5E3 Deluxe Micro - Troubleshooting

Discussion in 'Shock Brother's DIY Amps' started by Autriche, Sep 26, 2019.

  1. Autriche

    Autriche TDPRI Member

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    Hey everyone :),

    For my first amp build I wanted to build @robrob 's micro deluxe.

    I decided to go with:
    - solid state rectifier
    - Hammond 269EX 190V-0-190V PT (I used the black 125V and not the grey 115V wire)
    As per Robs recommendation, I replaced the B+2 27K ohm 2 watt voltage dropping resistor with a 22K.

    I followed Rob's amp startup procedure and nothing exploded (I did wear safety goggles). The amp works but the maximum volume is quite low (Weber 12A125A).

    However, I seem to have some issues:

    1. The measured voltages for B+1, B+2 as well as the plates seem low:

    PT out 208 & 207 (415 across)
    Heaters 6.9V
    B+1 266
    B+2 222
    V1A pin1 109
    V1A pin3 1.6
    V1B pin6 112
    V1B pin8 1.6
    V2 pin1/6 250
    V2 pin3/8 9.8


    2. I have a fairly loud hum that:
    - fairly certain its 60 cycle hum
    - is not affected by plugging in a guitar cable
    - as far as I can tell unchanged when I move wires around
    - However, the hum volume is dependent on the master volume (but the vol pot changes it sightly as well)

    I dont have spare tubes to test but a bad preamp tube could be the problem.

    Any idea what I could/should do about the hum & low voltages? I'd appreaciate any suggestions!
    IMG_0092.jpg
     

    Attached Files:

  2. Edvin

    Edvin TDPRI Member

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    U could try 2 x 100ohm resistors from filament to ground for artificial centertap.
     
  3. D'tar

    D'tar Friend of Leo's

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    Does the 1st node have a ground/chassis connection?

    And yes as edvin states. That pt needs an artificial heater center tap.
     
  4. Autriche

    Autriche TDPRI Member

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    Thanks!
    Silly mistake. Adding the artificial center tap solved all the hum problems! :)

    I noticed today that the bass is farting out when I turn the amp up. The speaker is sitting on the bench right now which may be the issue.
     
    Last edited: Sep 27, 2019
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  5. dan40

    dan40 Tele-Afflicted

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    5e3's are a bit farty by nature when turned up. Being a micro amp with small transformers will only make this worse. There are some circuit tweaks that folks do to the 5e3 to help tighten it up but you want to make sure that your build is working 100% correctly before attempting any mods.
     
  6. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Autrichie, have you played through a full size 5E3 amp? If not, your amp may be acting normally.

    You can try a larger first filter cap size by temporarily alligator clipping in another first filter cap in parallel to see if that helps.

    If you're sure the amp is running right you can clean up the 5E3 circuit by cutting the first 0.1uF coupling cap to .047 or .022uF.
     
  7. Autriche

    Autriche TDPRI Member

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    Hey Rob, thanks for the amazing info for this amp!
    I clipped a .047 cap across the first .1 but that didnt help.

    Other that the weird bass, the amp sounds fantastic.

    This is the sound I hear:

     
  8. robrob

    robrob Poster Extraordinaire Ad Free Member

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    That's not "farting out". That's some type of bass distortion. Try chopsticking the wire leads around and if you have them, try another set of tubes.

    Paralleling the .047 and .1uF coupling caps will give you .147uF and actually add bass response. Don't bother with this until we fix the distortion.

    I was suggesting paralleling another cap on the first big filter cap but if you used a 47uF like I show on the layout then that's plenty so you don't need to add more.
     
  9. Autriche

    Autriche TDPRI Member

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    Yeah, I used a 47uF for the filter cap.
    I will chopstick around for a bit and report back if that helped. I dont have a spare 12AU7 but I'll try to source a Tung-Sol and give that a shot.
     
  10. Asmith

    Asmith Friend of Leo's

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    Is it possible its an issue because the speaker isnt mounted to anything and is just rattling around on its backside.
     
  11. Autriche

    Autriche TDPRI Member

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    That probably doesn't help but that wasnt the problem. I received a new Tung-Sol 12AU7 today and that fixed my weird bass distortion problem :D

    It looks like the amp is working properly now. Again, thanks for the help!

    Now its time to tackle the cab. I'll keep you posted on that
     
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  12. Autriche

    Autriche TDPRI Member

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    1E333B2A-CEFD-4799-8A5E-F125682C3D5A.jpeg 057992C1-CFF0-4AEB-B673-8056299D6C47.jpeg D1C50A31-9C55-4EF0-9A68-4C3353CEFE86.jpeg 7F215EE9-2DBC-464C-AF29-1375355819BD.jpeg D8D40B66-9D12-40D1-B509-BEF10EFD8E7C.jpeg C94CCF9C-39A7-4161-8AA4-03A920B8DB82.jpeg 060E8A2B-5EC8-4F37-A38D-C3641216FBD9.jpeg 9C96BEC1-AF46-4B8E-96EA-B3433D935F72.jpeg 1879496A-E196-441D-AE0A-9ED22E5592C9.jpeg I had a busy month and wasn’t able to get this done as fast as I though but I’m pretty much done with the cab.

    Plenty of little mistakes but most don’t show :D

    However, I’m my tone control seems to do nothing really. I’ll have to look into that this weekend.
     
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  13. symbiotic

    symbiotic TDPRI Member

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    I like the bevels you have incorporated in your cabinet design. Sharp, and uncommon. Well done!
     
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  14. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    Is that cabinet material (the boards) thicker than the usual 3/4”?
     
  15. BigDaddy23

    BigDaddy23 Tele-Meister

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    Love the cab design! Well done.
     
  16. Autriche

    Autriche TDPRI Member

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    thanks! I wanted do something slightly different than a standard 5e3 cab. I thought sharp edges are easier to cover in tweed compared to rounded but the inside corners on the front were actually quite annoying to cover.


    thanks! I thought I’d do something sl
    that’s standard 3/4 from Home Depot. The baffle is 1/4 5-ply
     
  17. dan40

    dan40 Tele-Afflicted

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    You should also try replacing the 12au7 with a 12bh7 sometimes. It adds a touch more volume and a slightly firmer feel to the low end.
     
  18. Autriche

    Autriche TDPRI Member

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    Thanks! I'll give that a try
     
    dan40 likes this.
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