Thanks all! As usual you all came through with the answer right away. Armed with your comments above I did a forum search on legacy smoke regulators and now I see that these smoke units are a problem.
It seems to me that the smart thing to do would be to get the smoke regulator replaced on this unit, but while at it have the shop change the 6 ohm resisters to 8 ohm on the entire A-B-A set to prevent future issues. Sound right? Anything else preventive I should do?
I am leaving for a week vacation today but will use the time to find a repair shop forum sponsor and then ship the unit(s) when I return.