That's about the simplest of broadcasters you could build, just a one transistor oscillator, and a classic circuit in its many forms. I built a few of this type from junked parts, and one used antenna bar and tuner cap from a transistor radio I must have trashed.
I also built on pieces of wood with penny nails, dad had a pickle jar full in the garage. Just wrapping the component wires around the nails didn't give a good connection, so I tried soldering them, but the solder didn't stick the wires to the steel nails, though it melted into the wires underneath the head of the nail, and the connection was fine.
Radio Shack came out with something that's probably a similar circuit, with a tunable loopstick and a fixed capacitor. It was part of their early P-Box kits around 1970. I built the fancy 'AM broadcaster' version that came out later, when I guess Radio Shack realized all kids wanted to be DJs.
It says the P-Box version went 20 feet, and the Broadcaster I got was supposed to go 40 feet, but it barely went outside of the house, just one room coverage. What kind of signal did you get on your build?
Cool about the range Dr. Bob, I would have been happy to get that after being disappointed that my kit's signal was almost nil just outside of my house. I only got more range when I wrapped the transmitter's antenna wire around our rotary phone, and the signal followed the phone line a bit down the street.
Not sure if I tried picking up my AM broadcaster with a crystal receiver at that time, but that probably would have sounded real good!
Those simple AM transmitters have incidental FM going along for the ride, making the bandwidth wider, so it stands to reason that a crystal radio, being wide band could pick up all of the oscillator's signal. I found that highly selective radios sounded bad on oscillator transmitters, muffled.
Antique Radio Forums (ARF) has something on the Greymark that Section 8 is talking about:
That has something I hadn't seen in a P-15 AM band transmitter before, a double-tuned output circuit! Two AM oscillator coils coupled together, through a 10 ohm resistor. That's novel, but those oscillator coils (red screw cans) were probably cheap and that circuit would have lowered harmonics a good bit, and made the signal more stable.
No more 'fatal', than a tube-type table radio with phono input. I would have liked to see the circuit have a separate oscillator driving the final for more stability, lowering FM and antenna tuning effects. That would have required more parts, and a 9 pin tube socket for a dual triode like a 12AU7, and maybe a shielded oscillator coil, but that might have been good for a deluxe model that sold for a few dollars more.