JTM45+ Clone Build Help Request

Discussion in 'Amps and Cabs' started by garret, Feb 4, 2015.

  1. garret

    garret Member

    Messages:
    889
    Joined:
    Oct 2, 2014
    Location:
    Michigan
    Looking for a bit of help from some of the very sharp individuals on TGP.

    Put together a JTM45+ clone build from Tube Depot and was in the power up phase. All voltages are reading correct for the preamp circuit except for the cathode triode voltage on pins 3 and 8 of V3. The assembly manual states it should be 35VDC but it's actually measuring 85.6VDC.

    Tube Depot Layout;
    https://d1sjrnpi226dnf.cloudfront.n...es/jtm45plus_wiring_diagram_v4.pdf?1391458164

    Schematic;
    https://d1sjrnpi226dnf.cloudfront.net/spree/attached_files/jtm45plus_schematic_v4.pdf?1391458123

    I wrote an email to Tube Depot but from what others are saying, they aren't much help.

    Voltage Readings;
    T6 = 2.0VDC
    T4 =1.0VDC
    T18 = 1.1VDC
    T20 = 157.6VDC
    T32 = 50.3VDC
    T34 = 86.1VDC
    T38 = 55.1VDC
    T36 = 85.6VDC


    The only altercation done to the schematic is a ppimv type 2 kit from Triode Amps.

    Appreciate any suggestions.

    [​IMG]
     
  2. DrainBamage

    DrainBamage Member

    Messages:
    2,159
    Joined:
    Sep 23, 2011
    I would make sure the cathode resistor and tail resistors are the 470 ohm (not 470k) and 10k
     
  3. garret

    garret Member

    Messages:
    889
    Joined:
    Oct 2, 2014
    Location:
    Michigan
    Looking at a photo on my phone, the 470 and 10k appear to be correct. Will reflow the turret and pull measure the values if it's still 85VDC.

    10k =brown, black orange with gold tolerance band
    470 =yellow, violet, black, black with brown tolerance band

    Thanks for the help DrainBamage.

    EDIT: Found the issue, forgot to tie C20 (cap on the presence knob) to ground.
     
    Last edited: Feb 4, 2015

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