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  • Hammond/Leslie tube question



    What (if any) tubes should be replaced before they fail? Are there any tubes which can harm an amp or speakers when they fail?</p>

    </p>

    Specifically in the 147/122 leslie and also in the amps of consoles and spinets (AO-28 except for the L100?)</p>

    </p>

    Not totally unrelated, but I noticed that the OC3 bulb in my 147 was flickering for a few moments after startup. What exactly does the OC3 do? It is drawn as a light bulb on the schematic. When does it go bad?</p>

    </p>

    </p>

  • #2
    Re: Hammond/Leslie tube question




    The only tubes that can cause damage are the 6550's in the Leslie. Actually, not damage as long as the fuses are the proper size. Bad 6550's will blow fuses and render the amp dead.</p>


    When I service a Leslie amp, I look at two primary voltages to determine the proper operation of the amp. First, the 6550 cathode voltage. This should be around 25Vdc. A volt or so higher is likely OK. Less is a weak tube. (unless the power supply voltages are off)</p>


    Secondly, I look at each 6550's input grid. Thid voltage should be under .1 Vdc. If it's higher, you should consider ordering a replacement set soon.</p>


    Have a look at http://www.bentonelectronics.com/serviceinfo.html under servicing the Leslie 122 or 147. </p>

    The OC3 is a regulator tube and it is supposed to flash or flicker as it does it's thing. They seldom fail.
    </p>

    George
    </p>

    Comment


    • #3
      Re: Hammond/Leslie tube question



      Thanks George, You're the man. </p>

      That benton electronics page is really good.</p>

      When you service the Leslie do you keep the amp connected to the speakers (that is, upside-down on the floor by the amp), or do you install a dummy load?</p>

      Comment


      • #4
        Re: Hammond/Leslie tube question



        Both. It depends on what I am looking for. If I am just looking at voltages for example, I don't need it connected to speakers. As long as I'm not sending signals thru it, it doesn't need a load. If I'm listening for micophonic tubes or distortion, I have it connected. Changing parts etc. would have it turned off so on the bench.</p>

        George
        </p>

        Comment


        • #5
          Originally posted by geoelectro View Post
          The only tubes that can cause damage are the 6550's in the Leslie. Actually, not damage as long as the fuses are the proper size. Bad 6550's will blow fuses and render the amp dead.</p>


          When I service a Leslie amp, I look at two primary voltages to determine the proper operation of the amp. First, the 6550 cathode voltage. This should be around 25Vdc. A volt or so higher is likely OK. Less is a weak tube. (unless the power supply voltages are off)</p>


          Secondly, I look at each 6550's input grid. Thid voltage should be under .1 Vdc. If it's higher, you should consider ordering a replacement set soon.</p>


          Have a look at http://www.bentonelectronics.com/serviceinfo.html under servicing the Leslie 122 or 147. </p>

          The OC3 is a regulator tube and it is supposed to flash or flicker as it does it's thing. They seldom fail.
          </p>

          George
          </p>
          Hi Geo, Is the ocs tube suppose to flicker all the time or just when you fire up the leslie. Mine seems to flicker lightly all the time. is this normal?
          1955 Hammond C3, 1965 Leslie 145, Trek ll Reverb, PROFKON ZD1 Overdrive Unit, Hamptone LEQ3B

          Comment


          • #6
            In Ao-28 :

            6x4 rectifier should be always checked good.

            Fails most often and could damage the Ao-28 power supply when no fuze kit is installed post stock.

            Comment


            • #7
              Boyan is right. You want to check the 6X4 in a B-3 preamp specifically for heater-cathode leakage as this is the failure mode that can cause damage. It's the 6X5 in an AO-10 preamp.

              Usually, the first tube to wear out in an AO-28 preamp is the 12AX7.

              6SJ7s in the AO-10 go microphonic more often than 6AU6s in the AO-28.
              I'm David. 'Dave' is someone else's name.

              Comment


              • #8
                The oc3 in my 147 flashes when I turn it on then glows fairly bright the rest of the time, I could discern no flickering or flashing while playing a few notes, is there something wrong with this? The 147 sound ok, though, maybe ok is ok. I am planning on getting under the hood once I am done (to whatever extent) with the 21h.

