No mention of "antique" at all, just "one tube", and when I look at
a 6J6 I see one tube... unless I have had a few too many then?

If someone said "design such-and-such using a single tube", would it be fair
to use a Compactron?

When you describe a circuit as being "single-tube", the implication is that
the tube is not a multi-section device.