All is not right with my new 5E3 build...

Discussion in 'Shock Brother's DIY Amps' started by dunehunter, Jul 21, 2019.

  1. dunehunter

    dunehunter Tele-Holic Double Platinum Supporter

    Age:
    65
    Posts:
    579
    Joined:
    Jul 14, 2011
    Location:
    Larkspur, CO
    So when I finally got the opportunity to really crank it (wife out of house), the "normal" channel of my new 5E3 worked just fine. But when I plugged into No. 1, bright channel and cranked it up, loud squeal. Subsequently, on playing around with it, I also was getting a tremolo like sound--start, stop, start, stop.

    I've re-flowed the solder on the connections at the jacks and all appears to be okay. Also re-flowed the solder at the grid stoppers. I'm getting good 1M resistance on a 1/4" plug in the Bright jack.

    I've also replaced the 12AY7 in V1 and same result.

    Upon playing with it a little more, I noticed the squeal and tremolo effect goes away when the tone pot is at zero.

    Could a bad tone pot be causing my problem? Any other thoughts?
     
  2. Dacious

    Dacious Poster Extraordinaire

    Posts:
    6,744
    Joined:
    Mar 16, 2003
    Location:
    Godzone
    It sounds like an oscillation problem. Try swapping the two plate leads as a quick and dirty. You have no NFB so that should not impact. Did you try swapping the second preamp tube? The other thing is your power tubes. One might have a loose element. Without hearing a sample it's hard to say.

    These don't have a 'bright' input. One input on each channel is high impedance and one low. The high impedance with guitar pickups will generate more input gain and therefore more output volume.
     
    Paul G. and dunehunter like this.
  3. King Fan

    King Fan Friend of Leo's Ad Free Member

    Posts:
    3,847
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Does this amp have mods? It might help sharp-eyed folks here to see some pics, with close-ups of the input and tone sectors, as well as a voltage table.
     
    dunehunter likes this.
  4. dunehunter

    dunehunter Tele-Holic Double Platinum Supporter

    Age:
    65
    Posts:
    579
    Joined:
    Jul 14, 2011
    Location:
    Larkspur, CO
    oops
     
  5. Nickfl

    Nickfl Tele-Afflicted

    Posts:
    1,539
    Joined:
    May 24, 2016
    Location:
    Florida
    I agree that it sounds like it is oscillating. Check your lead dress and tap the tubes gently with a chopstick to see if any are microphonic.
    I would think it would take some pretty serious lead dress mistakes to cause such a simple amp to oscillate the way you're describing but it's certainly a possibility and pictures would help. Alternatively a bad coupling cap can supposedly cause these motorboating symptoms so if the lead dress is okay and none of the tubes are microphonic that might be something to consider.
     
    D'tar and dunehunter like this.
  6. sds1

    sds1 Tele-Afflicted

    Age:
    42
    Posts:
    1,060
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    The tremolo sound -- consider that it's perhaps a computer router, modem, or other piece of electronics in the vicinity. I hear this all the time -- a tick tick tick tick. Maybe 2-3 ticks per second. Starts and stops randomly.

    Your tone pot is probably a red herring -- turning it down is reduction in gain. The feedback loop (oscillation) is a product of gain. Therefore any gain controls in the feedback loop are expected to have a direct effect on the oscillation.
     
    tubedood and dunehunter like this.
  7. dunehunter

    dunehunter Tele-Holic Double Platinum Supporter

    Age:
    65
    Posts:
    579
    Joined:
    Jul 14, 2011
    Location:
    Larkspur, CO
    Pictures coming soon. And voltages. Just waking up. Need coffee.
     
  8. dunehunter

    dunehunter Tele-Holic Double Platinum Supporter

    Age:
    65
    Posts:
    579
    Joined:
    Jul 14, 2011
    Location:
    Larkspur, CO
    Here are pictures. A couple of notes: 1) This amp has one mod--the master volume in the lower right corner in No.2 input slot of the "Normal" channel. 2) I rebuilt the tone/volume section although, as @sds1 notes, this could be a red herring. 3) As I tore it apart last night, will need to redo the voltage chart.

    5E3 Back.jpg
    5E3 Top.jpg
    5E3 Bottom.jpg
    Also, I really STILL do not understand the concept of "lead dress".
     
  9. RollingBender

    RollingBender Tele-Holic Vendor Member

    Posts:
    990
    Joined:
    May 14, 2011
    Location:
    SW Minnesota
    Cell phone close to the amp will make strange noises too. My first build was making an odd noise. I decided to google the symptom and picked up my cell phone from the top of the amp and the noise went away.
     
    jtcnj, danlad, sds1 and 1 other person like this.
  10. King Fan

    King Fan Friend of Leo's Ad Free Member

    Posts:
    3,847
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Lots of details with the devil in 'em, but here’s what lead dress "looks like" from a great recent build by @Phrygian77 — the leads lie down against chassis; if they meet at all they meet at right angles, especially where the Southern cross the Yellow Dog... er, I mean where signal crosses voltage; parallel leads, especially with equal voltages, or high voltage, are tightly twisted, and so on.

