A(nother) Clean 5e3 build.

Discussion in 'Shock Brother's DIY Amps' started by Doctor49, Dec 19, 2019.

  1. Doctor49

    Doctor49 TDPRI Member

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    Hi,

    This is my first thread here although I have been digging through looking for clues about this build problem.

    Its a Mojotone 5e3 kit, loud and clean all the way up to 12 on tone, vol 1 and vol 2, with Tele, 335 or PRS Custom 24 inputs. This seems to happen sometimes according to what I have read, but I didn't find any specific reason yet.

    It has the MJ international PT using the 240VAC tap as Thailand claims 220v, produces unreliable 230v and 240v gets about the right voltages.

    When chopsticking, I found all input circuitry to the V1 socket was microphonic.

    A switchcraft socket that had a flaky short was fixed with pliers and I redid the input sockets connections just in case.

    Two independent sets of eyes did checks that passed on components in correct locations and all values ok.

    I reflowed all the connections on the fibreboard. All continuity checks out and resistance checks across the joints OK

    The only thing left from chopsticking is a PING when V1 is tapped - nothing from the others at all.

    Some build pictures are attached. I have more at various stages and various close ups.

    The tube and B+ measured values are attached, all tubes in and all pots at zero.

    I didn't get a speaker yet so I am testing through a Celestion G10N-40 that I have run for several years on my Blackstar 5 stack.

    I am limited in test gear to lamp bulb limiter, Fluke DMM, a8R dummy load and one of my wife's chopsticks.

    I would like to learn more about this and look forward to the benefit of others experience here.

    Thanks!

    (I'm building a monorail system at work so may be slow to reply sometimes. Yes, its a Simpsons Project)
     

    Attached Files:

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  2. D'tar

    D'tar Friend of Leo's

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    A tweed deluxe without distortion..... Call the RTP!!!

    Your build looks pretty solid and voltages are within reason. Make sure you have the 12ay in V1 and the AX in V2. INput jacks, speaker connections and/or ground connections are alway the usual suspects. Close up pics in these areas may help. What power tubes are you using?
     
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  3. King Fan

    King Fan Poster Extraordinaire

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    What D'tar said. :) And yes, the build does look nice. Your pinging on V1 also makes me wonder if you might have a bad tube there. Cay you try another 12AY7?
     
  4. Snfoilhat

    Snfoilhat Tele-Afflicted

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    Easy troubleshooting for input jacks that's related to the symptom of low gain:

    https://robrobinette.com/How_Fender_Input_Jacks_Work.htm

    This is a good read with a lot of detail. If you only need the briefest version to apply to your situation, the idea is to insert your instrument cable into each of your four input jacks, and measure the resistance from tip to sleeve on the cable plug where your guitar would go. The two high inputs have a particular resistance, the two low inputs have a different resistance. The next step is to measure from the tip to the tube socket pin for the first triode's grid. Again, the two high inputs have one resistance, the two low inputs have a different resistance.

    If your jacks have any wiring issues, this is an easy way to catch it that doesn't rely on visual inspection.
     
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  5. Doctor49

    Doctor49 TDPRI Member

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    Thanks!
    I have V1 12ay and V2 ECC83S (came with the kit as 12ax equivalent) and 6v6 power tubes (measurements as in the attached sheet), all JJs.

    I have spare 12ax (Sovtek and EH) which I have rotated through with no change.

    I don't have an alternative 12ay right now, but I did try a 12ax in V1 just to see. It got louder but still clean. I will get another 12ay when I get the chance.

    I checked out the input resistances also.

    I'm starting to think I need the necessary equipment to follow the signal path through..........


    "A tweed deluxe without distortion..... Call the RTP!!!"
    D'tar, better to call someone you know!
     
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  6. Doctor49

    Doctor49 TDPRI Member

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    Update:
    I tried a new 12ay7. Subjectively maybe a bit louder but nothing in the crunch/overdrive area.

    Measuring the input jack configuration resistances (power off), I got the following:

    Nothing plugged in V1 Pins 2 and 7 to ground 33.9K.

    With open cable plugged in (reading V1 pins 2 and 7 to ground):
    With an open ended cable plugged into Normal input:
    input 1 reads 1005k on pin 2 and 33.9k on pin7
    input 2 reads 67.3k on pin 2 and 33.9k on pin7

    With an open ended cable plugged into Bright input:
    input 1 reads 33.6k on pin 2 and 974k on pin7
    input 2 reads 33.6k on pin 2 and 67.4k on pin7

    With open cable plugged in (reading open end tip to sleeve):

    #1 input reads 135.2k Normal and 1134.4k Bright
    #2 input reads 937k Normal and 968k Bright

    With open cable plugged in (reading open end tip to V1 pins 2 and 7):

    With an open ended cable plugged into Normal input:
    Input 1: 33.65k on pin2 and 1004k on pin 7
    Input 2: 67.2k on pin2 and 167.9k on pin 7

    With an open ended cable plugged into Bright input:
    Input 1: 977k pin 2, 33.9k pin 7
    Input 2: 168.9k pin 2, 68.0k pin 7

    This does not look right.
     
