PDP11 have widely been used for controlling industrial machinery. Long before the tiny SPS' were available, this was the smallest computer you could have for this application. And because it was widely used, the supply of spare parts was not difficult. And furthermore, the PDP was a very reliable design that could run 24/7.
We had a customer who run a huge dairy on a redundant PDP11 system. When one processor failed, the other took over immediately. The plant was built by Alfa Laval (a swedish milk machinery maker). When it was replaced a couple of years ago, it was in service for 30 years, 24 hours a day nonstop. ... well except some repair stops

The customer that is still running his PDP has a animal food mill. I don't know exactly what he's doing with the PDP but we just have to replace the disk from time to time. Everything else never had a problem.
The problem with museums is that they already have PDP's. And especially the 11/73 was built in high numbers. On Ebay they are still available and also from hardware brokers.
I have an 11/34 which is running with it's original magnetic core memory. That one I will keep... I'd like to hook up an old disk drive and install a RSTS system
