Hello. This was found in my Two-Rock CRSv2, it is balanced, measured 7 or 8 on the tube tester. Old Yugoslavian? I don't know NOS stuff, so experts, please chime in! It looks like 2A (T or I, the top is missing of that character) and the line below it is that horseshoe symbol with a dot followed by what looks like 8F There's also a mark inside the tube. Video: Cheers!