New 5E3 Build Loud hum and pop turning off

Discussion in 'Shock Brother's DIY Amps' started by timewaster1700, Aug 5, 2019.

  1. timewaster1700

    timewaster1700 Tele-Meister

    Feb 17, 2016
    Well here we go, another 5E3 I need help thread. Sorry. This is my second amp build (first was a 5F11). Followed @robrob 's startup procedure and everything went well. Voltages are all pretty close to those on his layout drawing on his website. I haven't plugged in a guitar yet, but with the amp on and the volumes all the way down it hums pretty loud. It takes a bit of time for the hum to build up (gradually gets louder, almost like charging up). Turning either of the two volume pots up seems to have no effect on the hum until you hit about 80% then it switches from hum to a light scratchy/fizzy noise.

    I read some threads on this forum and have tried moving around wires and making sure all the preamp wires are separate from one another and separate from the heater wires. I removed V1 and it was a bit louder hum maybe? I removed V2 and it seemed to take longer for the hum to build up but it was just as loud once it did.

    I used the modified mojotone layout attached expect I have not run any wires to the mute switch yet so you can ignore that. The only mods really are just bleader resistor for filter caps, backup rectifier diodes, and screen resistors.

    Any help would be appreciated.

    UPDATE: Plugged my guitar in. Sounds normal playing the guitar. Wow this thing has some sweet overdrive with a humbucker bpup. Perfect China Grove sound. Noticed my pilot light is blinking on and off so that's not good. Must have a bad connection to that. The hum doesn't seem very loud with the guitar plugged in, especially compared to playing volume so maybe I don't need to worry about it for now. But I do need to fix the pilot light wiring. Something is wrong there.

    Mojotone layout modified.jpg IMG_5842.jpg IMG_5843.jpg IMG_5844.jpg IMG_5845.jpg
    Last edited: Aug 5, 2019
  2. BigDaddy23

    BigDaddy23 Tele-Holic

    Jan 4, 2019
    Congrats on a really neat build, mate.

    A couple of things I note from your pics:

    The solder joints on your indicator light and fuse holder look like they need to be reflowed. (Last pic).

    Check all your joints and reflow anything that catches your eye. I'd suspect a dodgy ground with what your described. Reflow the shorting and ground lug connections on the input jacks...this might explain why it hums without the guitar plugged in. Also, The white ground wire running between the input jack and ground bus could go straight into the eyelet instead of the j-hooked to the bus bar. You are relying on that joint for your preamp ground.

    Shouldn't be to hard to track down! Love my 5e3!!
  3. corliss1

    corliss1 Friend of Leo's Platinum Supporter

    Sep 13, 2008
    Lansing, MI
    If it sounds normal when you have a guitar plugged in that would tell me there is an issue with the way the shorting inputs are wired, so check that area.

    Looks like VERY clean work, although you seem to be a little light on the solder. Don't be afraid to fill the holes completely.
    sds1 and SacDAve like this.

    DADGAD Friend of Leo's

    Mar 18, 2003
    On the output tube filaments, verify that pin 2 of the first 6V6 is wired to pin 2 of the second tube. Pin 7 to 7 as well. If not, it will hum.

    To eliminate switch pop, install a .01mfd, 1KV capacitor across the switch contacts.

    Good luck!
  5. Paul G.

    Paul G. Friend of Leo's

    Mar 17, 2003
    Rhode Island
    First place I'd look is the input wiring.
  6. Commodore 64

    Commodore 64 Friend of Leo's

    Mar 1, 2010
    Kent, OH
    Those 6.3v lamps annoy me so much, always burning out and flickering as the Tx sags, I've taken to using 120v Neons instead.

    Plastic zip tie on the 250 Ohm cathode resistor might melt, Good choice on 10W cinder block, though.

    Lot of your front panel stuff is light on solder. I like nice shiny blobs. Your input jacks especially could use some more solder.

    I like to hang my input grid resistors right off the tube socket, close to the pin as possible and use coax (for the shielding). But there's 1000's of amps that don't do (or need) that.

    Looks like your plate resistors are metal oxide? I'd use carbon or metal film there.
    Last edited: Aug 5, 2019
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