The relay control board is fairly simple and can be constructed from perf board. See the 200 Series II relay schematic in the SCHEMATICS section. There is sufficient space inside the 400 or 700 chassis to mount the board and relay near the output terminals.

The original PCB used Malco pins (short solder pins) for interconnections on the top edge. The original relay was a Guardian 900-A410-060713-00 with a coil rated at 120 VAC (725 ohm resistance). Phase Linear designs used a DC coil voltage. This circuit was designed for the 200 power transformer with a 98 VAC main secondary. When using it with a 400 (115 V sec.) or 700 (146 V sec.) it may be necessary to increase the value of R 5 to keep the coil voltage under 50 VDC.

The original Q3 (2N3055) was in a flat plastic package with a metal tab. Any similar substitute part will work OK. A 2N3904 or similar general purpose switching transistor may be substituted for the TIS 97.

RELAY = wires to relay coil, AC = transformer main secondary wires, GND = chassis ground, AMP OUT = single wire from each channel + terminal.

When working correctly, the relay control board will provide a 3 second turn on delay an instantaneous disconnect on power down or when harmful DC is present at the output terminals.

NOTES:

1, The factory did not recommend this modification nor is it necessary in most cases. Although it does guard against DC at the output, it is more for aesthetic reasons on Series II 400's and 700's. A simple in-line fuse will protect against speaker damage caused by DC.
2. This modification is intended for technicians experienced in breadboarding and construction techniques. Inexperienced hobbiests should not attempt it. Do not ask for help if you run into problems. See note 1 above.