I recently acquired a gargeload of about 1000 tubes...most NOS, though only about 10% of which are useful. Even though most of the NOS ones are in boxes, the boxes generally disintegrate just by touching them since they are at least 60 years old!
So I came up with this cheapo idea for a way to hold tubes. With about an 8" length of 1" copper pipe (haven't tested steel conduit but it would probably work the same, would be tougher to sharpen)
With a pipe reamer, I sharpened the inside of one end of the pipe. It cuts utterly perfect sized holes for straightsided octal tubes (5Y3, 6V6, etc;) in styrofoam, and if the inside of the pipe is a tad rough, so much the better. The holes shown were made before I really got the end sharp and left a litle bit of roughness in the styrofoam as shown. Now that I've gotten it nicely sharp. the holes it makes are very clean.

Incidentally, those 6106 tubes = indirectly heated 5Y3 (sort of) shown are quite remarkable. I've never seen tubes take so long to warm up. In a tube tester, after one minute they show no life whatsoever! The filaments take about 2.5 minutes to warm up. Milled ceramic cathodes produce amazingly closely matched diode halves. I'm not sure that matters except to the most fetishy of fetishists, but they FAR outperform brand new 5Y3Ws.