Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

(Another) Mojotone 5F1. Troubleshooting Time.

Discussion in 'Shock Brother's DIY Amps' started by DavesPlanet, Dec 4, 2017.

  1. DavesPlanet

    DavesPlanet TDPRI Member

    26
    Oct 18, 2013
    Bangkok

  2. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    Can you giv voltages at each pin on the tubes

    V1 12ax7

    V2 6v6

    V3 5y3

    Observe while probing the plates and grid on the output and pre amp tubes, they should produce popping/scratching sound at the speaker, volume set abou 1/3 to 1/2

    kob khun krup:)
     
    Last edited: Dec 4, 2017
    DavesPlanet likes this.

  3. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    I just saw your voltages. Looks like you should be hearing something. Do the pop test, if you hear pop sound on the plates and grids then your input jacks are suspect. the 33 and 68k looks good... what about tip to ground at each. It's hard to tell but in the pic it looks like the shunt is still touching the tip which would dump the signal to ground=silence.
     

  4. Meteorman

    Meteorman Tele-Holic

    582
    Dec 23, 2012
    State College PA
    How is your speaker jack grounded? Is the 22k NFB resistor continuous with ground - the “Y” in your green circle? It shouldn’t be.
     

  5. dan40

    dan40 Tele-Holic

    626
    Aug 19, 2015
    Richmond Va
    I recently completed a Fender build in which I had zero sound from when I first fired it up. Turned out that the input jack switch was not opening properly when inserting my usual guitar cable. Some cable ends are slightly larger than others so occasionally these Switchcraft jacks do not fully open when inserting your cable. Try wiggling the cable around at the input and output jacks while strumming a cord. If you hear momentary guitar sound when doing this, you will need to slightly bend the switching contact blade on the offending jack to help it open fully.
     

  6. DavesPlanet

    DavesPlanet TDPRI Member

    26
    Oct 18, 2013
    Bangkok
    I recently found the Fender Amp Clone Club group at Facebook and had been discussing my build there some. Thankfully, one of the members emailed me the solution, which I read when I woke up this morning. I'd made a silly newbie mistake. He'd scanned the resistors in my pictures and found I'd put 100kΩ ones where 100Ω ones were supposed to go. (I'd swapped the artificial center tap resistors resistors on the pilot light with the 2 that go to the 12AX7.) It was a hassle to unsolder them and put them where they were supposed to go, but as soon as I did, IT WORKED! (I suppose it's also possible someone at Mojo put the resistors in the wrong compartments of the component box? If so, I should have caught it when I checked their values, which I did at the beginning of the build....)
    So, I think I'll just enjoy it for a bit and take a short break. Then I'll probably consider some of the mods that everyone suggests for the 5F1. :)
    Still, thanks to y'all at TDPRI for taking the time to examine my build and comment. I appreciate it. ;-)
     
    Fiat_cc likes this.

  7. Kevin Wolfe

    Kevin Wolfe TDPRI Member

    Age:
    59
    7
    Jun 13, 2017
    Lakeland FL
    You can't trust 'em. Get yourself a resistor chart and read the color codes. Then verify them with a meter.
     

  8. keithb7

    keithb7 Friend of Leo's

    Age:
    46
    Jan 9, 2010
    Western Canada
    There are a few of us Tdpri regulars, who are also members of the Facebook Fender Clone Amp Club.

    I actually created the group and I am the admin. I am proud to hear you got the help you needed. Here or there, we’re all sharing our passion for tube amps.
     
    coldengray and DavesPlanet like this.

  9. DavesPlanet

    DavesPlanet TDPRI Member

    26
    Oct 18, 2013
    Bangkok
    I'm a newbie, but I watched some vid's on resistor colors (BBRYGBVGW), and the first thing I did was check the values with what they were documented to be by Mojo. They were all well within tolerance. ;)
     

  10. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    I didn't know you had made a group for those. I'll have to stop by and join up!
     

  11. DavesPlanet

    DavesPlanet TDPRI Member

    26
    Oct 18, 2013
    Bangkok
    I just recently found the FB group. It's kinda interesting the different feeling between it and BBS-type forums like this.
    Though I now see there is some overlap in membership between here and there...for tdpri folks who may be interested, here's a vid I just made demo'ing the Champ and another new piece of gear, the Fryette Power Station 2, which is a 'reactive attenuator' and more. (An 'apartment recording' solution.)
     
    keithb7 likes this.

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