I just found un-fired Optimus 77a. It was complete with user manual. There was card board box also, but it was not complete (lid was missing and it was taped to keep it together). User manual tells that it burns 40 min with one burner fill. Box tells that both kettles are 1,33 liter and weight is 0,7 kg. (I weight it and result was 740 gr). Interesting to note that burner's inner wall has two notches that fuel can flow to space between inner and outer wall through them. That's a different construction compared to Trangia's burner. I would guess that is't from end of 70's (or early 80's) since box has price tag 89 mk (Finnish marks). I bought my first Trangia on early 80's and it's price was just below 100 mk.