Announcement

Collapse
No announcement yet.

Modern EL34 reliability?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Last time I ordered the 4xJJ EL34 and one of them failed after a year or so. Currently in the same amp I have 4xJJ EL34 II tubes which are different "īmproved" version of their regular EL34s which bias properly at more negative voltages. We'll see how long they'll last.

    Comment


    • Looking at the date of my last post it turns out that those JJ EL34 II lasted less than a year after a very moderate use. One of them became very microphonic and developed erratic behavior currentwise (going up to +100mA). "Knocking" tests on the chassis and on the tubes caused sparks inside the tube which brought my tests to an end.
      Plate voltage was 475V. I used zeners to lower the screen voltage down to 445V. The tubes were moderately fan cooled. Other than that tubes' sound was good.
      In the same time two of the tube from the JJ EL34 set are still working in another amp and I'm retubing an amp that had two of the same type installed and that was used every week for couple of hours for two years which looks like a hit and miss situation.
      Now I'm wondering whether to try a JJ 6CA7 or to go for Chinese EL34B. I see also some EL34BW for sale but can't find any opinions on those.
      Last edited by Gregg; 06-23-2019, 09:11 PM.

      Comment


      • Originally posted by Gregg View Post
        Looking at the date of my last post it turns out that those JJ EL34 II lasted less than a year after a very moderate use. One of them became very microphonic and developed erratic behavior currentwise (going up to +100mA). "Knocking" tests on the chassis and on the tubes caused sparks inside the tube which brought my tests to an end.
        Plate voltage was 475V. I used zeners to lower the screen voltage down to 445V. The tubes were moderately fan cooled. Other than that tubes' sound was good.
        In the same time two of the tube from the JJ EL34 set are still working in another amp and I'm retubing an amp that had two of the same type installed and that was used every week for couple of hours for two years which looks like a hit and miss situation.
        Now I'm wondering whether to try a JJ 6CA7 or to go for Chinese EL34B. I see also some EL34BW for sale but can't find any opinions on those.
        Go Chinese (if your government hasn’t banned Chinese imports yet &#128577. They seem to be robust.

        Treat them as 20W tubes (= bias them cooler).

        Be wary of customers who run their amps through power attenuators.

        No point in replacing pairs in a quad of EL34s IMO. You want the whole quad to be matched, especially at those voltages. Otherwise the current will pick the path of least resistance when the amp is cranked (which will be the pair that runs hotter)

        YMMV
        Building a better world (one tube amp at a time)

        "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

        Comment


        • I running for month Tung Sol el34b with 490v into screen grids and common 220k grid leak for a pair , biased pretty high (75 percent around) into 1.9k OT .No sign it will given up.
          "If it measures good and sounds bad, it is bad. If it measures bad and sounds good, you are measuring the wrong things."

          Comment


          • I've always had problems with JJ's of all type.

            I have used a Hotplate with my own Marshalls with EH EL34's with no failures.

            Comment


            • Hate to bring more bad news, but according to Shuguang, their EL34B tubes are tetrodes, not pentodes.
              Their EL34A was a pentode, but was discontinued, likely because of problems with reliability.

              Comment


              • Originally posted by Diablo View Post
                Hate to bring more bad news, but according to Shuguang, their EL34B tubes are tetrodes, not pentodes.
                Their EL34A was a pentode, but was discontinued, likely because of problems with reliability.
                so more like a 6CA7 or a KT77 then?
                Building a better world (one tube amp at a time)

                "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

                Comment


                • Originally posted by tubeswell View Post
                  so more like a 6CA7 or a KT77 then?
                  Yes, some folks claim that the EL34B and KT77 have the same internal parts. I don’t know if that’s true or not.
                  I do know that The Shuguang EL34B tubes sound a lot different (and better) than NOS 6L6GC tubes in my Tweed Twin 5E8A clone. Less emphasis on high frequency and more on midrange. I originally thought it was because it was a pentode, whoops wrong.

                  Comment


                  • It should be possible to tell a pentode from a beam tetrode by dissecting a (defective) tube and see if it has beam confining/reflecting plates or a third (suppressor) grid.
                    - Own Opinions Only -

                    Comment


                    • Originally posted by Helmholtz View Post
                      It should be possible to tell a pentode from a beam tetrode by dissecting a (defective) tube and see if it has beam confining/reflecting plates or a third (suppressor) grid.
                      I have a couple of pairs of this tube. I had to buy three pairs to get one that wasn't too microphonic to use in a combo amp project So these ones are a bit too microphonic for combo amp use but I'm saving them in case I can ever use them in a head amp. A local customer has the least microphonic pair, but he doesn't use the amp much. Not sure what my point is except that I have this tube on hand and if one ever dies I'll open it up for look.
                      "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

                      Comment


                      • I have counted three grids...

                        Click image for larger version

Name:	el34b.jpg
Views:	1
Size:	218.1 KB
ID:	856306

                        Comment


                        • Originally posted by Pedro Vecino View Post
                          I have counted three grids...

                          [ATTACH=CONFIG]56345[/ATTACH]
                          So pentode.
                          - Own Opinions Only -

                          Comment


                          • So why does Shuguang think it's a tetrode
                            "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

                            Comment


                            • Originally posted by Chuck H View Post
                              So why does Shuguang think it's a tetrode
                              Good question, provided we are speaking of the same tube.

                              The whole story seems obscure to me. I mean, why should a manufacturer give his tetrode the name of a classic pentode? Tetrodes and pentodes can't have exact same charts: different curvatures and screen currents.

                              If the EL34B actually was a tetrode and behaves like a KT77, why not call it a KT77?
                              (IMO, the KT77 is the more advanced design.)
                              - Own Opinions Only -

                              Comment


                              • Or someone made an error.

                                According to the Shuguang web site the EL34B is a pentode. They make that and the EL156. Their listing of beam tetrodes does not contain any EL34 types.

                                http://shuguangtube.com/e_products/?big_id=1&small_id=7
                                Education is what you're left with after you have forgotten what you have learned.

                                Comment

                                Working...
                                X