Quoted from baldtwit:I usually go the opposite of careful. With the power to the socket off, remove the lamp and with a small flat-bladed screwdriver pry the center tab from the front pretty much all the way towards you/up ...so the tip is nearly touching the side of the socket. It'll spring back most of the way. If it breaks, the tension was crap anyway.
if the lamp has a deep divot in the tip, swirl the tip hard on a flat metal surface ... like an anvil on a bench vise. The tip is soft and can be reshaped to remove the divot.
This thread is useful to me since one of my current projects is a 57 Bally Circus - http://www.ipdb.org/machine.cgi?id=520 - which is from an era when Bally was mostly making Bingos, and the OPs sockets are exactly the kind that Circus has...a huge amount of them I might add. My initial thought was to replace them all with more modern ones as someone suggested, but there's just way too many.
So I appreciate baldtwit's approach and suggestions - I'll post any tips/experience/useful info I might encounter while going through the back-box of this title.