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Please help. Troubleshoot first build?!?!?

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  • #16
    Originally posted by hesamadman View Post
    I dont get anything between 2 and 3 or 7 and 8
    On V3, you should find that pin 2 is about one volt less that pin 3 and similarly for pins 7 and 8. Earlier said the measurement was 12VDC on pin 2, 41VDC on pin 3 and 12VDC on pin 8. These measurements are not consistent based on the plate voltages. Go do it again. There is no room for inaccuracy in any of this.

    Assuming the measurements are off, my guess is this stage is fine based on the touch & pop 'tests' and good plate volatges. Have you checked the wiring esp volume and tone stack yet?
    Experience is something you get, just after you really needed it.

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    • #17
      Originally posted by hesamadman View Post
      guessing third preamp tube isnt getting what it needs?

      1st preamp tube-

      pin 1- 260 vDC
      pin 2- ~0
      pin 3- 2.9
      pin 4 and 5- 2.7 vAC
      pin 6- 220vDC
      pin 7- ~0
      pin 8- 2.04
      pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC

      2nd preamp tube-

      pin 1- 170 vDC when my lead touches this I hear a noise in the amp.
      pin 2- ~0
      pin 3- 1.6
      pin 4 and 5- 2.7 vAC
      pin 6- 319vDC
      pin 7- 170
      pin 8- 180
      pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC

      3rd preamp tube-

      pin 1- 234 vDC when my lead touches this I hear a noise in the amp.
      pin 2- 12 is this low?
      pin 3- 41
      pin 4 and 5- 2.7 vAC
      pin 6- 220 vDC
      pin 7- 13
      pin 8- 12
      pin 9 around 2.7 ACROSS BOTH pin 9 AND pin 4/5 I GET ABOUT 5.9 vAC
      I built and play this exact same amp and layout.
      V3 Pin 3 and 8 should read the same they should be strapped together.
      T
      ** Nick already said this similarly
      V3 looks similar to my voltage chart except for pin 8
      This is my working 2204
      V3 12AX7, 222V +DC, 14.3V +DC, 41.8V +DC, 3.31 AC, 3.31 AC, 208V +DC, 14.2V +DC, 41.8V +DC, 3.31 AC
      Last edited by big_teee; 08-05-2013, 08:29 PM.
      "If Hitler invaded Hell, I would make at least a favourable reference of the Devil in the House of Commons." Winston Churchill
      Terry

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      • #18
        Check the wiring of the input jacks. This will also check that any coax is not shorted.

        Refer to the attached pics. Make sure the power is off for these tests.

        With no guitar plugged in:
        Pin 7 of 12AX7 should measure 68K to ground.
        Points A, B, C, D and E should be grounded. Your meter should read 1 ohm or less.
        Turn the Volume control all the way up. Pin 2 of the 12AX7 should measure about 330K ohms.

        Plug a guitar cord into the HI input jack. Leave the guitar end of the cable not connected or touching anying.
        Pin 7 of 12AX7 should measure about 1 Megohm to ground.
        Point A should measure 1 Megohm to ground.
        Points B, C, D and E should measure about 1.5 Megohm to ground.
        Now measure from the unconnected tip of the guitar cord to pin 7 of the 12AX7. It should measure 68K ohms.
        Measure from the tip of the guitar cord to the shield at the guitar end. It should measure 1 Megohm.

        Now unplug the cord from the HI input and plug it into the LO input.
        Points D and E should measure about 1.5 Megohms to ground.
        Points A, B and C should be grounded.
        Measure from the unconnected tip of the guitar cord to pin 2 of the 12AX7. It should measure about 470K ohms when the Volume control is all the way up.
        The tip of the guitar cord should measure less than 1 ohm or so to points D and E.
        Attached Files
        WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
        REMEMBER: Everybody knows that smokin' ain't allowed in school !

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