Frequently, you will see vacuum tubes advertised as "matched" or "matched pair". I wonder how many of these sellers really know what "matched" tubes are. A pair of tubes must have more in common than the color of the box they are in or the fact that they are both actually in boxes. They must, also, have more in common than simply similar cathode emission measurements done on a tube tester. True "matched" components (in this case, vacuum tubes) are the result of careful and extensive laboratory testing. Such "matched" units will have similar characterists as measured under various load conditions, grid bias, plate voltage, etc. The good news is that you probably don't need "matched" tubes for your application. If I were retubing a high performance audiophile amplifier, I MIGHT want "matched" tubes. I emphasise "might" because laboratory "matched" tubes are very expensive. Creating "matched" tubes (or any other "matched" component, for that matter) is extremely labor intensive. Usually, many, many like components must be tested to find "matching" units. The bottom line is that most tubes advertised as "matched pairs" are NOT. They are simply tubes of the same type.