Listen to this Gambling History blog post here
“One of the members of the Journal news staff stopped in at a [Reno, Nevada] casino one night last week, put a nickel in a slot machine and hit the jackpot. The attendant came with $7.50 and gave him another nickel to take the machine off pay.
He did it — you guessed it — three more bars. The attendant set off to fetch another $7.50.
Such a thing happens once in 50,000 tries” (Nevada State Journal, “Around Town” column, Dec. 7, 1952).