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What's the preamp tube that has a metal enclosure on my tube amp?

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  • What's the preamp tube that has a metal enclosure on my tube amp?

    Hey guys, just got done putting in new preamp and power tubes. However, I am confused about what preamp tubes control what. I would imagine it's even more confusing on my Triamp considering I have 9 preamp tubes and 4 power tubes.

    I thought the spacing of the tubes was weird. I have 8 preamp tubes in the front (the rightmost one covered by this metal piece) and one preamp tube in the back along with the 4 power tubes. Is there any rhyme or reason to this?


    Besides that, I did replace every tube except for that metal piece enclosed one (it was a H&K 12AX7 that showed no damaged). I replaced 8 Ruby Tube ECC83S and 4 EH EL34s. The JJs and the Svetlana Winged C EL34s really make the difference Sparkling cleans, no muddiness at all, less hum, tighter overall sound, better gain... finally sounds like the Triamp Mk II I played at Guitar Center (that made me fall in love with the Triamp in the first place). All in all, I think I'll be sticking with these tubes for a while. Unfortunately, there is no trimmer pot on my amp so I have a fixed bias. Need to get that looked at this summer. However, without biasing anything, my matched EL34s sound great
    Originally posted by kevlar3000
    I learned a long time ago that the only thing that mattered regarding tone was what my ears thought.
    Originally posted by Zerberus
    Better is often the enemy of good
    Originally posted by ginormous
    Covers feed the body, originals feed the soul.

  • #2
    hmm... good question, all of my pre-amp tubes have metal casings. I guess maybe on yours they did the first gain stage tube in the casing since its the most critical to excess noise level, and that helps somehow?? i dunno.... the preamp tube in the back could be a phase inverter or something, which might explain why its in a different location.....

    but anyway, thats all just speculation, as you can tell. Glad you like the tubes though!!
    '01 Gibson Les Paul Standard (stock BB V's)
    Squier Fat Strat (stock/duckbucker/stock)
    '66 Fender Bassman
    Fender Champion 600
    Fender Stage 100

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    • #3
      The tube that's closest to your power tubes is your phase inverter. It's important (but not essential depending on whom you ask) to have a balanced triod in that position for optimum performance.
      My Sound Clips

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      • #4
        These are some comments from www.guitaramplifierblueprinting.com on phase inverters.

        Matched phase inverters and output tubes are one of the reasons some amps "sing" and others are pedestrian compared to their brothers and sisters.

        The most overlooked and misunderstood part of the output section is the 12AX7/ECC83 (Marshall style) or 12AT7 (Fender style in vintage cases) Phase Inverter tube. This is the tube that drives the output tubes. A lot of folks that specialize in making amps sound great don't understand this, but fix this accidentally. They tend to use very good tubes, such as JAN spec 5751's etc., where the match is closer, and closer matched tubes in the output section. They also use tubes that sound good in the first gain stage positions, rather than the common Sovtek WA tubes which most manufacturers use (because they are sturdy, not as expensive, and ship well without developing microphonics).
        My Sound Clips

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        • #5
          A good rule of thumb is to replace that phase inverter when you replace the power tubes. They are not expensive, but crucial to your tone. From what I've read, it is very important to get a matched phase inverter. The bottom line with a 12AX7 is that it is actually two small tubes in one glass bottle. If one side is out of whack with the other, your tone is going to suffer.

          When ordering preamp tubes from JJ or GT or anyone else, make sure you specify that you need a matched PI. It'll often run a copule of bux more, but IMHO, it's essential.


          www.CelticAmplifiers.com

          "You can't save everybody, everybody don't wanna be saved."

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          • #6
            Very cool Jeff. Thanks guys about the phase inverter thing. That makes sense that it helps fuel the power/output tubes (it is grouped with them afterall).

            Does this mean if I want better distortion, I should take out my JJ and put in the Groove Tube Mullard copy or some other high gain preamp tube (like the Siemen, Telefunken etc.)?

            I'm still puzzled as to what's so special about the preamp tube in the front row with the metal enclosure... Maybe a JJ will sound great there which will free up a space for a better preamp in the phase inverter.

            The sound is excellent, and I mean excellent so far. If it can get even better, I say "bring it on"!

