Taking Charge: The Johnson White House Tapes, 1963-1964, edited and with commentary by Michael R Beschloss, Simon & Schuster, 1997, reviewed by Pastor LaMont Bonath.
"So seized was Johnson by the historical and managerial importance of secretly recording his conversations that on the first night as President, despite all of his other worries, he apparently had the presence of mind to ensure that his first conversations in his new job were captured on a new IBM magnetic belt taping system. Once he moved to the Oval office, Johnson used the Dictaphone system employed by John Kennedy, which recorded conversations on plastic Dictabelts. Johnson thus became the only President to record himself from his first month in office to the last. Between November 1963 and January 1969, LBJ taped about 9,500 conversations, totaling about 643 hours. During the period covered by this volume, LBJ taped about 240 hours of conversation."
I would recommend this book. The footnotes and editor's notes were helpful.