Back in the 1950s and '60s my dad built a few EICO kit devices. They were another supplier of build-it-yourself electronic testing equipment to go along with He

Back in the 1950s and '60s my dad built a few EICO kit devices. They were another supplier of build-it-yourself electronic testing equipment to go along with Heathkit: https://en.wikipedia.org/wiki/Eico https://en.wikipedia.org/wiki/Eico There was a lot of military surplus gear back then too for DIYers.