RobRob Bassman Micro mods validation

Discussion in 'Shock Brother's DIY Amps' started by Hyakuya, May 17, 2021.

  1. Hyakuya

    Hyakuya TDPRI Member

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    Hi guys

    I'm in the planning stages of a @robrob Bassman Micro LTP EF80 and thinking of adding a few mods. I've butchered the layout Rob provides with my plan and wanted to ask if some more experienced eyes can take a look to make sure I've interpreted the mods correctly.

    I've got a load of 6N2P tubes which I'd like to use but the filament wiring is different so I've added this switch.


    upload_2021-5-17_10-14-54.png

    3-Way Feedback switch with a 50k pot to adjust the heavy value.

    upload_2021-5-17_10-17-44.png


    Elevated 6.3v CT

    upload_2021-5-17_10-19-49.png

    Bright / Normal switch and Gain Boost mod using a 50k pot.

    upload_2021-5-17_10-20-41.png

    RAW control mod.

    upload_2021-5-17_10-21-46.png

    Here's the whole layout with my changes....

    upload_2021-5-17_10-24-19.png

    Thanks in advance... :)
     
  2. zeppelinofled69

    zeppelinofled69 Tele-Meister

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    Your filament switch design will not work, as the 12AY7 side puts a dead short on the heater winding when it's in the 6N2P setting. You have the two filament legs tied to the same switch lug, so they will always be connected.
     
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  3. zeppelinofled69

    zeppelinofled69 Tele-Meister

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    I would wait for someone else to confirm this as I just drew it up, but I think this will do what you are looking for... however you will need a 3pdt switch instead of that DPDT.

    EDIT: Another thing to consider is all of the pinouts I have seen for the 6N2P have pin 9 tied to ground. I am not sure if this is needed, but you should definitely keep it in mind. I have added an option with a 4pdt switch that would cover the ground scenario.
     

    Attached Files:

    Last edited: May 18, 2021
  4. dougsta

    dougsta Tele-Meister

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    I've used a DTDP for the filament switch and didn't bother with the screen ground option.

    filament switch.jpg
     
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  5. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    InkedHeater Switch_LI.jpg
     
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  6. zeppelinofled69

    zeppelinofled69 Tele-Meister

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    Ah, see. I knew someone could do it better. I always have a hard time getting my switching as simple as it could be, but there ya go... a few different ways.
     
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  7. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I am right there with you zepp, now I am waiting for someone to do it better.:)
     
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  8. Hyakuya

    Hyakuya TDPRI Member

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    working out how to wire that switch was driving me round the bend and the short was spotted soon after I posted.... Ended up with this.

    upload_2021-5-19_13-31-11.png


    I'm thinking about adding adjustable bias to the EF80s as well now....

    upload_2021-5-19_13-32-54.png upload_2021-5-19_13-36-12.png
     
    Last edited: May 19, 2021
  9. robrob

    robrob Poster Extraordinaire Ad Free Member

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    The NFB needs to connected to the speaker tip, not ground (G).
     
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