Bally Surf-Club (1954) Bingo: Cheating demonstration using a variable transformer

I recently acquired a variable transformer. With a 120 Vac input, I can vary the output between 0 and a bit over 130 Vac.

This reminded me of a story I read somewhere a while ago: Back in the day a variable transformer could be used to cheat on a Bally bingo machine.

The Idea was that the machine first had to be surreptitiously plugged in through the variable transformer.

Then through skill or luck a winning combination had to be achieved.

Then, as the machine started adding up credits the variable transformer’s output voltage would be dropped. Enough so that the machine kept operating but just barely. In that state the replay register would keep adding up credits but the replay counter step up coil would be too weak to accurately step up the wiper. If it was done correctly the machine could rack up credits indefinitely. It it was just close enough, the replay counter would once in a while step up successfully the wiper.

That was all theory… more like a myth or an urban legend.

With my new toy I decided to test that urban legend. For ease of demonstration, I took the glass off and placed the balls by hand for a 5 in line.

Turns out it works: A 100 replay payout went up to 247 replays at around 85 Vac. Off camera when I tested the variac It went well over 300.

As one can notice watching the video, the bingo machine’s energized relays start buzzing loudly and the lamps become dim at around 85 Vac. Not very inconspicuous!

Also Back in the day there were the logistics of bringing a Variac into a bar and getting the payout from the attendant without the variable transformer being noticed. Easier said than done.

The important thing is that it actually works

Note: The blue button on the coin door was added to replace the coin switch.
The door already had a hole in it and the coin switch had become... unreliable. I had some poker machine switches and buttons in the shop