5f1 build volume/distortion issue

Discussion in 'Shock Brother's DIY Amps' started by jlang, Apr 1, 2019.

  1. jlang

    jlang TDPRI Member

    Age:
    45
    Posts:
    15
    Joined:
    Sep 4, 2018
    Location:
    Edmond, OK
    Hey all,
    I need some help. I recently replaced a preamp socket and did a few reflows to fix some cold soldering issues. Now when I power it up and plug my guitar in I have about 1/2-3/4 the power I did before the changes. It really only gets to decent volume when I turn it up to 12. I also get a lot more distortion than before, especially when I hit the higher strings.

    Some notes:
    I accidentally turned the amp on, about 1-1.5 minutes, without the speaker plugged in at one point.


    The amp is dead quiet, no weird noises coming out of it. No weird smells, etc. The tubes seem to be fine but I've only kept it on a little at a time to test and take voltage readings.

    I'm also getting a few weird readings:
    My PT is a classic tone 40-18019
    My OT is a classic tone 15 watt 40-18031

    5Y3 Rectifier pins 2 and 8 (yellow): 880 AC
    5Y3 Rectifier pins 4 and 6 (red): 340 AC

    Heater Voltage: 3.1


    Everything below is DC:

    B+1 Measured at the first filter cap: 399

    B+2 Measured at the second filter cap: 335

    B+3 Measured at the third filter cap: 269



    The 6V6's cathode (pin 8): 21 DC

    The 12AY7's plates (pins 1 and 6): (1)132, (6)134

    - Its cathode: 2.0
     
    Last edited: Apr 1, 2019
  2. dan40

    dan40 Tele-Afflicted

    Posts:
    1,381
    Joined:
    Aug 19, 2015
    Location:
    Richmond Va
    Your DC voltages don't look to crazy. If the amp is now playing at lower volume than before, I would check all of the new solder joints that you made when replacing the socket. Chances are you may still have a bad joint that is causing the lower output. Can you post clear pics of the amp's interior?
     
  3. jlang

    jlang TDPRI Member

    Age:
    45
    Posts:
    15
    Joined:
    Sep 4, 2018
    Location:
    Edmond, OK
    AC2B0A17-065B-4E18-A0FB-4A49E20C8EE4.jpeg 03A13E60-93E9-43C9-BA69-6B7D1A8E40FD.jpeg 335F2E8E-8B53-4567-973A-6B6B041FE530.jpeg A01E011E-D4EB-408B-99B9-DFABE470D47D.jpeg DF1D12CE-5AAC-4391-BA66-912317F3C122.jpeg 1827DB2B-C437-4249-AC7B-58F0BF4B9398.jpeg F8D7146B-6221-4E54-AA66-389F6E41F84F.jpeg It’s ugly. And I pulled a couple of wire that were underneath the board and put them on top. Could it be an overheated volume pot?
     
  4. intensely calm

    intensely calm Tele-Meister

    Posts:
    121
    Joined:
    Apr 1, 2019
    Location:
    Florida
    Have you made headway correcting this issue?

    If so, what did you find?
     
  5. Linkjr

    Linkjr Tele-Meister

    Age:
    49
    Posts:
    114
    Joined:
    Aug 16, 2017
    Location:
    Uk
    Did you try changing tubes? Check the ground connections are solid
     
  6. D'tar

    D'tar Friend of Leo's

    Posts:
    2,286
    Joined:
    Jan 11, 2013
    Location:
    WNY
    Can you confirm v1b cathode resistor... To me it looks black green red. Should be brown green red.

    Both cathodes 2.0vdc?
     
  7. intensely calm

    intensely calm Tele-Meister

    Posts:
    121
    Joined:
    Apr 1, 2019
    Location:
    Florida
    Looking at the photos, I don't see any insulator material between the chassis and the turret board. Is there any insulator there?

    The blue SoZo V1A 0.022uf Coupling Cap looks a little toasty, maybe this happened during assembly rather than use.

    My next question needs someone with 5F1 experience to weigh in.
    The 22K Negative Feedback resistor appears to be a 2watt variety in the photo, and the 22K resister between B2 and B3 filters looks like a 1/2watt. Shouldn't the cap at the filters be a 2watt rather than the NFB?

    My guess is these two resistors may be switched, but I would like to hear from 5F1 builders on this.

    1.jpg
     
    King Fan, Paul-T and D'tar like this.
  8. Linkjr

    Linkjr Tele-Meister

    Age:
    49
    Posts:
    114
    Joined:
    Aug 16, 2017
    Location:
    Uk
    Yes my 5f1 schem shows the 2watt between the filter caps not in the neg feedback, I would also def swap out that coupling cap but woul swap the resisters around first (and check the value of the 1/2watt with multimeter)
     
  9. Paul-T

    Paul-T Tele-Meister

    Posts:
    242
    Joined:
    Nov 23, 2018
    Location:
    London
    I agree. I don't know enough about those coupling capacitors to say for sure but they look in poor shape.

    I think if you're working on the board, swapping the 22k resistors around, you should reorientate the 470 Ohm 2W as it looks to be sitting right next to the 22/25 ohm cathode bypass. That resistor gets pretty hot, too.
     
  10. King Fan

    King Fan Friend of Leo's

    Posts:
    4,219
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    It looks like the last time we heard from the OP was 4/1...


    Sent from my iPad using Tapatalk
     
    Paul-T likes this.
  11. allesz

    allesz Tele-Meister

    Posts:
    461
    Joined:
    Sep 13, 2010
    Location:
    Italy - Bologna
    Hallo, maybe I'm late, but check the heater wiring: 3,1 Volts are too low.
     
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.