5f4 / 5e7 build

Discussion in 'Shock Brother's DIY Amps' started by theprofessor, Feb 2, 2019.

  1. King Fan

    King Fan Poster Extraordinaire

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    hmm see below
     
    Last edited: Oct 11, 2019
  2. King Fan

    King Fan Poster Extraordinaire

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    Benvenuto, amico. :)

    You're right, good eye... those small upgrades and updates are all potentially useful.
    • Adjustable bias -- a very useful, convenient way to help you set your amp to run 'best.' Not a mod to the original sound, but a modern way to avoid having to replace resistors to set the all-important power tube bias to save your tubes and get the best sound.
    • Rectifier diodes -- these are simply protection against possible tube failure damaging your circuit. Easy, minor, and definitely will not alter the sound.
    • The 470R 'screen resistors' from pin 4 to 6 on the power tubes are an 'update' that adds protection and may improve the overdrive tone.
    • If I'm seeing right, the 1.5K control grid resistors connect to the 220 K either way. Recall pin 6 in inactive in these tubes, so that lug is just a tie point. Tying it to pin 6 is probably more physically stable than hanging it in the air.
     
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  3. ginomolinari

    ginomolinari Tele-Meister

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    Grazie!
    Ok, think I’ve got the gist. But I cannot see from the updated layout what kind of diodes are used and the pins to connect them to. Can you shade some light?
    Thanks.
    i am ordering some missing parts and I will start a new tread on my build. Hopefully it wont look too amateurish. :)
     
  4. King Fan

    King Fan Poster Extraordinaire

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    For the diodes, and in fact all the items we discussed, you can hunt up good info on Rob Robinette's amazing pages, especially on 5e3 and 5f6a mods.

    upload_2019-10-11_15-2-44.jpeg
     
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  5. BigDaddy23

    BigDaddy23 Tele-Holic

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    ^ This.......

    Rob's pages explain all of those tweaks and are immensely useful to any amp builder.
     
  6. ginomolinari

    ginomolinari Tele-Meister

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    Thanks guys. I have been reading alot on his website. I didnt think those mods were compatible with different amps. I guess I have a lot to learn.
     
  7. theprofessor

    theprofessor Poster Extraordinaire

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    Well I'm not not doing that again! That is, I'm always doing this:

    I added the 1Ω 1% tolerance resistors to the power tube sockets between pin 1 (which is tied together with pin 8) and ground. I have tried other ways of taking bias measurements, and this is by far the easiest. Get your plate voltages in DCV from pin 3 on each power tube socket, then measure across the 1Ω resistor (from one end of the resistor to the other) in DCV, which will give you a negative number but which will be identical to the plate current in mA as a positive number.

    IMG_2441.JPG
     
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  8. D'tar

    D'tar Friend of Leo's

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    Best $1 component addition to any fixed bias circuit!:D
     
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  9. theprofessor

    theprofessor Poster Extraordinaire

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    Agreed! I ordered 20 of them from Doug Hoffman, just to have them on hand for this very purpose.
     
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  10. King Fan

    King Fan Poster Extraordinaire

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    You said it, Prof. And of course I agree with @D'tar . Best simple mod in the universe.
     
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  11. Paul G.

    Paul G. Friend of Leo's

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    I don't do this (yet), but I know a guy that does. Get a red sharpie. When all soldering is complete on a turret (or eyelet), and checked, then add a red dot.
     
  12. theprofessor

    theprofessor Poster Extraordinaire

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    That's a really good idea. Thanks! It's easy to lose track, especially when there are a lot fairly close together, and they're not laid out in a linear fashion.
     
  13. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

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    I do this on a paper layout... I use different color pens for different steps. As I lay out all the components and jumpers, I mark the length of the wire or component, then mark each solder joint as it's done as well. Adds a little time to the front end, but has spared me untold hours of troubleshooting on the back end!
     
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  14. Tom Kamphuys

    Tom Kamphuys Tele-Holic

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    I use the transparency in DIYLC. Everything processed is set to 10%. Things you forgot pop out.
     
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