I had a problem with my -32 Bally sound board, after getting it working with changing a couple of parts it was very quiet with no volume adjustment. I swapped over a few other new LM741s (U9), no change.
I read this post about the same problem & it turns out that unless you use a LM741 as per original manufacturer/date code, you need to do a mod.
the mod is outlined here...
https://pinside.com/pinball/forum/topic/volume-problem-after-replacing-u9-on-bally-32-sound-board
The 741s I was using were UA741CN ics, they all didn't work. I got hold of some LM741CM chips, tried them & they all worked fine, volume adjustment was available as normal, so no need to do a mod in the end, these were also a later date code & readily available (08 date code).
So it looks like at least some LM741CNs regardless of date will work & the UA741CNs won't work.