Does anyone know about the technical aspects of recordings such as Grewal's?

Via email, a reader sends the following question.

From the moment I first saw Grewal in a scrum brandishing a tape player I've wondered about the technical (tradecraft?) aspects of this affair (and what that, in turn, might add to our understanding of Grewal). Do you know (or has it ever been discussed to your knowledge) what exactly Grewal would have used to make the recordings in the first instance?

The question, if it has been raised, has not been fully answered.

Personally, I don't know very much about this. But perhaps someone else does. So can anyone tell us much about such recordings?

Perhaps this picture can help. Anyone recognize the make/model, etc.?