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First build problems - Mission 5E3

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  • First build problems - Mission 5E3

    Hi all,

    I'm having some trouble getting my Mission 5E3 kit up and running. As of right now it turns on with no smoke or explosions, all the tubes light up, but there is no sound (not even hiss) and the tubes seem to be REALLY hot (you'll burn yourself if you touch them). I can make some noise come out if I whack the strings very hard, or plug in a cable with no guitar and touch my finger to the tip.

    I've taken some voltage readings, and some of them seem WAY too high. I can't for the life of me figure out why! Here are the voltages, taken with the black lead on my meter clipped to the chassis:

    NO TUBES INSTALLED:
    V5 (Rectifier):
    Pin 2 - 5.5VAC, 9.5VDC*
    Pin 4 - 340VAC
    Pin 6 - 340VAC
    Pin 8 - 10VAC, 9.5VDC*

    V4 and V4 (voltages were the same):
    Pin 2 - 3.4VAC
    Pin 3 - 9VDC*
    Pin 4 - 9VDC*
    Pin 7 - 3.4VAC

    V2 and V1: (voltages were the same):
    Pin 1 - 6.8VDC*
    Pin 4 - 3.4VAC
    Pin 5 - 3.4VAC
    Pin 6 - 6.8VDC*
    Pin 9 - 3.4VAC

    * = On these pins the voltage continued to drop while the amp was on, so you can see the value decreasing as I worked through the pins from V5 to V1.

    RECTIFIER INSTALLED:
    V5 (Rectifier):
    Pin 2 - 22VAC, 462VDC
    Pin 4 - 341VAC
    Pin 6 - 341VAC
    Pin 9 - 22VAC, 462VDC

    V4 and V3 (voltages were the same):
    Pin 2 - 3.4VAC
    Pin 3 - 22VAC, 458VDC
    Pin 4 - 22VAC, 458VDC
    Pin 7 - 3.4VAC

    V2 and V1 (voltages were the same):
    Pin 1 - 21VAC, 450VDC
    Pin 4 - 3.4VAC
    Pin 5 - 3.4VAC
    Pin 6 - 21VAC, 450VDC
    Pin 9 - 3.4VAC


    One thing that I noticed while I was taking the readings is that on Pin 3 of both 6V6s (where the OT wires connect) I could make the meter jump back and forth between 22VAC and 340VAC, and when I touched the terminals with the probe it would sometimes make a loud racket through the speaker.

    Also, I have not wired up the 4 Ohm tap of the OT, only the 8 Ohm tap. Not sure if that makes any difference (the mission instructions show you to just hookup the 8 Ohm).

    So what do you guys think? I'm really lost and frustrated at this point. I have lots of experience building and doing very simple mods to pedals, but this is a whole 'nother animal. I just can't figure out how to troubleshoot this thing! I'm not even sure I'm using the correct method of measuring the voltages, as I can't find any instruction online on how to do simple stuff like that. As you can tell, I feel like I'm in a bit over my head.

    Thanks for your help!

  • #2
    Tubes have internal resistance, try measuring with tubes installed. Are B+ and plane high to? I didn't quite get the part where you talked about jumping voltages... Do you have AC where you shouldn't that could spell bad filter caps or bad wiring in the filter.

    Edit, take some old tubes when you measure, so you don't end up frying new once.
    In this forum everyone is entitled to my opinion.

    Comment


    • #3
      With the "jumping voltages" on Pin 3 of the 6V6s: basically, if I moved the probe slightly while touching either the solder terminal (inside the chassis) or the pin socket (outside of the chassis) I could get the meter to read either 22VAC or 340VAC.

      So are those voltages I took without all the tubes installed kinda worthless then?

      Comment


      • #4
        I don't have a masters degree in measurements taken without tubes... Layman's answer, yes to me they would be useless. ;-)

        Don't nudge the thing you're probing. Get a alligator or something similar and hook it firmly. If you feel unsure around the socket take the readings on the board instead.
        In this forum everyone is entitled to my opinion.

        Comment


        • #5
          Have you contacted Bruce?
          "In theory, there is no difference between theory and practice. In practice there is."
          - Yogi Berra

          Comment


          • #6
            Haha, okay, I will take voltage readings with the tubes in.

            Haven't contacted Bruce yet. What's the best way to get in touch with him? It looks like he seems to post here fairly often...

            Comment


            • #7
              I think Bruce has his phone number on his posts.
              "In theory, there is no difference between theory and practice. In practice there is."
              - Yogi Berra

              Comment


              • #8
                It works!

                I got it working, and it sounds SWEET!

                A forum member on TDPRI took a look at a pic I posted and immediately noticed I had made a mistake in wiring one of my resistors. Doh! I don't know why I waited so long to get another set of eyes on this thing.

                Anyway, I fixed the mistake and it fired right up. Wow! What a great sounding amp!

                I checked some of the voltages, and they are MUCH lower now. Have had the amp running for a few hours with no smoke or flames.

                Thanks for the help and advice everyone!

                Comment


                • #9
                  Argh, I missed out on the, did you triple check every thing.

                  By the way. I hope your friend told you to be careful, amplifiers can be very addictive.
                  In this forum everyone is entitled to my opinion.

                  Comment


                  • #10
                    Sometimes a picture is worth a thousand words....
                    Bruce

                    Mission Amps
                    Denver, CO. 80022
                    www.missionamps.com
                    303-955-2412

                    Comment

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