These photos are courtesy of Tom Szakaly ( ELP tribute 'Noddy's Puncture).  This is a very rare headphone monitor which can be seen in this photo with Bob Moog at Jazz in the Garden.

This module is unique in that it has its own AC power supply. The headphone amplifier uses a pair of GE PA237 2 watt amplifier ICs.

PA237 Data Sheet

The panel has a number of features. At the top is a switch to monitor external trunk signals connected at the rear of the module. An A440 reference signal was also brought in through the rear panel and could be monitored by pulling out the bottom control. The top control says to pull out for a 30% mix which might have been a way to monitor at a fixed reference level.

The rear connector label shows the external connections.

This right side view shows the power transformer and AC power cord along with the PA237 ICs.

The left side shows some of the PCB wiring. The rectifiers for the power supply can be seen on the bracket facing the panel.

This image shows the minimal number of components required for the amplifier.

The rear of the PCB has minimal wiring.

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