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mesa rocket 44 help

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  • mesa rocket 44 help

    I have no heater VAC on v1 and v2 but have it on v3 and v4............

  • #2
    they are in DC voltage

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    • #3
      I see it now I downloaded a schematic......The amp's power tubes are redplating though I have the followimng voltages and could use some guidance troubleshooting pin 2 -11vdc pin 7 483vdc and pin 9 452 vdc

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      • #4
        Originally posted by etneccas View Post
        I see it now I downloaded a schematic......The amp's power tubes are redplating though I have the followimng voltages and could use some guidance troubleshooting pin 2 -11vdc pin 7 483vdc and pin 9 452 vdc
        can you post the schematic for us??
        If you don't know where your going any road'll take you there : George Harrison

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        • #5
          Bias sounds ok, but plate voltage is crazy high.
          https://music-electronics-forum.com/...0&d=1258342282
          Originally posted by Enzo
          I have a sign in my shop that says, "Never think up reasons not to check something."


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          • #6
            leave tubes out until you get the plate voltage right,start measuring from the HV secondary AC,then check diodes and resistors,ground connections.

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            • #7
              Mesa runs their old EL84 amps insanely hot and they eat output tubes.

              Install a bias adjust pot/circuit and set bias to proper level.
              You probably need new output tubes.

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              • #8
                Originally posted by drewl View Post
                Mesa runs their old EL84 amps insanely hot and they eat output tubes.
                Around 400V for this model as far as I know. Schematic shows 380V. He is measuring 480V plate. I can't see that as normal for this model.
                Not saying adjustable bias is not a good idea, just don't think the 480V at the plates is right. Maybe oscillation.
                Originally posted by Enzo
                I have a sign in my shop that says, "Never think up reasons not to check something."


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                • #9
                  Yeah as drewl mentioned they run them insanely hot. My DC-3 was 420VDC on the plates and only -11 as designed. No tubes would run less than 110%. The neg grid voltage needs to be at least -14 not -11 vdc thats not enough. That said 483vdc is WAY above design- unless the OP measured without the tubes in place? Bob
                  "Reality is an illusion albeit a very persistant one " Albert Einstein

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                  • #10
                    My Bad the volt measurements were without the power tubes in....Pin9 is 320vdc and pin 7 is 400vdc the functioning but is very crackily and distorted on the contour channelive swapped the preamp tubes around and still have the problem There is a copper foil shield on V2 that tube base makes a similiar sound of cracking when I chopstick it I'll try to retension the socket

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                    • #11
                      Originally posted by etneccas View Post
                      My Bad the volt measurements were without the power tubes in....Pin9 is 320vdc and pin 7 is 400vdc the functioning but is very crackily and distorted on the contour channelive swapped the preamp tubes around and still have the problem There is a copper foil shield on V2 that tube base makes a similiar sound of cracking when I chopstick it I'll try to retension the socket
                      OK thats about spec at 400vdc. The bias is just tooo low from the factory. Had the same issue with my DC-3. Any tubes I tried (even low current draw) were over 100% dissipation! Eventually modded the bias supply with help from guys here. As far as crackling- you might have bad solder joints on the sockets or just dirty/loose ones. Disclaimer- Dangerous voltages inside even unplugged. Do not go messing around inside unlerss you know how to discharge the capacitors!
                      Bob
                      "Reality is an illusion albeit a very persistant one " Albert Einstein

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                      • #12
                        Retensioned the socket and reflowed the socket pins one of them is still not shiny there is less craclking but still there V2 makes alot noise when chopstick it........

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                        • #13
                          Take a good look around. The amp gets really hot which translates into some decent temp swings on the board. I use really good light and two pairs of readers (yep, probably looks ridiculous) when hunting for cracked solder joints.
                          "Reality is an illusion albeit a very persistant one " Albert Einstein

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                          • #14
                            One thing I will mention about these is that the PI tube current affects the bias. So if you have a change in the bias condition out of the blue, it could be PI tube related.
                            Originally posted by Enzo
                            I have a sign in my shop that says, "Never think up reasons not to check something."


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                            • #15
                              That is correct, but when I have increased the bias voltage, lowering current draw, the PI cathode voltage remains the stated 3 volts.

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