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  • #16
    I did a little peek around and only found a lower spec 6v6 equivalent in the old Rusky products. My understanding is that a lot of the old model designators are being made on equipment salvaged or bought cheap from many of the western Euro factories. So why change dies and forms and such? Sorry I can't recall my sources as my memory is reaching back to a prior epoch for this So fact check as you like. I'm usually willing to be wrong.

    Of course this doesn't preclude the possibility that the tube inside the 6v6s bottle was once in a completely different Russian bottle with an entirely different base. This doesn't seem like a stretch.

    Looking at old black and white footage from the golden age it's clear that there was a tremendous amount of QC and skilled labor at the factory level that I've read simply doesn't exist today. So the old dies and stamps for, say, el34's of one type or another may be in use, but the tubes don't perform the same due to tolerance and materials. I think some of us have seen a lot of this sort of thing. You know, brand new el34's with regurgitated spec sheets that say the plates can take 800V shorting to the heater at 470V during clipping with all other specs observed.

    From what I gather most of the 6L6 types perform as expected. El34 types are a weak link, as are 6550's and the uber kt types. The kt66 aren't "real" kt66's but still function, as with 6v6 types. The strongest performers for tone AND function seem to be a couple of the 6l6 types, one of the 5881's and a couple of the el84's (just look at what the Carr, Bruno, Fuch's, etc are using). As for el34's, well... We're not going to go on without them, so just use the Ruby selected Shuguang tubes labeled el34b. Try to keep it limited to heads because IMHE they tend to microphony, but otherwise sound and perform well. I use mostly el84's and I'm getting the most joy from the 6n14n/6p14p types with the longevity and or durability suffix codes like EM or K. Most are from the old Reflektor factory. I have about 20 K's right now. They are ruggedized and tested for microphonics. Since my own personal amp is a combo and these tubes are lasting easily three times as long as market versions and sounding great, I am pleased.

    These are my limited observations and experiences on the matter.
    "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

    "If you're not interested in opinions and the experience of others, why even start a thread?
    You can't just expect consent." Helmholtz

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    • #17
      JJ6V6S Curve Traces

      Originally posted by uneumann View Post
      That said - there are lots of these tubes in use and they seem to occupy a nice space between the 6V6 and 6L6. If anyone out there has a curve tracer - a lot of people (especially me) would appreciate it if you could run and post a few pentode curves at varied screen voltages. Even curves from just one tube would be something to work from and reference for comparisons.
      I fired up my uTracer and took the following readings of my JJ6V6S. Raw data also attached. The uTracer is limited to 400V and 200ma.

      Let me know if I can do additional readings to help.

      Solid lines = Ia, dashed =Is

      Vs = 250V
      Click image for larger version

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      Vs = 300V
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      Vs = 350V
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      Vg = 0, varying Vs
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      Transfer Characteristics
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      Tristan
      Attached Files

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      • #18
        Originally posted by tristanc View Post
        I fired up my uTracer and took the following readings of my JJ6V6S. Raw data also attached. The uTracer is limited to 400V and 200ma.

        Tristan
        Excellent! Thanks so much Tristan. They're all great and the Vg=0 curves are really useful to me right now.
        I was looking at the utracer page yesterday and thinking about building one ... what a great project.

        Edit - These curves ARE a good fit to the 6V6GT for the conditions in most spec sheets - except that screen current seems quite a bit higher that the Radiotron values, for example. (I don't think I'm misreading that.)
        My statement above about the JJ curves being different from other 6V6s is wrong - I was comparing two different operating conditions, so of course the curves differed. These curves DO cover my conditions better so they give me better insights into what's going on. The higher screen currents are something I'll consider more carefully.
        Last edited by uneumann; 01-01-2018, 10:06 PM.
        “If you have integrity, nothing else matters. If you don't have integrity, nothing else matters.”
        -Alan K. Simpson, U.S. Senator, Wyoming, 1979-97

        Hofstadter's Law: It always takes longer than you expect, even when you take into account Hofstadter's Law.

        https://sites.google.com/site/stringsandfrets/

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        • #19
          I really like the JJ6V6S as they stand up really well to the high voltages often found in amps that run 6V6 tubes. I have customer that have been running the same set of tubes professionally for three years at 480V. They're my go-to tubes for reliability. NOS tubes are ridiculously priced and for me as a repairman fitting NOS into an amp that's running high voltages is not good economically. I find that most NOS vendors are challenging to say the least when it comes to claiming under their flimsy warranties. Most disappear like cockroaches in a Mediterranean kitchen when the light is switched on.

          The one thing you would never know from a NOS tube is whether it was a return back in the day that's now found its way back into the system, or whether it's a clean-but-used repackaged 'pull'. At least buying a new tube carries some comfort. The JJ6V6 has been out long enough now for the dust to settle on whether its any good or not, and in general the answer is that it is a good tube. The argument whether its a true 6V6 or not doesn't bother me so long as it works as I expect. Some of my customers are super-picky and are fine with the JJ.

          Comment


          • #20
            Originally posted by uneumann View Post
            Excellent! Thanks so much Tristan. They're all great and the Vg=0 curves are really useful to me right now.
            I was looking at the utracer page yesterday and thinking about building one ... what a great project.
            It is great and I'd highly recommend it - for me it was to satisfy my curiosity and help with understanding of the design process. I run it using a bench DC power supply and a few of Pete Millett's breadboard sockets and just re-wire as needed.