  7. BigDaddy23

    BigDaddy23 Tele-Holic

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    I reckon it would be useful to make a voltage chart and compare that to the schematic values. Post em up here for the learned folks to discern.
     
  8. Tom Kamphuys

    Tom Kamphuys Tele-Holic

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    I sat down and looked at your measurements. I found it hard to decipher just what you measured as there are quite some perturbations of variables (which it seems like you dutifully measured).

    I decided to approach it from a theoretical point of view and realised there are only three input situations: 1, 2 and nothing (let's forget the jumpering option)

    You measure either grid-ground or tip-sleeve.

    I come to the following old fashioned pen-and-paper chart of the theoretical resistance measurements (underlined):
    IMG_20191222_130202121.jpg

    All in Ohms of course.
    Edit: And the tip-sleeve annotation is a bit misleading with nothing in the inputs :D
    Edit2: Drawing III wrong. Grid-ground value correct. Until further notice...

    I'll leave the mapping to your table up to you (or someone else). At least for now...
     
    Last edited: Dec 22, 2019
  9. Doctor49

    Doctor49 TDPRI Member

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    Thanks. I can do that on the posted measurements in my first post if it helps.


    TBH I measured all the various scenarios suggested in another thread!
    Thanks very much for suggesting that representation. I'll map and get back to you.
     
  10. King Fan

    King Fan Poster Extraordinaire

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    I see you have a nice voltage chart attached as a PDF in the OP. PDFs are poorly handled here -- which limits views -- so far yours seems to have 9, including 2 by me. :)

    FWIW I make a voltage table in Excel; then a screen grab + crop as a PNG or JPG will post inline and get more views.

    EDIT: This is a nice reference from our old friend Telenut62, and also a nice way to do a visual voltage table.

    Telenut_5e3_voltages.png
     
  11. King Fan

    King Fan Poster Extraordinaire

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    Also, since both channels (as @Snfoilhat said) have the same input resistances, you're looking for just four values. Our friend @D'tar showed me this, IIRC. If I got the numbers wrong, it's on me, not him.

    For both channels,
    Tip to grid
    Hi 34K
    Lo 68K
    Tip to sleeve
    Hi 1M
    Lo 136K
     
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  12. Tom Kamphuys

    Tom Kamphuys Tele-Holic

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    Your tube side measurement seem ok. I suspect the input (wiring and/or type).

    Check the link for detailed wiring examples. I should have checked it also as my info (and a whole lot more) is also on that page...
     
  13. Doctor49

    Doctor49 TDPRI Member

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    Thanks for the replies. Much appreciated.
    Useful to know about the pdf issue, I will post in alternative form soon.
    I will also get the visual done when I get the time.
     
  14. dan40

    dan40 Tele-Afflicted

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  15. Doctor49

    Doctor49 TDPRI Member

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    Yes, I did thanks.
     
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  16. King Fan

    King Fan Poster Extraordinaire

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    BTW, if it doesn't turn out to be input related (here's hoping that's all it is), and along with a renewed voltage table, I bet the eagle-eyes here could use close-ups of your pot and socket wiring.

    You mentioned gear to follow the signal path. I don't know the 'best' DIY audio tracer, but Billm made a nice simple one in this video. There are lots of other simple ways.

    *But* for 'too clean' you may want to trace *voltages.* Luckily Fender shows AC test points on the 57 Deluxe schematic. See 'note 6': I think they test with all pots at 50% and with a 100mVAC test signal. For a signal generator, I found a free app for my phone and adapted an old stereo mini-jack spliced (mono) onto an old guitar cable. If your phone is all Lightning / USB-C there are also computer apps that'll work.
     
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  17. Doctor49

    Doctor49 TDPRI Member

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    Thanks for this and the Maintenance Manual link.
    I'm working through this week as Thailand doesn't "do Christmas" so I'll pick up at the weekend and post photos and a more accessible voltage record.
     
  18. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Can you post the transformer model numbers to be sure they are correct?
     
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  19. D'tar

    D'tar Friend of Leo's

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    Your PT should have accommodations for 230 vac.
    Screenshot_20191224-225627_Chrome.jpg

    +1 recommending trace voltage AC through the circuit with a signal generator.

    Also would like to see close up of the input/output jacks, control pots and tube sockets.

    FWIW... If these loose ends are still hanging around, they need tidied up with some shrink tube.

    20191224_230306.jpg



    A couple pictures of the monorail would be cool tooo!:)
     
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  20. D'tar

    D'tar Friend of Leo's

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    Does your mute switch have a shielded cable? I cant see the shield being grounded. If there is one make sure it is grounded only one end and no stray wires shorting between connections.
     
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