5F1 no sound

Discussion in 'Amp Tech Center' started by scottc311, Sep 30, 2019.

  1. scottc311

    scottc311 TDPRI Member

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    Hello, I just bought and wired a 5f1 kit from mojotone and it lights up and all but i’m not getting any sound, i have taken some photos in hopes some of you may be able to help please and thank you!
     

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  2. BigDaddy23

    BigDaddy23 Tele-Meister

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    Have you got a wire taking power from the 3rd filter cap to the junction of the 2 plate resistors for V1? I can't see one above the board but it may be underneath. That would be a culprit if you are getting no amplification. See red line in the pic. If you have a multimeter, check if you have continuity between those 2 points. If you don't, add a wire there! Just another thing I noted is that your blue heater wires aren't twisted - consider redoing them as a twisted pair to limit hum.

    5f1.jpeg
     
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  3. dan40

    dan40 Tele-Afflicted

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    I mentioned in your other post but check the cathode connection on the 6v6 socket. It looks like the cathode wire goes to pin 1 instead of pin 8. It needs to be on pin 8 to function properly.
     
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  4. scottc311

    scottc311 TDPRI Member

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    Hey thanks for the advice i will twist up the wires, and i have a wire connecting them i have to get a better multimeter to check for continuity
     
  5. scottc311

    scottc311 TDPRI Member

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    Hey thank you! I’m going to check it out right now
     
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  6. Wally

    Wally Telefied Ad Free Member

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    What are your voltages? Make a chart. Do you have ‘white noise’ from the speaker?
    Just an observation, but your are cutting the cloth back too far and have bare conductors close to ground points.
     
  7. Wally

    Wally Telefied Ad Free Member

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    A voltage chart or at least a full circuit voltage check, which should be made as soon as the amp is fired up imho, would reveal such an error immediately.
     
  8. scottc311

    scottc311 TDPRI Member

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    Hey there! I just checked and i do have contiunity between both points!
     
  9. Wally

    Wally Telefied Ad Free Member

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    And the voltages????? Note: It takes a while before I give up.
     
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  10. BigDaddy23

    BigDaddy23 Tele-Meister

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    Haha!

    @scottc311 - You need to go through and verify all your connections and component values are correct.........and take voltage measurements!
     
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  11. Wally

    Wally Telefied Ad Free Member

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    And...the voltage measurements might reveal connection issues. The circuit is there so the current can travel from point to point. If it doesn’t travel to a certain point, it’s absence is immediately noticeable. One can listen to the lack of sound and visually inspect thingss, but a meter gets to the point quickly and without question.
     
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  12. scottc311

    scottc311 TDPRI Member

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    Ok, what connections should i check? And is it ac or dc?
     
  13. Wally

    Wally Telefied Ad Free Member

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    There is a good question. The high tension secondary feeding the rectifier pins 4 & 6 will be AC. You can read each leg to ground and/or from pin to pin. The leg to ground will be half of the pin to pin. Rectifier heater voltage will be in AC. From ground to pin 8 you will read in DC. This is the B+ to one end of the OT primary winding. You could check each node of the power supply.....or you could go directly to measuring the plate and cathode voltages....all to ground. When you check the power tube plate, you should hear a pop through the speaker. If not, there is a problem there. The plate on the driver triode should be a louder pop. If not there, is a problem. The plate of the preamp triode should be the loudest pop. Make a chart for each tube’s pins and record the voltages....or list the pins for each tube with the voltage for each. The heater voltages will be AC. If you don’t know the tube pinouts, go here...Duncan Tube Data Sheets..... for that info. I find that drawing these pinouts out for yourself helps to imbed the info.
    Example chart...
    V1 12AX7
    P1— voltage
    P2—
    And so on.

    V2 6V6

    V3 5Y3

    Caution...live circuit with dangerous voltages. Imho, one should know how to read voltages in an amp before building one...but it is never too late to learn.
     
  14. peteb

    peteb Friend of Leo's

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    On the 6V6, first check the DC voltage on pins 3, 8, then 4 if necessary, the plate, the cathode and the screen. Measure these to ground.

    Then check the AC voltage on pins 2 and 7, the heaters.


    There should be around 400 volts on the plate and screen and around 20 volts on the cathode.



    The heaters should measure about 3 volts to ground or around 6 volts between them.



    If the problem doesn’t show up, check pin 5, the grid. There should be very little to no AC or DC there.



    Good advice Wally. Not trying to add anything, we must have been typing at the same time, but you posted while I was putting the chicken in the fridge
     
    Last edited: Oct 1, 2019
  15. scottc311

    scottc311 TDPRI Member

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    I had to return the multimeter i was borrowing and i’m getting one tommrow but this is what i have so far

    6v6
    P1
    P2 3ac
    P3 352dc
    P4 332dc
    P5 20dc
    P6 none
    P7 3 ac
    P8 236dc

    I will post the rest tommrow after i get the meter, thank you all for your help so far!
     
  16. Wally

    Wally Telefied Ad Free Member

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    The voltage on pin 8, which is the cathode, should be around 20vdc, ime. Also, you should not be reading a voltage on pin 5, the control grid.

    Can you post the layout and a schematic that came with the kit, please?
     
  17. scottc311

    scottc311 TDPRI Member

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  18. scottc311

    scottc311 TDPRI Member

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    Also i found a multimeter,

    12Ax7
    P1 188dc
    P2 236 dc
    P3 1.55 dc
    P4 04ac
    P5 03ac
    P6 291dc
    P7 100 dc
    P8 218 dc
    P9 3 ac
     
  19. Wally

    Wally Telefied Ad Free Member

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    You should not have 236vdc on the pin 2, which is the input control grid. You don’t have heater voltage at pins 4/5....it should be equal to that voltage on pin 9. Pin 7 voltage is incorrect as is pin 8 as I noted above. You have some errors in your wiring. That circuit is hard to see because of the shape of the chassis.....tweeds demand a close look at certain angles to make things understandable.
    Hopefully, you know how to drain the caps so that you can safely do some searching to ascertain where the errors are. The layout, a meter and your eyes are all you have. This is when the learning begins, I suppose. One has to clear the mind, admit that errors were made, and have an open mind to that so that the search for the problems will be fruitful. Good luck.
     
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  20. peteb

    peteb Friend of Leo's

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    I agree with what Wally said



    P1,,p2,p3 are the plate, grid and cathode of v1.

    The plate is good, the grid is not and the cathode is. The cathode voltage indicates this tube is drawing current as it should.


    P4 and p5 are the heaters. Should be more like 6-7v.


    P6, p7,p8 are the plate, grid, cathode of v2. The plate is good, the grid and cathode are way off.



    The fact that the plates have the right high voltage DC on them shows the DC power supply is working.


    EDIT: as it’s wired, shown in post 17, all of the heater voltages on both the 6V6 and 12 AX7 should measure about 3v to ground.
     
    Last edited: Oct 3, 2019
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