I have come to the conclusion that 74LS74 performs slightly better than the 7474 in the ACI output flip flop application. This is because of a slightly higher output voltage level in the LS series part. As noted in the past, the 7474 is slightly less subject to the potential floating input problem than the 74LS74. However, I have been exclusively using a 74LS74 on my own ACI without difficulty for a long time, so I think the floating input issue is more of a theoretical issue than an actual problem. However, I would verify any tapes you make before declaring your program or data is backed up.

Because of this change in thinking, I will no longer be providing the alternate 7474 ICs with my ACI kits.