    [​IMG]




    Sent from my iPad using Tapatalk
     
    Phrygian77 and sds1 like this.
  11. dunehunter

    dunehunter Tele-Holic Double Platinum Supporter

    Age:
    65
    Posts:
    579
    Joined:
    Jul 14, 2011
    Location:
    Larkspur, CO
    My radio-controlled lighting in my workshop causes fairly loud hum. When I remove the amps to my play room, the hum goes away. Similar phenomenon, I guess. But, no, cellphone has never caused any issues for me.
     
    sds1 likes this.
  12. dunehunter

    dunehunter Tele-Holic Double Platinum Supporter

    Age:
    65
    Posts:
    579
    Joined:
    Jul 14, 2011
    Location:
    Larkspur, CO
    Wow! Thanks for that. Geez, that's nice work...
     
    Phrygian77 likes this.
  13. dunehunter

    dunehunter Tele-Holic Double Platinum Supporter

    Age:
    65
    Posts:
    579
    Joined:
    Jul 14, 2011
    Location:
    Larkspur, CO
    The really exasperating part is that it seemed to all be working when I first fired it up. And I was sure I'd tested all the inputs, too. Think I'll fire it up and chopstick it like @Nickfl has suggested.
     
  14. D'tar

    D'tar Friend of Leo's

    Posts:
    2,128
    Joined:
    Jan 11, 2013
    Location:
    WNY
    IMO. a stock 5e3 lead dress is pretty forgiving. Meaning, I've seen some pretty wild wiring which the owner claims to be super quiet. The area below would be worth chopsticking. The yellow wire could be dressed downward as suggested by the dotted line. tucking wires close to the chassis helps shield from interference . I would also try moving the red wire around. You are right on top of of your plate B+. try moving the whole MV wiring around. Maybe even remove the pot from the chassis temporarily.

    bright caps are easily overheated and may cause squeal.

    A bad power tube can cause oscillation.


    upload_2019-7-22_9-33-47.png
     
    dunehunter and King Fan like this.
  15. Snfoilhat

    Snfoilhat Tele-Afflicted

    Age:
    38
    Posts:
    1,085
    Joined:
    Apr 8, 2016
    Location:
    Oakland, CA
    Without knowing more, my first guess would be the MV. You are piping signal from late in the amplifier back into the vicinity of the earliest stage of the amplifier. I use shielded cable for this type of long, across-the-chassis lead.

    Also, what's up w/ the black wire at the intersection of the PI's cathode and tail resistor? I'm looking at Robrob's 5E3 layout, and I don't see anything inserting there. Is that somehow hooked into your MV, like its signal ground? That may not be the best spot, raised above ground potential by the tail resistor.

    Apologies if I'm seeing it wrong

    Edit: now I see -- the grid leak resistor is missing too. It's that type of prePIMV. Anyhow, you may find something in the first bit of my post. Cheers
     
    sds1, dunehunter, King Fan and 2 others like this.
  16. D'tar

    D'tar Friend of Leo's

    Posts:
    2,128
    Joined:
    Jan 11, 2013
    Location:
    WNY
    that is the MV mod

    [​IMG]
     
    King Fan and Snfoilhat like this.
  17. dunehunter

    dunehunter Tele-Holic Double Platinum Supporter

    Age:
    65
    Posts:
    579
    Joined:
    Jul 14, 2011
    Location:
    Larkspur, CO
    I've wondered about this...
     
  18. Phrygian77

    Phrygian77 Tele-Afflicted

    Posts:
    1,698
    Joined:
    Apr 30, 2016
    Location:
    Crawfordville, FL
    Thanks for the complement! I've pretty much copied pre-CBS Fender lead dress, incorporating a few of my own changes and ideas. It works really well, so no reason to reinvent the wheel.

    I know a lot of people don't like the solid vintage cloth wire, but it stays put, and also reduces the possibility of vibration in the wiring causing problems.
     
    20strings likes this.
  19. Teleguy61

    Teleguy61 Friend of Leo's

    Posts:
    2,726
    Joined:
    May 17, 2010
    Location:
    Eastern Massachusetts

    Shielded cable for areas with widely differing signal levels are a good idea.
    Remember to only ground the shield at one of the run, typically the higher level end.
    If you connect the shield at both ends of the run, you risk formation of a ground loop, which will bring its own noise issues.
     
    dunehunter likes this.
  20. sds1

    sds1 Tele-Afflicted

    Age:
    42
    Posts:
    1,060
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    That MV signal wire is prime suspect. Shield it and my money says problem solved.

    That master volume signal wire will couple in-air with an in-phase signal in the Preamp, this is a positive feedback loop and with enough gain it is guaranteed to oscillate. Same as when you get your guitar too close to the speaker - - with enough gain it will feed back every single time.

    Shielding it prevents the in-air coupling, now there is no feedback loop.

    If you could somehow route the MV wire to avoid all in-phase signal in the preamp, the positive feedback loop is eliminated as well. But that's harder to do. Use the shielded cable, it's a slam dunk.
     
    dunehunter likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.