[unruhjonny]

now I'm really slipping...

I thought there was some sort of a spring in the mix, but I cannot picture it in that mix.

Lets call the little metal tag on the back of the knob a 'lock';
The lock is there to prevent the knob from falling off;
The lock has a serrated section which inserts into the back of the knob to hold it in place;
The lock, when viewed on a removed knob will be cocked at an angle - this angle is what places pressure on the volume/tuning shaft, and serves to anchor the lock against the shaft;
As mentioned previously, the lock needs to be pried - in this case you are prying it towards the back of the knob - this un-anchors it, allowing you to pull the knob off the shaft.

The locks can be removed, but I'd discourage it, as they can break, and once broken you will need to source replacements

I hope this helps!

EDIT: maybe the spring goes behind the speaker balance knob?