There is a lot of great data on these forums and I've been a "lurker" for a couple of years. I recently refinished a Bally Knockout (see before and after pictures below) that was pretty beat up. It required total painting on the outside and playfield as well as other internal repairs - but it's 100% working. It took a lot of time and effort and it was my first Bally (I've refinished a Williams Big Ben from scratch also).
But I have a question for fellow Knockout Owners.
When the double bonus is engaged and the ball lands in the advance bonus 3 hole, does the double bonus stay engaged throughout the ball cycle? On my machine it can easily disengage anytime that it goes through the twirly diamonds (not sure what they are called) or the center alley.