Looks like more help has arrived. I have a different answer, which I believe to be equally correct, but I will reserve further comment until it is shown to be necessary.

And while I'm uncertain as to the EL-34, I believe that the 6L6GC is the vacuum tube most commonly used in musical instrument amplifiers.

Carbon Tetrachloride's formula is CCl4, meaning that for every one atom of Carbon, there are four additional atoms of Chlorine. My good friend Avogadro tells us that there are 6.02 x 10^23 units per mole in a substance. Since there are five atoms comprising Carbon Tetrachloride, it stands to reason ...

Can we help out? I know where the Carbon Tetrachloride guess went wrong....