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New 5E3 Help please?

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  • New 5E3 Help please?

    Hi...just built a Mojo kit and have some problems.
    I bought the Mojotone Kit because they had a good sale on....considerably cheaper than anywhere else and I got a damn nice custom tolex cab with it. I decided to buy the Tube Depot board and use it. I also upgrade the Mojotone caps with a side of Dijon. I wanted to change the layout a bit so I could install a Voltage regulator in the front panel fuse hole. I also added a switch on the back for Ohm selection of the output jacks. I also plan on putting another switch there for the negative feedback mod.
    When I did the first power up, all was well with no shorts and dim bulb working as it should with rectifier tube and preamp tubes installed...good. However when I put the power tubes in, the dim bulb tester glows medium bright and stays lit. I have a low volume guitar sound, and there is no overdrive. Checked the wiring over and over, and all seems well.
    I measured the VAC across each end of the heater winding (e.g.; i.e.: between pins 4-5 and 9 of the pre-amp tubes, and between pins 2 and 7 of the output tubes Here are my voltages with all tubes out;
    V5 2&8=5.4vac 4&6=812vac
    V4 & V3 2&7=7vac
    V1 & V2 Heaters= 6.9vac

    All tubes in, rectifier V5;
    225Vac on pins 4 and 6 and 232VDC on 8 and 2

    Filter caps;
    242 210 and 183VDC from edge of board inward









    Any comments are greatly appreciated. Thanks
    Attached Files

  • #2
    Can you provide any Volts dc readings.
    I don't quite get all of the Vac readings (why?)
    If you have good Vdc readings (they will be low because of the lamp) get rid of the lamp (it is limiting the current)

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    • #3
      OK I pulled the bulb and and took VDC readings.
      V1
      Pin1 142
      Pin3 0.26
      Pin6 138
      Pin8 0.24
      V2
      Pin1 127
      Pin3 0.52
      Pin6 141
      Pin8 21.5
      V3
      Pin3 217
      Pin4 190
      Pin5 0
      Pin8 8.6
      V4 is identical to V3
      Thanks for the help!

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      • #4
        My question would be 'why is the B+ voltage so low?'
        Bad rectifier?
        Something miswired?
        How about measuring B+ with the tubes removed.

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        • #5
          Turned out to be a bad Variac...fakt

          Comment


          • #6
            Oops.
            It is not a bad idea to test 'everything' when trying to track down a problem.
            AC source voltage, meter leads, jumper leads, the meter itself.
            Glad that you found it!

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            • #7
              So I have found out the hard way. That's alright. (listen to yourself first, and others second, is the lesson learned)I tested everything and found out that the variac is alright after all. Here I was blaming it on the Chinese. LOL The real culprit was the cheap volt meter I had plugged into it. O K it is was made in China also, but isn't almost everything these days.
              I will go back to plan A and rebuild this one more time with the Tube Depot board and mods I had planned. Just gotta get some more solder and wire, and do it again.
              The new amp sounds great, but has to be turned up way to loud for that singing overdrive blues tone. Even with a NOS 5y3. Everyone says these amps sound better with single coil pups, but I sure like my bucker axes plugged into it. I have lots of playing to do just to break in the speaker, which I may upgrade down the road. It is also way to bass heavy. I will install a Mini Watt VRM, and change a couple of coupling caps to lower values. Hopefully this will rectify these problems. By the time the smoke clears on this build, I probably could of bought a slightly used Fender Deluxe Reverb which was what I was wanted to begin with. And may have been a better choice for my playing needs. However this has been a great learning experience and has me planning for another amp build next winter.
              Just gotta get some more solder and wire, and do it again.

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