I have heard of these-but until now never seen it.Surprized the VOA studio plant where I used to work didn't have some of these-would have been helpful in our toolkits.The formats used on VOA tapes was full track mono and later full track stereo.This was common in broadcast and other professional uses because of ease of editing and splicing.Worked on LOTS of RR Ampex,Scully,ITC,Nagra,Studer tape machines.Now these are NO LONGER used.All digital from computers.