22 Different Brands of 12AX7 Tubes Tested Against Each Other

Guest writer Kurt Prange rates 22 12AX7 valves   22-Mar-13


Graph Interpretation

All 12AX7's have an amplification factor (µ) of 100 ("high-mu"). Ideally, every 12AX7 should yield the same gain when placed in the same circuit; however, in reality there are comparative gain differences among 12AX7's.

This graph is based on the average gain and noise measured from different tube brands, using the same number of samples for each brand. It should not be assumed that every single 12AX7 from a specific brand will match its place on this graph. The gain rating is only a relative reference (e.g. a rating of "10" does not mean ten times louder than a "1").




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4 Comments...  Post a comment    original story
Willian    Said...

Discovered your site using Ask. This is a pretty good aitrcle. I hope to see you remove the main point of this aitrcle and make another second aitrcle, maybe include a vid, too?

11-Apr-13 01:48 AM


Willian    Said...

Discovered your site using Ask. This is a pretty good aitrcle. I hope to see you remove the main point of this aitrcle and make another second aitrcle, maybe include a vid, too?

11-Apr-13 01:48 AM


Myles Rose    Said...

I would love to know how they measured "gain" as there is some very misleading information here. Mu can be very high when the actual gain is very low or a tube can have lower conductance or Mu with high gain. One needs to know what the plate resistance of the tubes are and publish or supply that data. This can be a common case of somebody with a tube tester and a bit of knowledge making some incorrect assumptions. I would also love to have more data on his NOS tubes that did not fare well.

The good info is showing how inconsistent things are.

12-Apr-13 05:10 PM


Jim    Said...

Interesting however the Mu voltage is not relative to being any ruler if the tone is horrible ! Metal guys tube roll a few sino ax7 as they grind early and chewing metal is there if you want that ! I want Blues-pop-classic rock with complex thick breakup . Chords have to work also. The Phase inverter is a big deal for me. The sovtek 12ax7Lps keeps it together best yet, Sylvania was good and deferent.

Listen carefully , my smearing sounding highs was in my case from the FX loop tube too dang bright Amperex 12ax7 ! A original Tungsol used did the magic for me. I want tubes that have that tube sound , Sovtek 12ax7wa wb and wc have those round notes. Get your hands on a good Phillips 12ax7 long plate for OD socket its badazz .

Voltage gain measurements are cool and worthy effort with 6 tubes powered at once. What we think we want is not a voltage gain number for me.

Know your amp what tube affects what then common sence testing is inevitable. The v1 is your best sounding usually then the EQ recovery 12ax7 on too your phase inverter. Unplug your effects loop some where and listen too the highs as mine changed the HIGHS way BAD when plugged in. Hope you have fun because it is exploring and adjusting even how you play is affected. Amazing fun !

17-Dec-14 02:36 AM


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