[Arran]

Rogers/Deforest Crosley/Majestic liked to use two types during their octal tube era, a 6R7M and a 75M, the electrical specs for a 75M are the same as they are for a type #75, which is what the 6Q7 was based around. The 6R7M is the same as a 6R7/6R7G/6R7GT. Some sets used a 6J5M (spray shielded 6J5/6J5G/6J5GT and an 84M. An 84M, in spite of it's number is a spray shielded 6H6G or 6H6GT, not a rectifier tube. In any event Just Radios has an interchange guide for Rogers types that lists a 6Q7 as a sub for a 75M, also a 6B6M, I'm also sure that I saw a metal 6Q7 used in place of a 75M in at least one set I worked on.
Regards
Arran