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Rookie Build: Champ 5F1

Discussion in 'Shock Brother's DIY Amps' started by TeleSlug, Jul 15, 2020.

  1. King Fan

    King Fan Poster Extraordinaire

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    By all means follow up on the above. If all your voltages and your OT are good, you may have a fault in your signal chain. Have you tried the "D'tar input jack test?"

    FWIW most of the solder joints on those input jacks look a little too economical of solder ('dry'). :) You might reflow any joints that don't have a moderate shiny blob of solder obscuring the whole wire/lug contact, there and elsewhere.

    @D'tar is right of course about RCA speaker jacks and plugs -- a true weak link. To test that, I run alligator clips from the speaker wires inside the chassis to the speaker lugs as it sits on the bench. Test for continuity, too, of course. It also protects your amp as mentioned by @andrewRneumann to make sure your speaker is connected. Once the amp works, you can go back to the speaker jack/plug and put the speaker in a cab. (Also FWIW, there's no functional difference between speaker (+) and (–) *when using a single speaker.* But let's not dwell on that -- it's a source of massive misunderstanding.)

    If your input and output chains work right, you can read about the 'pop' test' (see this nice post by our smart friend @dan40 ). If you pass that and the amp still doesn't work, we can discuss an audio signal trace and voltage signal trace -- really pretty easy.

    Oh, and final question, is that an *incandescent* bulb in your limiter? Hard to tell in pics...
     
    Last edited: Oct 3, 2020
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  2. TeleSlug

    TeleSlug TDPRI Member Silver Supporter

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    I sincerely appreciate all this help. I searched old threads last night and it seems like this "no sound" problem is not uncommon. I think I've tracked down everything that was requested for debugging.

    Mojotone calls this a "NOS 771" OT. The yellow wire goes to the RCA tip. The blue primary wire goes to pin 3 of the power tube and the red primary goes to the circuit board connection with the rectifier tube.

    DC resistance of the OT secondary fluctuates between .7 and 1.0 ohm.

    Resistance between the RCA tip and sleeve reads at .2 ohm.

    rectifier

    pin 2 = 346V
    pin 4 = 3.5 mV
    pin 6 = 2.0 mV
    pin 8 = 348V

    power

    pin 1 = 19
    pin 2 = 0
    pin 3 = 336
    pin 4 = 304
    pin 5 = 44 mV
    pin 7 = 0
    pin 8 = 19

    preamp

    pin 1 = 179
    pin 2 = 1.0 mV
    pin 3 = 1.3
    pin 4 = 0.5 mV
    pin 5 = 0.1 mV
    pin 6 = 180
    pin 7 = 0.4 mV
    pin 8 = 1.2
    pin 9 = 0

    Nope, no sound at all from the speaker.
     
  3. D'tar

    D'tar Friend of Leo's

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    Good stuff!

    Id like to see the latest voltages in the same format as post #46

    While checking those #'s the pop test is your friend. Be sure to turn up the volume to hear V1. The 6v6 ime, may not produce a profound pop but rather a scratching noise. ANY sound through the speaker suggests the ouput wiring is correct. Zero sounds indicates the need to scrutinize the output section/speaker connections
     
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  4. D'tar

    D'tar Friend of Leo's

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    Ha, nice timing!
     
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  5. TeleSlug

    TeleSlug TDPRI Member Silver Supporter

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    Thank you for those links. I will follow up, especially @D'tar 's input jack test to address silent amp syndrome.

    And yes, it's a 150 watt incandescent bulb. While I was poking around to get the updated voltage readings it stayed at a dim glow.
     
  6. D'tar

    D'tar Friend of Leo's

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    This will make the sound of silence!
     
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  7. King Fan

    King Fan Poster Extraordinaire

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    LOL, yes.

    I consider myself decent at soldering, by now, but my batting average building RCA plugs is abysmal. In addition to alligator leads to bypass the jack, plug, and cable altogether, an easy test to confirm a plug issue is to sacrifice any old commercial RCA cable you have lying around for use as a speaker cable.
     
    Last edited: Oct 3, 2020
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  8. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I'll bet D'tar has found the source of silence with the speaker jack but here are some numbers that can cause silence as well.
    Pin 2 and 7 on the power tube should be metered as VAC but to have "0" VDC meter reading may indicate the tube is not be getting heater voltage. (I know you said all tubes light up but just make sure.)
    Pins 4 and 5 are connected together. They should read the same. Again the pin4/5 pin9 is the 6.3 heater and should be metered as VAC. Configured for a 6.3VAC heater, if only pin4 and pin9 were conducting only 1/2 of the 12a_7 would be heated which could lead to silence.

    Disclaimer: A meter will not give a repeatable measurement when the voltage is AC and the meter is set to DC. So, the above observations may come to naught.
     
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  9. D'tar

    D'tar Friend of Leo's

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    Im "assuming";)....

    That the meter was not switch to read vac as we have cathode voltages showing
     
    Last edited: Oct 3, 2020
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  10. TeleSlug

    TeleSlug TDPRI Member Silver Supporter

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    We (and I do mean we) have a working amp!

    I followed up on the links and advice from @King Fan. I reflowed the input jacks, redid the RCA jack, and did the pop test. Success.

    I plugged in, played an Em, and angels began singing.

    Thank you so, so much for all your help. I will post a video shortly.
     
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  11. andrewRneumann

    andrewRneumann Tele-Holic

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    That’s awesome. I’m happy for you! It’s a great feeling isn’t it?!
     
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  12. James Knox

    James Knox Tele-Holic Silver Supporter

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    Good job!
     
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  13. TeleSlug

    TeleSlug TDPRI Member Silver Supporter

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    Here is just a quick take with my Tele. At first, just a few open chords on the bridge pickup and then the Julian Lage piece I am slooooowly working on through the humbucker. Now that this project is complete I can spend some much needed time practicing!



    I want to offer special thanks to @tubegeek , @andrewRneumann , @Lowerleftcoast , @King Fan , @screefer , @awasson , and @D'tar for their help and patience with this build and troubleshooting.

    Okay, now to go play!
     
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  14. tubegeek

    tubegeek Friend of Leo's

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    @TeleSlug betcha can't build just one.

    Nice soulful playing - have fun!
     
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  15. jmp81sc

    jmp81sc Tele-Meister

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    Congrats on getting it up and running.
     
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