I have recently purchased two (supposedly) 872a's off ebay. I wanted to make a set of 4 with my 872AX's, though I found they look different. Unfortunately the AX's are hard to come by. Long story short, it looks like an 872a, but I see no mercury droplets, and when heated there's no mercury fog or coating at the top before it's completely hot. They also have a getter, indicating high vacuum? What have I stumbled across?
True. Unfortunately there is little in the way of markings on the tube. Though judging by the lack of a gap between anode/cathode, the lack of the characteristic bowl shape of mv anodes, and not a speck of mercury in the tubes, I reckon they are indeed 4b32 rectifiers. I hope $20 shipped wasn't a bad price...
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