oakstills bain-marie

[The Booze Pipe]

I turned the knob to the right untill the ammeter started reading power, then backed it off until it read near zero, .3 amps or so.

Got it.
You need to find a pot that's slightly larger than 221k so the power is zero when the knob is turned fully to the left.
If I remember correctly 250k +/- 20% is the next higher ohms commonly available.
Due to the nature of a SSVR it will conduct around .3 amps even when there's nothing connected to pins 3 and 4.
It's using this current and voltage drop across pins 1 and 2 for internal power.

So I just soldered on a 250k ohm linear potentiometer. It works better than the original! But I think it could work better still. The power comes on about half way through the cycle, but it is easier to settle on a specific power level, like 11.5 amps. This was just quick testing, nothing in depth.

Would it be possible to use a different resistance to be able to use the full range of the knob?

[shadylane]

100k is the next smaller value that's commonly available, give it a try.
The worst that could happen is the power might not go to zero.