                Lewis
                Hammond '63 B3
                Leslies 21H/51C(no amp)/147(no name plate)/rotosonic 102(no horn)/31H
                Rhodes mkI stage 73
                Gibson '74 LP deluxe/'78 RD artist
                Fender '65 mustang/89 japan strat
                Guild '92 jf30/'97? jf30-12/'96 SF4
                '64 electro(ricky) es16/late 70s hoshino 2399 (gibson L5S copy)/dozen+odd others
                Fender brownface deluxe/sf mv 70s super reverb/early 80s bf,sf twin rvb/early 80s 75/'86 marshall 2203/ampeg/gibson/magna/univox/harmony/mixed slingy drum kit/mandola/sax/too many projects help!! GAS!!

                Comment


                • #9
                  Totally normal for the OC3 to flicker and flash.Predominantly blue,with a side of orange.

                  Comment


                  • #10
                    Thx Pete, no blue, mostly bright orange, a quick google image search shows both though.

                    In any case, the 147 project is on the list.

                    Lewis
                    Hammond '63 B3
                    Leslies 21H/51C(no amp)/147(no name plate)/rotosonic 102(no horn)/31H
                    Rhodes mkI stage 73
                    Gibson '74 LP deluxe/'78 RD artist
                    Fender '65 mustang/89 japan strat
                    Guild '92 jf30/'97? jf30-12/'96 SF4
                    '64 electro(ricky) es16/late 70s hoshino 2399 (gibson L5S copy)/dozen+odd others
                    Fender brownface deluxe/sf mv 70s super reverb/early 80s bf,sf twin rvb/early 80s 75/'86 marshall 2203/ampeg/gibson/magna/univox/harmony/mixed slingy drum kit/mandola/sax/too many projects help!! GAS!!

                    Comment


                    • #11
                      My OC3 - Chatham and RCA, both JAN NOS - are violet, color depends on the gas filler.
                      These are gas tubes not vacuum. Color doesn't matter.
                      It should flash on startup only, I think.

                      Very important to proper operation of the 122 type amp especially is the preamp dual triode 12au7.

                      A close to perfect match, twists more power and longevity out of the 6550 pair.

                      If you have some laying around, test them for yourself on the amp to see this phenomenon.

                      With the switching 12au7, using only one half by design, we may be more flexible.

                      My 22H was perfectly working with one on my originally found Sylvanias, that didn't work as preamp tube!
                      Last edited by ; 05-13-2013, 12:00 AM.

                      Comment


                      • #12
                        New Tubes?

                        Originally posted by johnny b3 View Post
                        What (if any) tubes should be replaced before they fail? Are there any tubes which can harm an amp or speakers when they fail?</p>

                        </p>

                        Specifically in the 147/122 leslie and also in the amps of consoles and spinets (AO-28 except for the L100?)</p>

                        </p>

                        Not totally unrelated, but I noticed that the OC3 bulb in my 147 was flickering for a few moments after startup. What exactly does the OC3 do? It is drawn as a light bulb on the schematic. When does it go bad?</p>

                        </p>

                        </p>
                        I was told that if the 6X4 tube in the organ (B3) fails it can cause other damage but I don't really know.

                        To be on the safe side I replaced all of the tubes in the organ and the 122, when the 122 amp was rebuilt by a pro. It is a bit scary how loud this setup will get, especially with all nine drawbars pulled out (122 crossover caps are also new). Seemed worth it for a 53-year-old B3. Plays really strong, loud, and clear and no bad noises.
                        T

                        Comment


                        • #13
                          The 6X4 can cause damage if the insulation between the cathode and the heater filament fails. The cathode is at 375-400V, while the heater is grounded through the heater winding's center-tap, and the cathode is wrapped directly around the heater element. Thus, the insulation between these two elements is critical. If it fails, it shorts the B+ to ground, which can damage the power transformer. I saw one like this in a repair last year. The PT was too hot to put your hand on. Luckily, I got to it in time.

                          A quality tube-tester will have a heater-cathode leakage test that can usually spot incipient 6X4 heater-cathode leakage long before it becomes a serious problem.

                          The reason for this arrangement is to avoid having to have a separate rectifier tube heater winding in the power transformer.
                          I'm David. 'Dave' is someone else's name.

                          Comment


                          • #14
                            TrekII do a nice four fuse protection device that fits to existing fixings withing the chassis. Quite expensive but well made. That would give you an extra level of protection. I had one fitted in the AO28 that I swapped for the SSP3-A.

                            Comment


                            • #15
                              Originally posted by tonewheel1966 View Post
                              TrekII do a nice four fuse protection device that fits to existing fixings withing the chassis. Quite expensive but well made. That would give you an extra level of protection. I had one fitted in the AO28 that I swapped for the SSP3-A.
                              Not as expensive as a replacement transformer...

                              Geo

                              Comment

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