Dolby B was designed for use with audiocassettes. Dolby A was designed for open reel tapes, and the hardware is available in the market. If you have Dolby B open reel tapes they were probably created to dub cassettes.
Dolby B was also used on Tandberg X-series open-reel recorders. It was useful particularly for Dolby-B encoded FM broadcast with an external equalizer; Radio Shack sold those R-C boxes for a few dollars and I have one or two stashed away with my 4-track cartridge player and other obsolete hardware.
Mike mrichter@xxxxxxx http://www.mrichter.com/