article about a specific Sony radio, the SRF-39FP. It has a transparent plastic body, a simple antenna made of copper wire and ferrite, a AM/FM circuit, amplifier, and tuner and takes one AA battery. 50 yeas ago the AM/FM transistor radio was considered indispensable to every American teenager. This device is the last bastion of that tradition. More here.
The radio is a variant of the SRF-39 which only varies by being opaque. The appendix to that serial number "FP" stands for Federal Prisons. the primary difference being the clear plastic housing that prevents the use of it's chassis to hide contraband. It was one of the first radios to use the CXA1129 30-pin integrated circuit driving stereo headphones. That innovation has kept the design on the shelves for 15 years.
It's primary point of sale is the prison commissary. It's somethign like the Base Exchange on a military base (PX, NEX, MCX or CGX) just with a lot fewer options. In prison s these were established back in 1930 ostensibly to provide prisoners with safe specialty goods not supplied by the prison: playing cards, soaps, sodas, hot sauce, headphones, and radios among other things. They are all stocked by contracted vendors for the Federal Bureau of Prisons or private entities that have inexplicably been entrusted with state corrections. I'll quote that NY times article on the secret sales figures.
"Melissa Dolan, a Sony spokesperson, confirmed in an e-mail that selling portable radios in American prisons has long been a “stable business” that represents “sizable” sales for the company. Of the models available, the SRF-39FP remains an undisputed classic, still found on commissary lists an impressive fifteen years after its initial release, making it nearly as common behind prison walls as Apple’s iPod once was outside of them, despite competition from newer devices like digital radios and MP3 players."The device is actually uncommon outside of prisons. Value among enthusiasts and collectors is on the rise. I just saw one on eBay go for $55. Because of the design of the device it has excellent selectivity, It has a low IF of just 55KHz on the AM band. Numerous posts online by DX'ers instruct the user on how to mod the stock device for improved reception. More here.