            I think it would be worth having an online repository of the dumped data files - a form where people could submit a file with the valve make, year etc etc. Could help with averaging and improved SPICE models. And also could be used to generate curves for particular operating conditions by interpolation and so on.

            Edit - These curves ARE a good fit to the 6V6GT for the conditions in most spec sheets - except that screen current seems quite a bit higher that the Radiotron values, for example. (I don't think I'm misreading that.)
            I checked against the GE 6V6GT data sheet: for ~100V on the anode I make 16mA on the screen at Vg=0, which compares to 18ish mA from the uTracer (are you reading right hand axis?).

            I've a couple of very old 6V6Gs - a Tungsram (England) and a GE (Canada) plus an unidentified one which rattles a lot. I could run the same tests when I have the time.

            T

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            • #21
              Just a thought? Could the JJ6V6S be the same guts as their 7591?

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              • #22
                Originally posted by 1ampman View Post
                Just a thought? Could the JJ6V6S be the same guts as their 7591?
                I've always wondered this myself, but after seeing the uTracer curves, they're not passing anywhere near as much current as the 7591 datasheet shows. Possibly the same plate (and screen?) but with a different cathode, or at least a different heater as the JJ 6V6S heater has a rated draw of 500mA while their 7591 has a rated heater draw of 800mA.

                Comment


                • #23
                  Originally posted by tristanc View Post
                  I fired up my uTracer and took the following readings of my JJ6V6S. Raw data also attached. The uTracer is limited to 400V and 200ma.

                  Let me know if I can do additional readings to help.

                  Solid lines = Ia, dashed =Is

                  Tristan
                  dude, this is AWESOME that you did this. I personally find graphical data, to be a huge design tool. Modern Manufacturers don't seem to publish much in the way of new curves on current production tubes, which I find frustrating sometimes.

                  Richard Kuehnel gives a helpful way of plotting fairly accurate new plate currents (Ip2) based on published plate currents (Ip1) for a given screen voltage, if the desired screen voltage (Vs2) is close to the published value (Vs1).
                  **it's easier for me to show you like this, so I don't screw it up trying to translate it clearly into text**

                  in "Guitar Amplifier Power Amps", he describes it as follows:
                  "In these formulas Vg is the grid voltage for which the plate current is being estimated and Vgc is the grid voltage where the tube goes into cutoff when operated at the published screen voltage"
                  If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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                  • #24
                    Originally posted by tristanc View Post
                    I fired up my uTracer and took the following readings of my JJ6V6S. Raw data also attached. The uTracer is limited to 400V and 200ma.

                    Let me know if I can do additional readings to help.

                    Solid lines = Ia, dashed =Is

                    Vs = 250V

                    Vs = 300V

                    Vs = 350V

                    Vg = 0, varying Vs

                    Transfer Characteristics

                    Tristan
                    Thanks for posting those traces, very interesting. Any additional traces you care to make would be greatly appreciated.
                    I'd like to be able to open your zip file, but I can't seem to be able to open .utd files; could you pack them in another format?
                    Last edited by Bendyha; 01-05-2018, 07:50 PM.

                    Comment


                    • #25
                      Originally posted by Bendyha View Post
                      Thanks for posting those traces, very interesting. Any additional traces you care to make would be greatly appreciated.
                      I'd like to be able to open your zip file, but I can't seem to be able to open .utd files; could you pack them in another format?
                      What values would you like?

                      The .utd files are just text files, so you can rename them to .txt.

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                      • #26
                        years ago i had thought about building that tube tracer, but with the 400V limit I can't take it seriously.
                        "Stand back, I'm holding a calculator." - chinrest

                        "I happen to have an original 1955 Stratocaster! The neck and body have been replaced with top quality Warmoth parts, I upgraded the hardware and put in custom, hand wound pickups. It's fabulous. There's nothing like that vintage tone or owning an original." - Chuck H

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                        • #27
                          Originally posted by bob p View Post
                          years ago i had thought about building that tube tracer, but with the 400V limit I can't take it seriously.
                          That doesnt bother me so much. I just wish it was designed to drive the grids positive.
                          If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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                          • #28
                            I guess it depends on what you want to use it for. If you're just screening preamp tubes it's no big deal, it'd work fine. But if you're trying to create a composite load line diagram for a pair of push pull power tubes, it can't even give you a single set of curves at real world working voltages.
                            "Stand back, I'm holding a calculator." - chinrest

                            "I happen to have an original 1955 Stratocaster! The neck and body have been replaced with top quality Warmoth parts, I upgraded the hardware and put in custom, hand wound pickups. It's fabulous. There's nothing like that vintage tone or owning an original." - Chuck H

                            Comment


                            • #29
                              I get it. 500V would be better, but do you really need anything higher than that?
                              If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

                              Comment


                              • #30
                                I've got lots of amps that run over 500V B+.
                                "Stand back, I'm holding a calculator." - chinrest

                                "I happen to have an original 1955 Stratocaster! The neck and body have been replaced with top quality Warmoth parts, I upgraded the hardware and put in custom, hand wound pickups. It's fabulous. There's nothing like that vintage tone or owning an original." - Chuck H

                                Comment

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