AVO VALVE DATA MANUALS
The Avo VALVE DATA MANUALS are always in a pretty unhygenic condition. I have seen no others than wrecked up books. On the other hand, this is pretty obvious. Just calculate, if the book was used 40 years each day opended 2 time, it was opended 30.000 times.
I don't know how many editions were printed, but I just start collecting the, here. It seems the color stands for the edition number.
It must be said, these manuals are a treasure full of tube data, all tubes with their original operating points. You may just as well use it for any other tube tester, like the AMPLITREX AT1000 which has a very incomplete tube data table by itself.