The microwave was launched into a misjudged market.

It was thought necessary for the device to be percieved as able to replace a conventional oven, so it was engineered to handle as large a whole turkey, with the advantage of cooking it faster and with less waste heat into the kitchen.

In physics, cooking always requires more time than heating. The pure heating speed advantage of the microwave was not leveraged until somebody got the idea to make small low-powered units not primarily for cooking but instead for simply heating coffee and snacks in the office. Until that market was saturated, and the price dropped low enough for consumers, and by that time the consumers were already familiar with the device.

Once millions of people could easily put them in their shopping carts, they flew off the shelf.

Source: I was hired as the first computer programmer for an appliance company about the time these were being launched, but I had already been studying businesses for a while.
It required two deliverymen on a truck to carry and install a microwave at this time in the '70's, when the driver alone could usually handle a refigerator. Microwaves were priced comparable to high-end conventional ovens.

OK, I'm old, lets get nostalgic.
It's not the real vintage turkey-sized microwaves like your granny's that I miss having around. Lots of them probably ran for decades after they were made anyway, some might be running still.
What about the low-end bargain units that mainstream consumers buy the most of?
Each decade these achieve lower levels of quality never before thought possible.
Mainstream quality lost forever as the majority of the population becomes too young to remember what it was like.

Fortunately the Alto was not (intentionally and/or largely) engineered to have a finite lifetime. Almost the opposite was the mindset at the time. It was expected to require quite some time to explore the capabilities of such a novel unit, so the electronics were supposed to last for many many years into the future.

That's what makes this restoration quite possibly fully within reach without having to rely on overwhelmingly unrealistic amounts of good fortune.

Also, I do have good ideas about how to handle some of the circuit boards from the Alto pictures I have seen. In my field I kept some '70's-built scientific data systems going continuously since the mid-'80s until retiring them still-working two years ago. These have similar densely populated processing, ROM, and RAM PCB's. All soldering must far exceed NASA specs and be done by a loving operator . . . and that's the tip of the iceberg.

Also remember converting a less-vintage, cheap, but actually-available non-Ball monochrome CRT to replace an original unobtainium old Ball, to interface with a proprietary display system. Just had to figure out where to solder so it would work with a display card it was not intended for.

It can be useful being hands-on to get the best performance out of the electronics itself. A few courses in vacuum tube electronics at an early age seems like it would still be helpful for a lifetime of naural science. Edison was a very clever fellow.

I suppose I would have been more clever not to have discarded a few dozen kilos of Xerox pre-PC office machines two years ago to make room for my working science gear.