When I was a kid, you could buy "electronics lab" type toys with a handful of components connected to little metal springs that you could tuck wires into to build various circuits. There was also Lectron, which had the components in clear plastic blocks with magnetic connectors and the schematic symbol printed on top, so you'd just arrange the blocks into the schematic, and it would actually be the circuit! One day, I scrounged an older such toy from the trash. It had a vacuum tube socket! I didn't have the instruction book, but knew enough to build various things with it. Unfortunately, it got thrown away, and such things haven't been made in decades. Or so I thought. It turns out electronic building sets are alive and well. You can get this small set with book for the princely sum of six dollars. For something more like the old Lectron, Gakken has resumed production of
their EX-150 electronics kit (AKA Denshi Blocks),
But a friend sent me this link to a zero voltage oscillator (in German), and I noticed the electronics kit in the background. A little asking around revealed this:
Description here, vendor site here. For €99, you can buy a modern production prototyping system with the usual proto-board, 4 tube sockets, 2 potentiometers, and a variable capacitor. Slick! However, they only ship to Germany and Switzerland unless arrangements are made in advance. I've emailed them to see if they'll sell one to me in the US. I hope my machine translation "Ich möchte Ihr Modell RT-100 kaufen und über PayPal im Voraus zahlen, aber ich wohne in den Vereinigten Staaten." made some sort of sense.