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  • NOS Tubes & Data

    So, I'm not here to discourage anyone from trying different tubes or to make a new "law" about applications, just wanted to share an experience.

    A few years ago I ordered a couple different "versions" of 12AU7 to put in a Super Twin. I got one plain 12AU7, one 5963, & a 6189 (I believe that's it...). I eventually sent the amp out with the 6189 in place as the 5963 was ringy., as was the AU7. I didn't throw them out cuz I knew sometimes a "bad" tube will work fine in a different application. Of course, I'd paid for them to be tested for noise, but whatever...

    Anyway, I was just goofing around & for the hell of it tried all my preamp tubes in my new build. Sure enough the 5963 started ringing immediately. In the trash with you! Then I looked ip the spec sheet.

    Same pinout, same amplification factor, same everything as a 12AU7. Except: the application. Intended mostly for switching applications that involve long periods of standby. No mention anywhere of audio. There was on the 6189 (I think that's it...) though.

    So I thought, huh. Maybe way back when, before we had all these "reissues" & rebraanding, tube specs DID really mean something! And even though my tube vendor seems to think they're equivalent, maybe sometimes it'll work, but that's just luck... So I'll be checking data sheets BEFORE ordering NOS tubes.

    Anyway, I won't be accepting any more 5963s for audio applications.

    I also tried a NIB Sovtek I'd ordered years ago but never used. Hummed like a whatsit as soon as I plugged it in. Had paid for that one to get tested, too... So lesson learned: plug in ALL your tubes as soon as you order them, so if there's an issue you can get a return!

    Justin
    "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
    "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
    "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

  • #2
    Good info and consideration. I always just took the equivalent part numbers at face value. I don't think I have a lot more NOS/UOS purchases to make, but still docking this in the file for the future.

    As to the hummy Sovtek tube... Yessiree. That's been my experience many times. Sometimes it's hum. Sometimes it's a $h!t ton of emission noise(sounds like deep, swirly wind). Sometimes it's crackles and pfutz's that never stop with burn in. I buy one extra preamp tube for every two that I'll use just so I'm prepared to cull the noisy ones. I'm rarely holding a tube in my hand when it's all over. So that would be a 33% crappy tube rate when paying retail to known vendors!?! And like you I always have my parts on hand long before a build is finished. So I've never returned a tube. I just never think to test them before I'm ready to plug them into the new build. I'm always too exited about soldering another amp together to mess with things like smart prioritization
    "Take two placebos, works twice as well." Enzo

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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    • #3
      When it comes to the 4 digit military tube numbers, you have to look at the tube inside. Most were from computer boards and all they did was switch off and on all day. Some may have double or triple micas, those usually will not be microphonic. I'm gonna guess the later (60's 70's) tubes they often just went back to single mica to save a few cents.

      I've used 6201 for a 12at7 and they are great.

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      • #4
        I didn't pull them from a board. It just seems my tube vendor noted the "identicl" specs & just lumped them all together under "12AU7 NOS (various brands)," & it's still self-oscillatwy even though I paid to have it culled. I've got some 6201s that are fine & a couple 6072s that are awesome. It just seems that the 5963, despite identical parameters, ISN'T really up to snuff for audio. I'll just need to specify "NO 5963s, PLEASE!"

        I've also got a small dumpload od 6DJ8/ECC88 out of an old scope... And a ton of other stuff that's "potentially useful," by which I mean, "RC-coupled amplifier" in the datasheet somewhere. I'll try them out someday.

        Justin
        "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
        "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
        "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

        Comment


        • #5
          Same here on the 6dj8's. Never really found a good schematic using them specifically for guitar. There was a guy "Jbfumo" or something who said he had a circuit using them, think it was cascode type.

          "cascode gain stage can be used as a kind of substitute for a pentode gain stage, and even sounds quite similar to one."

          I don't remember if it was the 5963 or 5965, one of them was closer to a 12AV7 or 12AZ7. I have a pile of 6211, same family, they used to howl something nasty in a V1 spot. I made a Valvecaster preamp (starved plate)(with somewhat higher plate voltage) and the 12au7 and family worked great, abit i didn't try the entire rest of the family in it though, maybe later once i finish 4 or 6 other projects.

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