Exactly, but a lot of older measurement equipment is repairable. I cant imagine a person with very little electronics engineering knowledge repairing current electronics. SMT components everywhere and no tools available at a hobby shop to service them (hot air soldering station, precision tweezers). Having schematics at the inside would like in the old television sets would be a great help (plus board layouts), but this is never going to happen.
But most of the modern equipment that fails, it is usually the power supply that breaks. Either bad capacitors with too high ESR or fried switching transistors.
You use a 547? How do you deal with the HV transformer rot that happens to a lot of post 1960 500 series oscilloscope? I have the single timebase variant of the 547, the 544 that I use for measurements that are too dangerous for my digital or analog scope, but I cant use it longer then two hours before the HV stops working and the screen goes.
Surplus russian tunnel diodes? Where do you get these?