            Man, my lead tone is killer (definitely nods to Vai's "Die To Live" (very rich) as is the Marshall channels, but I still get Fender like chime.... so very sweet (almost makes me forget about those other high end amps... like Gearjoneser tempting me with his Bogner )
            Originally posted by kevlar3000
            I learned a long time ago that the only thing that mattered regarding tone was what my ears thought.
            Originally posted by Zerberus
            Better is often the enemy of good
            Originally posted by ginormous
            Covers feed the body, originals feed the soul.

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            • #7
              The metal covers are shields for noise. Did you buy your amp used? If so, the other ones probably had covers as well for noise. Someone might have taken them off and not bothered to include them when you bought your amp.

              If you bought it new, then it's probably the one on the end (V1) which is usually the most critical preamp tube.

              I'm not sure that the JJ preamp tube is any more or less high gain than some of the others out there. If it's a 12AX7, then you've got alledgely the same amount of gain no matter the brand. Theoretically.

              Some folks will place a higher gain tube like an 12AX7 in a slot that takes soemthing like a 12AT7 or vice vesus. That's usually okay for a preamp, but you don't want to do that with your PI. If it calls for a 12AX7, use a 12AX7 in the phase inverter.

              In the case of "better distortion", better tubes in the amp will give you better distortion.


              www.CelticAmplifiers.com

              "You can't save everybody, everybody don't wanna be saved."

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              • #8
                Thanks a lot Scott! I did buy the amp used, but you're probably very correct about the V1 preamp tube (it is placed at the end).

                Yes, it is strange, but the phase inverter comes with 12ax7s. Guess I should go on Fleabay and get a NOS to put in there After all, even better distortion wouldn't hurt

                Thanks again guys. Scott you just made sense of this whole thing for me
                Originally posted by kevlar3000
                I learned a long time ago that the only thing that mattered regarding tone was what my ears thought.
                Originally posted by Zerberus
                Better is often the enemy of good
                Originally posted by ginormous
                Covers feed the body, originals feed the soul.

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                • #9
                  NOOOOOOOOOOOOOO!

                  Do not go ebay for NOS tubes. You'll likely get a POS not a NOS (piece of sh+t)

                  Go to KCANOStubes.com or that guy that joe recommended.


                  www.CelticAmplifiers.com

                  "You can't save everybody, everybody don't wanna be saved."

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                  • #10
                    Lol... ok ok... kcanostubes it is

                    Thanks for saving me
                    Originally posted by kevlar3000
                    I learned a long time ago that the only thing that mattered regarding tone was what my ears thought.
                    Originally posted by Zerberus
                    Better is often the enemy of good
                    Originally posted by ginormous
                    Covers feed the body, originals feed the soul.

                    Comment


                    • #11
                      That's cool that you got that amp up to full potential now.
                      That fixed bias is fine because the new power tubes are pretty similar to the originals, just a little better. It's probably right in the right range and the Svets run strong, so it's fine.

                      I wouldn't worry too much about that phase inverter tube.
                      Just leave the one that's there, or swap it with your 3 or 4 pre tube, or something. You're pretty much done.

                      Do you use the amp's boosts or have them on all the time?

                      Some guys on these types of heads just leave the boost on all the time, then turn the amp down a little, or the opposite.
                      Originally posted by Boogie Bill
                      I've got 60 guitars...but 49 trumpets is just...INSANITY! WTF!

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                      • #12
                        Re: What's the preamp tube that has a metal enclosure on my tube amp?

                        a balanced phase inverter will help improve output, and can REDUCE distortion. the imbalance caused between an umatched PI tube, actually can contribute to the overall tone and flavor of an amp.

                        germ
                        Jeremy Ledford
                        Tone Guru Extroardinaire
                        Tone Shop

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                        • #13
                          Re: What's the preamp tube that has a metal enclosure on my tube amp?

                          Originally posted by lastwinj
                          a balanced phase inverter will help improve output, and can REDUCE distortion. the imbalance caused between an umatched PI tube, actually can contribute to the overall tone and flavor of an amp.

                          germ
                          hey, germ ...
                          I've read through the stuff on Myles' site regarding a matched PI, and I think he's also said that some circuits benefit more than others.
                          I think the matched PI may improve the feel of the amp, and help the tranny run a little cooler ..

                          does that sound correct?
                          "music heals"
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