How to match 12AX7 tube pairs. Help please!

Discussion in 'Audio Hardware' started by EddieVanHalen, Aug 12, 2017.

  1. EddieVanHalen

    EddieVanHalen Well-Known Member Thread Starter

    I've recently bought four 12AX7 Hit Ray tubes (Hitachi-Raytheon joint venture,made in Japan) for my Phono preamp which only uses two tubes. On the ebay listing for these tubes it's stated that they are tested. Bellow there's a summary (copy and paste) from their specs as stated by the seller. How would you match these tubes in pairs according to their specs? Tube 1 with tube 4 and tube 2 with tube 3? I know Tube 1 with Tube 2 are a perfect match but then tube 3 with tube 4 would be a less than ideal match. What is your advise at matching these tubes in pairs?
    Thanks in advance.
    4 Vintage Hit-Ray Japanese made 12ax7 vacuum tubes. New in box.

    Tubes have been tested on a Calibrated Hickok TV7 tube tester and test as follows:

    Tube1 : 50/52

    Tube2 : 50/52

    Tube3 : 54/48

    Tube4 :48/46

    Minimum good value on a TV7 tester for a 12ax7 tube is 32. The tube tests within the NOS range!"

  2. JBryan

    JBryan Forum Resident

    Interesting tubes you got there. 12AX7 tubes typically have a long service life and should last even longer in most phono sections so my suggestion would be to put the closest spec'd tubes together. You'll get the best sound quality that way and if they still have plenty of life in them, you'll have +10 years to worry about what to replace them with.

    That said, there's no real way of knowing from the specs as tested how long the tubes will last and you can't really match tubes on a mutual conductance type tester (much less an emission version). The tester does not test at typical operating current/voltages where a tube may show a different spec so a MC tester can only provide an indication of tube performance. There are proper 'matching' testers out there but they are expensive and very few sellers use them. Also, a tube may test in the 'new' range but have lots of hours and could fail immediately or soon after you put to in service. Its a 'roll of the dice' type scenario but for most of us - its all we got so good luck and I hope you enjoy your new tubes for a very long time... :cheers:
    EddieVanHalen likes this.
  3. EddieVanHalen

    EddieVanHalen Well-Known Member Thread Starter

    Thank you JBryan! I'm currently using a pair of Hitachi 12AX7 on my Phono pre and they sound great, nice timber, nice mids, bass with authority but not boomy and very well defined highs but not agressive at all. On my current Hitachi 12AX7 gain is great, they're dead quiet so they have excellent signal to noise ratio and no microphony at all. These are Hitachi branded unlike the ones on the picture which are the actual tubes I got (I haven't received them yet, they're on their way from Canada to Spain) and are Hit Ray branded, a joint venture between Hitachi and Raytheon. I expect these Hit Ray to be as good as my current Hitachi 12AX7, I really love those tubes, they sound outstanding to me.
    Regarding the matching, I think if there are differences on emission between tubes I think there will also be differences in gain and noise between channels, am I right? I've been told as pair of tubes break in and have some use differences between them use to lessen, is this true?
    So you would match tube 1 with tube 2 and tube 3 with tube 4. When I receive them I'll do some experimentation myself, let's see what I can get out of them.
    I paid around 70 Euros for the 4 tubes including shipping, I think it's a good price. Next week I'll be bidding for a matched pair of NOS Matsushita 12AX7, I hope I win the bidding without spending too much as I'm very curious about them.
    Here's a picture of the Hitachi 12AX7 I already have.[​IMG]
    Last edited: Aug 12, 2017
  4. TarnishedEars

    TarnishedEars Forum Resident

    Seattle, WA
    If your preamps employs a typical feedback-based design, then exact matching of the GM between tubes is going to have minimal impact on your sound. But if you have a no feedback design, then matching potentially becomes more important.

    And the GM value has essentially ZERO correlation with how noisy a given tube is going to sound in my experience.
    EddieVanHalen likes this.
  5. EddieVanHalen

    EddieVanHalen Well-Known Member Thread Starter

    Thanks for your reply. My Phono preamp is a Chinese Yaqin MS-23B so it will most likely use feedback.

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