Depends on what you're matching...matched pairs, or matched sections. From the Tube FAQ:
3.6 Matched sections vs matched tubes
While purchasing tubes, you may come across the terms ‘matched sections’ and ‘matched pairs’. The meaning and implications of these two terms are covered in detail below.
Matched sections
There can sometimes be more than one active amplification element within a single tube. For example, there are triodes and then there are twin triodes - the 6J5 being an example of the former and the 6SN7 being an example of the latter. In other words, the 6J5 is virtually electrically identical to half a 6SN7.
With multiple sections (triodes, tetrodes, pentodes, etc) within a single tube comes the problem of variation. As a result of material and construction variation, there may be slight mismatches between the two sections of a twin triode like the 6SN7. Or the two sections of a twin beam tetrode like the 6DY7. Or the two sections of a twin pentode like the 6MK8.
Using a suitably equipped GM tester, the 2 sections within a tube can be tested and have their amplification ability measured. As a perfect match between 2 sections is exceedingly rare, a 5% match is the usual ‘gold’ standard with 10% and 15% being lesser grades of matching. This is the meaning of having a tube with ‘matched sections’.
Remember – knowing that a tube has ‘matched sections’ is useless without knowing how close percentage-wise they are matched! One retailer’s ‘matched’ may be 5% while another’s may be 10%!
Matched tubes
Matched tubes take the concept of matching a step further.
With matched tubes, all the sections in all the tubes to be matched must fall within a certain percentage of each other. For example, if we want to have a matched pair of twin triodes, it would mean that we would need to match 4 sections from 2 tubes. If we want a matched quartet of twin triodes, it would mean that we have to match 8 sections from 4 tubes.
Confused? Here’s an example to help you sort things out:
• Imagine we have 3 twin-triode tubes: A, B and C.
• Tube A has GM results 98/95, tube B = 96/97 and tube C = 62/60
• ALL 3 tubes have sections matched to 5%. Hence all 3, when sold individually, can be advertised as having matched sections.
• But ONLY tubes A and B can be sold as a matched pair as all their sections match to within 5%.
As you can see, matching tubes can be a challenge - which is why vendors typically charge you a (sometimes hefty) premium for matched tubes. This premium increases sharply with the number of tubes that need to be matched. Ouch!
But wait - why do we even need matched tubes for amplifier use?
In general, only power tubes need to be matched. Rarely will you come across an amp that requires its preamp tubes be matched. Many amplifiers are designed to require power tubes that have similar cathode currents. Even tubes of the same type made at the same time will have variations in their cathode current, and this is why testing and matching is required.
While few amplifiers actually need matched tubes, it never hurts to have them. Please consult your manufacturer to determine whether your amp needs matched tubes.
