Matched tubes

[richard parker]

Is it correct that Aspen Pittman was the guy who introduced us to the idea of matched tubes ?

Many people say the idea is pure snake oil as tubes drift very quickly once you start using them.

Thoughts ?

 

[Dr. Vegetable]

Re: Matched tubes

I don't know how quickly tubes drift, but there are definitely circuit designs that only work properly when matched components are used. Even "identical" solid state transistors can have different properties, for example a push-pull amplifier where two different tubes/transistors are working together, each amplifying only half of the signal. Matching components has been a staple of high-precision circuit construction for a long time, and likely pre-dates Pittman's work. It is expensive to do, because you have to buy a lot of parts and take the time to characterize and sort them, and many rejects will sit unmatched or perhaps be so far out-of-spec as to be unusable in a well balanced circuit. You will absolutely get a cleaner signal out of an amplifier built with properly matched yin-yang components.

I suppose even if the tubes characteristics will drift, you are more likely to have them drift together if they start out matched and are operated together in the same circuit. But that's just a hunch.

I recently ran across this interesting article about tube bias and why Mesa uses matched tubes in their amps, and why they don't provide bias adjustments. It's an interesting read.

 

[beaubrummels]

Re: Matched tubes

There was a point when I went through a couple quartets of power tubes in my Marshall due to the last one by the tranny burning up, and when the other three 'good' ones were measured, none of them matched anymore. Now obviously, the amp had problems, so I don't have good information on whether they began to change prior to the one failure, or if the failure caused all of them to change. But the point is it's possible for a matched set of tubes to change values and diverge from when they were new.

 

[beaubrummels]

Re: Matched tubes

By the way, in a TapeOp interview with Pittman, he mentioned that McIntosh home stereo amplification was already matching tubes and that's where he got the idea.