[Amps] Determining the Age of A Tube?

[Eric Rosenberg]

I'm using a borrowed ETO 78 (early vintage). The person loaning it to me
(K2PS) has no idea how old the tunes are... he hasn't changed them. Last
weekend (ARRL DX CW) we didn't get more than 1kw out, with lots less than
that on 15 and 10m.

We know the tunes are soft, but how soft are they an dhow do we find out?

Thanks & 73,

Eric W3DQ
Washington, DC