our phx station had an 8E with one backplane in it and a single diablo hard drive. would be great to buy one of these for the museum . Ed# _www.smecc.org_ (http://www.smecc.org) In a message dated 12/9/2015 7:19:06 A.M. US Mountain Standard Time, radiotest at juno.com writes: At 11:53 PM 12/8/2015, wulfman wrote: They were not. They were either 2 track for mono or 3 track for stereo, and they were physically different from, and not interchangeable with, consumer tape cartridges. Radio carts were introduced in, IIRC, the early 1960s (I would have to check my broadcast equipment catalogs) and predate the Lear 8 track cartridges. Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA http://plymouthcolony.net/starcityeng/index.html