Newbie on DIY Amps - 5F1

Discussion in 'Shock Brother's DIY Amps' started by Scottsgarage, May 16, 2021.

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  1. Scottsgarage

    Scottsgarage Tele-Meister

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    I started a thread on the Glowing Tube forum where I ordered a Mojotone 5F1 kit in March, and as I am sure you all know supply chain issues with electronics (in this case the xformer) - I did get it impressively packaged and all recently and so now I embark on building it. On the other thread I got great advice and indeed have been cross checking with the Stewmac assembly instructions and RobRob's site to get started.
    I will say I will take 4x the estimated hrs to get this done, but that is part of it for me.
    It is a tight assembly. And I am not following the order of the Mojotone assembly instructions explicitly.
    And you TDPRI community are fabulous so you know.

    So now do you have to wait for power to be able to check if the xformers are ok? I am a newbie so don't be harsh. Can I ring them out with my multi meter?

    And it is challenging for me to get all the components and wires on the board and for them to stay there. I have been using masking tape, I mean the components are ok but all those wires in the large holes will move and fall out. Will get there. .. pic attached I have the card IMG_3372.JPG board layout but mojotone's real size diagram that came is really good.
    And I wanted to add the 25uF cathode bypass cap on the 12AX7 but the kit only came with one of those, so I will build without. I went to the local electronics store here in Santa Cruz and while they had some stock of basic components they did not have that value I was told not standard - was it more standard in the past?
     
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  2. J. Bonkosky

    J. Bonkosky Tele-Holic Silver Supporter

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    Hey! Looks like you are off to a good start. One word of advice would be to move the bypass cap and the cathode resistor for the 6V6 as far away from each other as possible. The heat from that resistor will murder that cap. As far as the transformers go you can check the with a multi meter. Make sure the windings a separate from each other and not grounded to the iron core. Beyond Thant not much you can do until they get power. Have fun!
     
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  3. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    Try curling the ends of the leads around other side of the eyelets so they can't fall out. It's good to make a secure mechanical connection before adding solder.

    Agree with the above about making some room between the cathode resistor and bypass cap -- good thing you haven't cut the leads yet. :)
     
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  4. kbold

    kbold Friend of Leo's

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    27uF is a standard value.

    The words 'newbie' and 'valve amps' in the same sentence concerns me.
    Do you know how to stay safe? (i.e. not killing yourself with high voltages)
    Can you employ an assistant (wife, child, etc) with 1st aid knowledge and/or a phone to speed dial for an ambulance?
     
  5. NTC

    NTC Tele-Holic

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    22uf is also standard and low enough that you won't hear a difference.
     
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  6. Scottsgarage

    Scottsgarage Tele-Meister

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  7. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    There is only a few volts at that V1 cathode terminal so even a 10V cap is fine. Ime a 2.2uF to 10uF can improve a 5F1 by reducing the low bass frequencies. Usually a 5F1 is rather bassy.

    The 25uF 25V cathode bias cap Fender used may have been a standard cap at the time. Leo bought in bulk. 25uF is not critical for this part of the circuit. A large-ish 25uF to 250uF capacitor will let AC find a way to ground. When a cathode cap is not used, gain is reduced and AC is on the cathode, so some negative feedback and increased output impedance will occur contributing some noise. On a guitar amp it is not enough noise to be concerned about. A smaller uF cap is used to shelve some lower frequencies. Jim Marshall did this quite often.
     
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  8. Scottsgarage

    Scottsgarage Tele-Meister

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    Thanks for your concern. I am a newbie at building amps. I have the background on electronics to stay safe.


    l
     
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  9. Scottsgarage

    Scottsgarage Tele-Meister

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    that's why I posted and I will be posting more and thanks!
     
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  10. Scottsgarage

    Scottsgarage Tele-Meister

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    Thanks that ' s informative .
     
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  11. Scottsgarage

    Scottsgarage Tele-Meister

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    0518 build.JPG
     
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  12. Scottsgarage

    Scottsgarage Tele-Meister

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    So here is this day's progress.
     
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  13. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

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    I’ve found success using a 4.7uF on that preamp cathode bypass (in 5F1s with the standard 22k Negative Feedback resistor on the board from the output jack).

    Those Champs are passing a lot of bass. They can get farty.

    Lower values start rolling off bass, while the NFB evens out frequencies further.

    For single coils, a 22 or 25uF fattens up the sound (a lot of tweed era circuits pass a lot of bass and mids, which is why a lot of Tele lovers like tweed Deluxes). But with humbuckers, some tweed circuits get flabby when cranked.

    So I tend to go with 4.7uF on mine, since I use both single coils and humbuckers.

    Some people cut further (0.68uF, 1uF, or 2uF), which basically acts to boost upper mids and highs. I find that sometimes makes my single coils not fat enough, but sometimes sounds good with darker humbuckers.
     
  14. harpdog

    harpdog Tele-Holic Silver Supporter

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    I recently built the same kit with about no experience. Fun and rewarding. I suggest reading and understanding all of the warnings out there concerning voltage.
    That, and keep wires as short as you can. I have to go back in and shorten some. First I will go over all of the capacitor discharge material.
     
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  15. Scottsgarage

    Scottsgarage Tele-Meister

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    Any comments on the use of 'vintage correct' wiring of the power xformer where Black and White go to fuse and back of volume pot vs 'Modern' where the Mojotone instructions are to connect Black to back of volume POt and White to the the power cord?
    The Stewmac build manual does the 'Vintage'.
     
  16. Scottsgarage

    Scottsgarage Tele-Meister

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    Thank you I will try that
     
  17. Scottsgarage

    Scottsgarage Tele-Meister

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    Thank you and I did that. It is a tight build I am getting along though.
     
  18. Paul G.

    Paul G. Friend of Leo's

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    The safest way to wire your amp, which, BTW, is the only scheme that complies with code in the US and Canada: Neutral (white) lead from your cord connects directly to one of the transformer primaries. Hot (black) lead from your cord connects directly to the center lug of your fuse holder. The side lug of the fuse goes to your switch. The other side of the switch connects to the other primary lead of the transformer. Ground (green) connects to the chassis on its own unique connection.

    Do this.
     
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  19. Scottsgarage

    Scottsgarage Tele-Meister

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    Yes that is what I did thanks for the confirmation
     
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  20. Heyhey

    Heyhey TDPRI Member

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