The plastic knob (steel pressing on 76/77 stoves) makes it a spare for a Primus 61 indoor stove. I encountered one when restoring my Primus 77, having a spare fuel tank and components from a ‘61’. ‘77’ control spindle and knob pictured top, ‘61’ components bottom. The plastic knob has a thicker hub section and you can see how its corresponding knob mounting section is longer to accommodate that. Apart from the plastic knob and spindle mount for it, the generator and other components are identical to their 76/77 stove equivalents.
I think that the vaporiser looks thinner on the older 76/77 this is from my Primus 76, stamped U (1930)
