I just picked up a Heathkit Jr. "35" circuit experimenter kit on eBay. I had one of these as a child; I don't remember how it is that we came to own it, but I had an itch to re-read the manual. Buying the manual from vintagemanuals.com would have cost as much as the kit + manual. I remember being befuddled by the descriptions of how transistors worked. It turns out the descriptions of capacitors and transistors were a bit sketchy: I think it is pretty much impossible to understand how the AM radio experiments actually function from the text. The operation of the ferrite-core antenna and the various windings are unexplained as well.
I was a bit surprised to find all four transistors in the kit are identical. Thanks to this Heathkit part cross-reference, I see that they are part 417-118, a.k.a. 2N3393 NPN transistors.