Scored a ’78 V1 deluxe electric mistress at a garage sale. I am also having this hum issue, only when the effect is on. When the effect is off my signal sounds normal, maybe slightly colored. Like the OP said, the hum is just enough to be unacceptable. All jacks/wires/connections inside look solid. The hum remains. I tried both active & passive pickup equipped guitars. Same hum. Hopefully someone out there will find this thread and help us out. Thanks!