Note
QST, Jun 1962, p. 164.
QST, Jul 1962, p. 154. (description)
QST, Dec 1963, p. 175.
QST, Apr 1964, p. 160.
QST, Mar 1966, p. 144.
TM-1 for cathode keying.
TM-1G for grid block keying.
Disappeared from advertising for 6 months beginning in July 1963, but returned in December as the Model B.
Several improvements include fully adjustable sidetone frequency, greatly reduced current consumption for better battery life, and better impedance matching between the monitor and headphones.