5e3 Hum with instrument only

Discussion in 'Shock Brother's DIY Amps' started by Steve77, Jan 26, 2020.

  1. Steve77

    Steve77 TDPRI Member

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    81543810-703B-410D-960C-D76A61D00E6F.jpeg DF498436-7153-4C41-A4DF-435FC9C3A22E.jpeg 4DA7DC2C-6837-4A0F-8393-F364BB31B437.jpeg B4BA3EBF-5CAF-44D8-9ED9-631A5B54446B.jpeg 5DC80824-B317-4B2B-AE1B-6AB4C8AC9193.jpeg C6876504-7BEC-4BC2-944C-9A3E11F55AB5.jpeg Ok I’ve tried digging around and only found a few threads that were close but no cigar.
    Yup another amp hum thread.
    I’m close at this point but here’s my problem.
    Amp on and nothing plugged in it’s quite. I can turn volumes or tone full and only getting the expected light hiss.
    If I plug an instrument in and turn the volume up I get hum. It increases with volume and changes “pitch” when the tone is increased. Guessing something around the inputs.
    Before anyone asks, I have tried numerous guitars. From single coils to humbuckers even emgs. Numerous cables and even tried different locations. If ignore the hum it sounds amazing.
    This is not a new build. It started life a handful of years ago as a Mojotone build. Since then it has gone through numerous mods, back to stock then modded again, ect ect. It has always had hum to some degree.
    Currently it has a classic-tone 40-18078 PT using the 355v. I have a NOS 5y3. My voltages are sitting at then levels everyone posts as normal. The volumes/tone have been changed to the 6g3 layout. I know it’s not a true 5e3, but currently suits my needs. I’m sure at some point it’ll go back to stock again. The tubes are all new. And I had tried my back up sets with no change. I just rewired the filament heaters. Changed out filter caps. And corrected a few ground connections. The grounding is the same as on Robrobinettes 5e3 page. The center tap is elevated.
    This all got rid of a slight bit of hum that was happening all the time. I will of course go back over wiring and solder joints again and again.
    A few more eyes and a ton more experience would be greatly appreciated.
    I can supply more pics if needed of course.
     
  2. BobSmith

    BobSmith Tele-Meister

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    Amp working fine, then not working...so it was wired fine. That’s an important clue.

    I would get a good inspection light and magnifying glass and inspect all components and joints. Reflow or replace anything suspicious. You don’t need a schematic even. That’s not your problem here.

    This could be challenging as there are many damaged wires in there already. The ones going to the rectifier look particularly bad (and possibly dangerous). Really any damaged wire should be replaced (if insulation is damaged if will no longer carry the rated specifications).

    Order some Chinese food tonight and put the chopstick to good use here. A cheap glue brush could be helpful too (I found a small piece of stranded wire once shorting a connection.). Brush everything as you go along.

    If you could borrow a signal generator and scope you could trace the signal thru the circuit.

    I inherited something pretty similar few months ago. Total mess (but worked). I took a bunch of pictures, then completely took it apart. I’m talking every component came off the board. Cleaned everything up then replaced all the wires. It took some time but was worth it in the end. Something will break in time and it’s easier to find later if you go thru this pain.
     
    Last edited: Jan 27, 2020
  3. Steve77

    Steve77 TDPRI Member

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    Sigh,
    As soon as I started taking pictures I realized I was a bit embarrassed by what it had become. I hadn’t even noticed the burn through on the rectifier wire. Loved to pretend this was a hand me down, but sadly it is one of my early diys. Over modded. I have learned way more since and can do better.
    A redo it is. I think I’ve been avoiding it.
    It wasn’t perfect working then not. This thing has hummed since the beginning, though I seem to have gotten rid of one hum in exchange for more of another. I’ve lived with hum as the guitar tone was too awesome. My jam mates were probably sick of it!
    I did chop stick it. Sorry forgot to add that. The only thing I notice was that it hummed when the chop stick got into the input jack area.
    Going to get rid of all the vintage style cloth style wire. Is there a gauge you guys would recommend? Solid core I would assume? Or should some be strand?
     
  4. Paul G.

    Paul G. Friend of Leo's

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    The type of wire or insulation makes no difference.

    Just for S&G try to shield your back panel. Try running shielded cable from the input jacks to the grids of V1, with the grid stopper resistors at the tube end. Connect the shield to ground only at one end (usually at the jack because it's easier).
     
