This is a cool item that I never quite got around to using in a project. It is a metal frame that holds 7x Alphanumeric Burroughs tubes and sockets.
The tubes are B5971 - they are similar to the much larger 7971's but in a much smaller envelope. As far as I can tell, these are the smallest alphanumeric tubes ever made.
Note - that tested the device and six of the tubes worked fine. The 7th tube may be either bad or just haver very dirty contacts.