The Redmere Soloist
The real reason for having this board on the amp is to cover up all the noises generated by the other effects. It's not exactly a 'Feature'. The gate is switched in by the JAM signals from the Flanger, Sustain and Chorus boards and is a real pain if your playing quietly and forget to turn the Threshold pot right down.
The only change to later boards appears to be the addition of 'S-9-2' and '005 0050' to the track artwork.
BF244B FETs aren't made any more but a Fairchild BF256B (current production ) might do the job. Note that the source and gate pins are reversed on the Fairchild.
Noise Gate Schematic S-9-1 and S-9-2 / 005 0050 Boards
Noise Gate PCB Layout S-9-1 and S-9-2 / 005 0050 Boards
Thanks to Dennis Burns for the photograph on the right of serial number 50046.
(Circuit board marked S-9-1 005 0??)