  5. Steve77

    Steve77 TDPRI Member

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    Read a few things about shielding the inputs. I have some left over from a les paul rewire and will added it in for sure.
    Did a search and saw the same, Type didn’t really matter. Read that 22awg would work as it would fit the tube sockets. And use 20awg on the filament wires.
    Sorry not sure what you meant by S&G.
    Did you mean adding the foil to the wooden back panel? Same as shielding guitar cavities. Makes sense.
     
  6. Preacher

    Preacher Friend of Leo's

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    S&G

    poops and giggles? PG rated lol.

    So I had a similar build. First timer, soldered everything up pretty badly I must say. I still had hum so I took the board out even though I was not wanting to redo it, re-flowed everything and cleaned it up as best as I could. I then ran some new wires where my old ones showed laser burns from being too close to the iron. I was amazed as how much I learned from the time I first wired up the amp to the second time. My hand was more steady, I had dialed in my iron where it was a quick touch and viola a good shiny solder joint, and my wiring did not look like it had been in an episode of Star Wars.

    When I cut it on after that I had some jack issues and found I had created a ground look with a grounded jack and a ground wire. Fixed that issue and it was quiet.

    Bite the bullet, take it apart and rewire it, you will thank yourself later.
     
  7. Lowerleftcoast

    Lowerleftcoast Tele-Meister

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    The 1meg on the input jacks can cause trouble. Position them laying close to chassis.

    Go over the input circuit. The 5e3 is old school. You can benefit from better routing and shielding.
     
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  8. King Fan

    King Fan Friend of Leo's

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    One easy check around input jacks: Have you tested resistances with a plugged-in cable (or better yet a naked jack)?

    upload_2020-1-27_10-48-48.png

    An easy test for heater hum is to lift the 6.3V wiring to the tubes off the lamp and run the heaters on a 6V battery...
     
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  9. Steve77

    Steve77 TDPRI Member

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    Thanks for all the help/tips. Heading to the local electronics store tomorrow to get fresh wire and maybe a new soldering iron. Old ones, well, old. Going to take all the advise and use it in a redo. I’ll post back, hopefully with a super quite, awesome sounding, clean rebuild!
    king fan, never heard of testing the inputs, I’ll give that a try too for sure.
     
  10. clintj

    clintj Friend of Leo's

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    You're not testing it with the back off under a fluorescent work light by chance, are you?

    Sent from my Pixel 2 using Tapatalk
     
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  11. Steve77

    Steve77 TDPRI Member

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    No, I suspected the same. I moved it around the house. Made sure I used different outlets and different locations.
     
  12. Steve77

    Steve77 TDPRI Member

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    Ive actually already torn it apart. A few wires under the board had dodgy solder joints. My technique years ago sucked. I’ve done a bunch of reading over the last few days. I was not attaching wires mechanically, then Soldering. Thinking there were probably a bunch of questionable connections.
    A total redo will hopefully solve my issues.
     
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  13. TobyZ28

    TobyZ28 Tele-Meister

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    I noticed from the pic the lower input jacks are very close to the board, they may be making contact (or are VERY close to making contact) when the jack is in. Something to look out for when you put her back together, good luck!
     
  14. Steve77

    Steve77 TDPRI Member

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    Hmm thanks Toby, I’m actually redoing the inputs now. Just to be safe I’ll reorient them.
     
  15. schmee

    schmee Poster Extraordinaire Silver Supporter

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    I cant tell from the pics much, but I found building a 5E3 that the preamp and input jack grounds must be located near the input jacks, and the power section grounds must be near the power tranny. In other words separated. It surprised me how much it mattered.
     
  16. Steve77

    Steve77 TDPRI Member

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    fresh separated ground installed and even reoriented to input jacks.
    Question though.
    I had enough 600v rated wire to do everything except the long heater run.
    I can only seem to get automotive wire in town here. I know it can’t be used anywhere else as it’s rated to 60v but could it be used safely for the heater wire as it’s only 6.3v?
     
  17. jimgchord

    jimgchord Tele-Afflicted

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    Redo the inputs with rg174 cable, solder the shield only at the jack end.
     
  18. Steve77

    Steve77 TDPRI Member

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    Just to make sure I use the right cable.
    Rg174 is essentially tv coax cable?
     
  19. Steve77

    Steve77 TDPRI Member

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    Ok actually found the answer for my self. Rg6 is tv coax. Rg174 is more the modem type. Is there a big difference between the two? Rg174 seems a bit tough to find in my area.
     
  20. Steve77

    Steve77 TDPRI Member

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    Sigh, again I should search first then ask. Rg174 is significantly smaller. Got it. I’ll just amazon it and get it done.
     
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