May 1, 2023 -  Seems like I jinxed myself the other day when I stated that this core memory had worked without errors for four days. I should learn to keep my mouth shut. I started seeing glitches and dropped bits for the last two days. I checked solder joints and such and thought I solved the issues but then they started up again. Just now thought that perhaps I was seeing noise spikes getting through the power supply for the transistor section of the circuit so I have added a choke of about 100mH to the power lead. I also reduced the voltage to the transistor section from 12V to 5V and everything seems to be back in good order. Going to have to cycle the cores many times to see if all is happy once again.

Well, the glitches started up shortly after adding the choke. I took a long close look at all my solder connections and lo and behold I noticed that where two copper foils met, they were barely touching at a tiny speck of one corner and not soldered. That is now soldered and starting another round of testing. I feel good that the glitches have been solved at last.

Four hours later and still working as it should.