Recommended · for some experience
Tektronix type 555 oscilloscope, over 100 tubes inside!
Why people recommend it
A Mr Carlson's Lab tour of a vintage Tektronix 555 oscilloscope, recommended to anyone learning about older test equipment and how it works inside.
Watch for: Vintage gear, but the general scope knowledge carries over
In their words
Watching some of the restoration videos of old tube/valve devices by Mr. Carlson's Lab, I've heard him describe a circuit element called a "reactor" on several occasions - for instance here, where the circuit includes a "saturable reactor".
vwegert on electronics.stackexchange.com, Oct 2018. CC BY-SA.