The Aiwa AD-6900 (mkI) is a portable cassette player released by the Japanese electronics company Aiwa in the 1980s. It features Dolby B noise reduction technology, operated on four AA batteries, and had an MSRP of around $350 in its day. The AD-6900 is considered a classic and a collector's item due to its sleek design and high-quality sound output, making it a popular choice among vintage audio enthusiasts. The AD-6900 (mkI) was followed by an updated version with microphone and equalizer features known as the AD-6900 (mkII).