Tube matching simplified

As I was going through some boxes in the closet today I found a couple of old power tubes. One was on it’s way out so obviously I pulled both and replaced them with a new matched pair. My son happened to be in there with me and asked me what they were. I tried to explain but he though they just looked like some cool Star Wars thermal detonators or something. I told him I was throwing them out because one of them was no good. That left him with an even more shocked look on his face.

To try to explain to a 7 year old why one power tube is no good by itself is a difficult task. If one of them technically works why do you have to throw it out?  I tried to explain that the pair needed to work together and that if one could not then the other would be no good.  I tried to explain that tubes all have their own special characteristics and that you need to use two that are just the same to make an amplifier work properly. 

At this point I though I was done, but he asked one more question.  Why do the two have to be the same and why are they all different.  The first part just came to me, “Its like getting on the see saw”. If  a 7 year old and a12 year old get on the see saw together they will be way out of sync.  One will push or pull more than the other. The second part was left as, “Tubes are like people, we are all basically the same in that we are all humans, but each person has their own traits”  I think he bought it. 

While this is very over simplified I think it works. I am still mystified by this sometimes too but I understand the importance of matching your power tubes to get the most out of your amp.

Here are a few more technical articles on tube matching.
http://www.tubeaudiostore.com/virofpowtubm.html
http://www.tubeaudiostore.com/tubmatdem.html