These photos are courtesy of Pasquale Rosa. These 911 Envelope Generators differed slightly from the standard. As can be seen in this photo the S-Trigger has been replaced with a V-Trigger and a X1 / X100 switch.

The rear label is non-descriptive.

At the top of the PCB you can see an additional 470 µF capacitor across the 10 µF timing capacitor. 480:10 is 48X, not 100X. At the bottom of the PCB you can see the addition of a transistor and resistor to convert the S-Trig to a V-Trig.

The module uses the revised 91-039 PCB.

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