| Matched sets usually apply to tube amps that have a all tube output section. So matched sets usually apply to power tubes.
A 12ax7 tube is a preamp tube usually matched is not a concern.
A 12ax7 is actually 2 triodes in one package, so its basically 2 tubes packaged in one glass envelope.
So a matched 12ax7 is somewhat of a marketing gimmick, but you could test each triode separately, and if the gain or Mu of the sections match it can be considered a "matching" 12ax7
Likewise as mentioned it would only serve a purpose in a phase splitter since a ideal phase splitter would have equal gain on both sides.
The long tail pair being the most common phase splitter rarely ever has equal gain because of the topology of the circuit.
So even a "matched" tube wont do much. And alot of phase splitters use higher current 12AT7 or 12AU7 so a matched 12AX7 is pretty much a marketing gimmick.
aside from many opinions on the perfect tube, I really stay away from the Groove Tubes that GC and most music stores stock.
Aside from that a better low noise 12ax7 tube was the 7025
essentially the same mu and gain of a 12ax7 but used a spiral wound heater to reduce hum from the AC powered heaters. And using smaller plates and extra mica spacers to reduce microphonics caused from vibration in portable electronics.
Smaller plate 12ax7's are common with alot of guitar combo amps for this reason but still sold as 12ax7's, and now EH is marketing a spiral wound heater 12ax7. Both of those designs stem from the low noise 7025 that was common with alot of Fender Amps. Chosen for low noise and resistance to vibration.
Last edited by BogeyBass : 01-29-2012 at 03:48 PM.
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