The problem: I couldn't use my Heathkit oscilloscope in a house I lived in during the 1960s because my lab was too far from the power-line input to the house, and the line drop through the house was ...

So you have an old tube-type transmitter as a backup. It ran perfectly when you last turned it on two years ago to substitute for your then-ailing solid-state main transmitter. Now you need it again.