 2003.
Chapter 3, Engineering principles, pp 32-70

Gloor P. Hans Berger on the Electroencephalogram of Man. Electroenceph. Clin.Neurophysiol., Suppl. 28; 1969.

Brazier MAB. A History of the Electrical Activity of the Brain, The first Half-Century. Pitman Medical Publishing Co;1961.