The Hit Parade 1 Transistor Crystal Radio was made by Bell Products, in St. Louis, MO. in the early 1960s. They were a simple crystal radio, built with a transistor used to amplify the radio stations, a 4 lead capacitor, 2 resistors, a diode, and they still used a crystal radio earplug; with no internal speaker. The Hit Parade radio required two AA size batteries, to play; and it there is an off on switch on the radio.
With the Hit Parade Personal 1 transistor Crystal Radio, you could pick up and listen to more radio stations; than you can with a simple crystal radio, that is not amplified. I received 6 radio stations; but, two of the radio stations played over another radio station. The Hit Parade was also used at ball games; so, you could watch and hear the game on the hit parade transistor crystal radio. Transistor radios grew more and more popular since the 1950s and 1960s; as the transistorized radio circuitry grew. The first transistor speaker radio was the Regency TR1, and was made in 1954. In the middle 1960's transistor radios be more affordable, and were used all over the world.
The Theory of Electronics of a Crystal Radio Set
The World's First Transistor radio - audiouk.com
The Early Radio London Fab Forties ? 1965
The First Transistor - cedmagic.com
Transistor network - Electronic Edition -September 1997
Vintage Transistor Radio - collectorsweekly.com