Out visiting a friend in New Mexico this week whose dad picks through old antiques... asked him if he had any tubes kicking around and he brought out a few boxes. Mostly radio tubes but I was amazed to find a single 300B! Tested pretty weak on the tube tester, still pretty cool though to find!
Its always fun when that happens. Several years ago I bought a box of tubes from a guy in Vancouver, WA. I went through it briefly for the usual suspects and stuck it in the closet. A few years later I went through them fairly thoroughly so I could put them out in my garage sale. That's when I noticed the 274B rectifier. It tested pretty strong too.