Yes Martin. But... That was when the machines were new. Having done some work on the power supply section and having had a good look at the transformer, in my judgment two expansion boards in a MTX would have been pushing the transformer into overloaded territory. It's stated current rating is 1A AC (see here
). That is the AC current rating. Of course, it is possible that the wording on the transformer/PSU is misleading and it actually has a higher current rating. I would have liked to know the VA rating. But then again it is a similar size and weight to what I would expect for that rating of transformer.
The calculated maximum DC current for all
the power supply rails is tricky to work out because the transformer is multi-tapped and three DC supplies are derived from it. So assuming most of the current is for the 5V DC supply, so the transformer is working in centre tapped mode with full wave rectification only, the maximum DC current is 1 x the AC current. But the 12V DC supply works in half wave mode using some of one winding that also supplies the 5V DC line plus another section of winding that is only used for the 12V DC supply. maximum DC current in this case for this mode is 0.28 x the AC current.
So taking the best case, that's a total current of 1A for all
DC supplies. Now the negative supplies can be ignored because they take so little current. But the current on the 5V and the 12V supplies with just one expansion board (32k bytes memory) is significant.
Now, over 30 years later, the transformer will not have changed, but the electrolytic capacitors may have lost capacity, and will be less able to smooth the "rectified DC' and keep the voltage on the regulator inputs within range. So given that CMOS parts are either the only type available new, or are cheaper than or the same / similar price as NMOS or TTL/74LSxxx parts, it is sensible to use CMOS parts.
CMOS parts use much less current compared to NMOS or TTL/74LSxxx parts, so will put less stress on the power supply system components.