Progress in studies of a millimeter-wave free electron laser amplifier based on a small period planar wiggler and a sheet electron beam is reported. Successful propagation of a 15 A sheet electron beam has been accomplished through a 56-period wiggler magnet (Bw = 5.1 kG, λw = 9.6 mm); this was made possible in part by employing a novel method of edge focusing using offset pole pieces. Status of a 94 GHz pulsed amplifier experiment is discussed. Design parameters are presented for a 150 GHz, 5 MW cw amplifier with peak rf wall heating not, vert, similar1 kW/cm2; such an amplifier may be relevant to plasma heating in future magnetic fusion experimental reactors.