This week in "What do you think of this wiring job?" features an 18 watt Marshall.

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by GuitarInnovations, Dec 24, 2019.

  1. xtian

    xtian Member

    Messages:
    2,152
    Joined:
    Dec 15, 2010
    Location:
    NorCal
    If I squint....it sounds pretty good.

    Power input wiring is messy, and I can't tell exactly, but looks like hot is fused, then goes to PT, while neutral is switched? That's not good--puts hot on the PT even when switch is in OFF position. Is chassis properly grounded to earth? Is there a stray red wire that goes nowhere?!?
     
    pdf64 likes this.
  2. VICOwner

    VICOwner Supporting Member

    Messages:
    1,384
    Joined:
    Jun 14, 2017
    Location:
    Leesburg, Georgia
    In all that craziness, they did braid the secondary of the output transformer. If they had kept up after that it would be better but it could be worse. How does it sound?
     
  3. Vanyu

    Vanyu Member

    Messages:
    739
    Joined:
    Oct 11, 2015
    Really doesn't look too bad, definitely better than what you would've gotten in a 70's Fender wiring job! I like the way the preamp is grounded with the single bus across the front of the board, less noise than multiple chassis grounds IME. Front control wiring could've been done a little better, those can be braided (and heatshrinked for added cleanliness) too for noise suppression, but that's not a hard project to do yourself. Tube wiring routing looks okay, grid wires look like they're nice and out of the way, but I'd prefer to see those taped or gooped to the chassis. Power supply area looks a little goofy, some of those wires definitely need a haircut and braid and schematic once over, but I doubt that part of the amp would contribute to noise or oscillation, it's just ugly!

    All in all looks like a solid build, spend a couple hours braiding those front control wires and trimming some excess wire here and there and it will be whisper quiet, but it really shouldn't be too bad as-is.
     
  4. oneblackened

    oneblackened Member

    Messages:
    790
    Joined:
    Jan 6, 2019
    Location:
    Boston, MA
    Not bad, but not amazing. @Vanyu hit it on the head.
     
  5. pdf64

    pdf64 Member

    Messages:
    6,567
    Joined:
    Aug 9, 2008
    Location:
    Staffordshire, UK.
    Err, safety first! Until there's a decent photo that shows there's reasonable chance the chassis (and hence any guitar plugged into it) is properly grounded, the advice has to be not to touch it with a 10 foot pole. A wooden one.
    The white neutral wire from the IEC inlet looks to have a a significant burn mark (ie probably due to careless wielding of the soldering iron).
    Bearing in mind that wire may often carry full mains voltage due to miswired wall outlets, that really should be replaced. Hence it may not bode well for the builder’s qc.
     
    Last edited: Dec 26, 2019
    xtian likes this.
  6. aynirar27

    aynirar27 Notable Member Gold Supporting Member

    Messages:
    31,254
    Joined:
    Jul 15, 2011
    Location:
    Great Barrington, MA
    Is the mains grounded anywhere?
     
  7. Jeff Gehring

    Jeff Gehring Silver Supporting Member

    Messages:
    5,381
    Joined:
    Jan 17, 2008
    Location:
    Kansas City area
    Ahem. I believe you meant to say 'Am the mains grounded anywhere'. Grammar are important.

    I think that cheesy snap-in IEC receptacle is hiding the ground wire (I hope). Just a matter of time until the amp owner goes to pull out the AC cord for transporting the amp, and the whole dang socket and wiring come with it. If I'm doing an IEC inlet, I always get the metal ones that attach with machine screws.
     
    gght, 79Stone1, pdf64 and 1 other person like this.
  8. aynirar27

    aynirar27 Notable Member Gold Supporting Member

    Messages:
    31,254
    Joined:
    Jul 15, 2011
    Location:
    Great Barrington, MA
    its the mains socket ground anywhere? :)
     
    Jeff Gehring likes this.
  9. 79Stone1

    79Stone1 Member

    Messages:
    230
    Joined:
    Aug 10, 2011
    Location:
    WA State
    :rolleyes::D
     
    aynirar27 likes this.
  10. Winnie Thomas

    Winnie Thomas Silver Supporting Member

    Messages:
    613
    Joined:
    Nov 11, 2006
    Location:
    Cochise, Arizona
    Whats with the two resistors going to the EL84s? unless the resistors on the board go to ground instead of B+ they should connect to the resistors that go to ground at the opposite end of that section.
     
  11. Vanyu

    Vanyu Member

    Messages:
    739
    Joined:
    Oct 11, 2015
    The small resistors are grid stoppers and large resistors are screen grid stoppers. The two 470K resistors that conjoin right before the grid stoppers are the grid leaks going to ground (or to -biasV in fixed bias). The resistors at the other end of that chunk are the P.I plate resistors, and it looks that they make their way over to the P.I under the board and connect to the plates through the blue and grey wires that seemingly terminate to nothing from the top. Looks to be a slick way of minimizing the wire run for the EL84 grids.
     
  12. Winnie Thomas

    Winnie Thomas Silver Supporting Member

    Messages:
    613
    Joined:
    Nov 11, 2006
    Location:
    Cochise, Arizona
    That's what I thought might be the case, but it's unusual.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice