I am pretty sure the NTE5673/ECG5673 has been used in the past as a suitable drop in Triac sub - good if someone could confirm?
Edit: I tried one & can confirm the NTE5673 will work as a suitable sub for the MAC38-2
Found the Triac sub reference I was referring to here:
Post #668
https://pinside.com/pinball/forum/topic/elektra-owners-club-fans-also-welcome/page/14#post-4615896
Post #672
https://pinside.com/pinball/forum/topic/elektra-owners-club-fans-also-welcome/page/14#post-4617672