^^^^Growing up a friend we went to church with was a TV repairman. he had a smaller version of that.
When I got out of electronic school I got a job at a repair shop and that had a suitcase version for what few tube type sets we worked on.
Your story is exactly like mine...same thing,
While in school , I worked part time in a tv repair shop , learned a lot there.
It was easy to convert tube function to transistor and diode, then IC technology.
Jim