transformers (one for power and one for the AC relay) were mounted
inside the metal enclosure. The heat sinks were laid out
horizontally, with speaker and other connections above the heat sink. A cooling fan was used to draw heat away from the heat sinks. Unless the amp was driven hard, the fan usually did not have to run.
List price was $1395.95 and tipped the scales at 70 pounds.
Later designated the D-500 due
to a name dispute with the turntable manufacturer Dual, Phase Linear
discontinued this amp after the 1980 model year when the list price
reached a breath-taking $1600. It was magnificent excess, and
marked the zenith of Phase Linear amplifier design.