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Marshall Artist, extremely low volume output.

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  • #16
    Those didn't short, they didn't even reduce resistance, they were just marked wrong.
    Education is what you're left with after you have forgotten what you have learned.

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    • #17
      I measured the heaters. Pin 9 was 5.6vac. Pins 4-5 were 1.8vac. So g1 called it there. Traced the voltages back to the power transformer. One of the heater terminals is showing 6.5 vac while the other is showing 2.5 vac. Would this mean my power transformer is defective?

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      • #18
        How did you measure?

        While I would call it unusual to get numbers like yours, all the tube cares about is the voltage across the heater terminals. So to get the BEST measurement, you'd put one probe terminal on pin 9 & the other on pin 4/5. That should be 6.3V +/-10% or so.

        If you're keeping one probe on ground and checking the two sides of the heater individually, that may explain your numbers. Also, the tubes don't really care whether that 6.3V is AC or DC.

        Justin
        "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
        "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
        "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

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        • #19
          PS: got a schematic?

          Justin
          "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
          "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
          "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

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          • #20
            Schematic : Marshall_artist_30w_3203.pdf
            Experience is something you get, just after you really needed it.

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            • #21
              Yes, you were right. I still had one probe connected to ground. I have sine placed one probe on p9 and one on p4-5 and have a reading of 6.3 vac. This is the schematic i am using: https://drtube.com/schematics/marshall/3203pwr.gif

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              • #22
                The problem still persists and i continue to have that high voltage reading on p1

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                • #23
                  Originally posted by mfreqmaster View Post
                  PI voltages: p1 434v, p2 7v, p3 31.5v, p6 221v, p7 18.5v, p8 31.5v

                  I'd expect pin 2 to read about the same as pin 7. This makes me suspect that C12 is leaky. Try disconnecting the inner conductor of the input cable that goes to it and remeasure pin 2 and pin 7. BTW the grid voltages are obtained measuring between cathode and grid to avoiding loading the grids with your meter and getting silly results.
                  Experience is something you get, just after you really needed it.

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                  • #24
                    Measuring the 6.3V at the socket terminal is just the first part. It doesn't necessarily mean the voltage is getting to the tube pins. That is why I asked if you can see both sides lit. You might have to turn off the lights.
                    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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                    • #25
                      I turned off the lights and looked at the 12ax7. It appears to be glowing on both sides of the tube.

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                      • #26
                        Ok. I'd suspect the coupling cap like nick suggested, but the plate voltage is high, rather than low which is what I would expect from a leaky cap.
                        So still suspicious of that side of the PI tube not conducting. Have you checked the resistance of the pin1 plate resistor?
                        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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                        • #27
                          Originally posted by g1 View Post
                          Ok. I'd suspect the coupling cap like nick suggested, but the plate voltage is high, rather than low which is what I would expect from a leaky cap.
                          So still suspicious of that side of the PI tube not conducting. Have you checked the resistance of the pin1 plate resistor?
                          Quite right. I see I missed the high voltage on pin 1 - thx. The cathode is 31.5V and the total tail resistance is about 15K so the tail current is 2mA. 2ma across the 100K on pin 6 drops 200V so there really is no current at all in that pin 1/2/3 section. Could the socket be bad so that pin 3 is open? Pin 2 is still odd.
                          Experience is something you get, just after you really needed it.

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                          • #28
                            Sorry for the delayed response. Hobbyist here with limited time to devote to this. I wiggled the tube socket while on and got a huge change in hum volume/static. So I strongly suspect the 12ax7 socket is bad and not allowing the tube to conduct. I've got a spare. Problem is on the 3203 the socket is riveted in. Any suggestions on how to remove it?

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                            • #29
                              Originally posted by mfreqmaster View Post
                              Sorry for the delayed response. Hobbyist here with limited time to devote to this. I wiggled the tube socket while on and got a huge change in hum volume/static. So I strongly suspect the 12ax7 socket is bad and not allowing the tube to conduct. I've got a spare. Problem is on the 3203 the socket is riveted in. Any suggestions on how to remove it?
                              With a drill a little smaller than the rivet, drill out the center then use a punch to knock the rest out. Rivet gun at the home depot or pawn shop and some rivets is all you need. I'm a tool guy so if I see a chance for a tool I get it. It's nice to be able to have the right tool when you need it.

                              nosaj
                              soldering stuff that's broken, breaking stuff that works, Yeah!

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                              • #30
                                Even though I have rivets and a rivet gun at work I would just use screws and nuts for replacing a socket.

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