Tube Numbers Explained

The model numbers attached to a tube aren't just arbitrary, they actually encode some data about the tube. The first number in a tube's model number corresponds to its filament voltage, the letters in the middle are the actual model of the tube, and the last number is the number of things in the tube.

For example, a 6DJ8 is a type DJ tube, with 8 elements and a 6V heater. This can be really handy when you're looking for a substitute tube, since sometimes a particular tube is kind of expensive, but is available with a different filament voltage for a lot less. For example, 6L6, 12L6, 25L6, 50L6 and 117L6 are the same tube, but with different heater voltages. European tube numbers are different for some reason, for example, the European equivalent to the 6DJ8 is ECC88. No I don't know why they do it like that. 

To complicate things, there's also a third numbering scheme with four digit numbers like 5881 for 6L6, and 6922 for 6DJ8, as well as a fourth, much older system that was used in the 20's and 30's that just consisited of a two-digit number. To cut down on confusion, I will only refer to tubes by their number/letter/number designation on this site.

Section VII: Soldering