First Build - Rob Robinette Micro Champ

Discussion in 'Shock Brother's DIY Amps' started by SJK45, Aug 14, 2020.

  1. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I also wonder if the reverb driver is designed to attain low frequencies. A OT design should be interested in the low frequencies. A reverb circuit doesn't need them.
    Is the air gap of a single ended OT and reverb driver similar. IDK a transformer winder to ask.
    So as I said earlier, I would feel more comfortable using a transformer designed for audio but I have no basis for an informed decision. Just a hunch.
     
  2. jvin248

    jvin248 Poster Extraordinaire

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    Keep that nervousness, it will protect you.

    Triple check the orientation of the electrolytic caps, if you reversed the polarity by accident they will go off like firecrackers.

    Build a 'light bulb limiter' as shown on the Uncle Doug youtube channel for when you first fire up the amp. Also build a capacitor discharge tool like shown on the youtube d-labs channel. Capacitors retain their full voltage to release in an instant (remember those disposable flash cameras? They charged up a capacitor to give the instant flash as a chemical battery could not discharge fast enough).

    .
     
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  3. SJK45

    SJK45 TDPRI Member

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    Thanks guys, and Rob - no need to apologise at all - fantastic having such great information on your site. I wouldn't be doing this at all if it wasn't for you!
     
  4. SJK45

    SJK45 TDPRI Member

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    I think I get the wiring although I'm not sure of the reasoning! I'll sit down to try to figure it out.

    I'm also going to swap the 270 AX for either the Hammond 369HX - or the tube-town toroidal. Would either of these work or would one be preferable to the other? The 369HX is pretty expensive here £110! from Mouser.

    I'm going to solder most of the board tomorrow. I'll post an update then.

    Thanks so much everyone for your help.
     
  5. andrewRneumann

    andrewRneumann Tele-Holic

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    Great! Have fun and take your time. Send pics of the top and bottom and let us see your masterpiece.
     
  6. Paul-T

    Paul-T Tele-Meister

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    I'm hoping others will comment, too, but my choice would be the tube-town, for reasons of budget. As mentioned, that's what I'm using on my Deluxe micro.

    If you want something more traditional, I believe others have also used the Reverb power transformer in Micro builds, like this Hammond 261D6. Again, it's a 250V secondary, but a slightly larger dropping resistor would put you in the right ballpark. @robrob , would that be ok, given the 369HX is over double the price?
     
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  7. SJK45

    SJK45 TDPRI Member

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    I’d be in interested to know this too!
     
  8. SJK45

    SJK45 TDPRI Member

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    Ok - this is the component board. I’ve only ever soldered pickups before so.....

    I still don’t have the 25uf caps so they are not on there yet. Next time I’m going to lay out the wires before i start!

    Anyone know what the shiny bits are around the eyelets. I’d like to avoid those next time.

    I’ve left random (hopefully long enough) lengths of wire since I haven’t really thought about the chassis yet.

    I realise I haven’t done the ground yet - don’t have the bus wire!
     

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  9. robrob

    robrob Poster Extraordinaire Ad Free Member

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    The Tube Town toroidal and the Hammond D261D6 will work but they don't have a high voltage center tap so you will have to use a bridge rectifier. You can buy a packaged bridge rectifier or build one using 4 diodes.

    You can create a bridge rectifier using the 4 diodes you already have on the board. Add a jumper to close the loop in the rectifier and that will be the ground connection. The two high voltage wires will connect to the top and bottom eyelets and the DC out will be the eyelet opposite the ground connection.

    [​IMG]
     
    Last edited: Aug 16, 2020
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  10. andrewRneumann

    andrewRneumann Tele-Holic

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    I think you are referring to the rosin flux. Hard to avoid as it’s built into the core of your solder. Some isopropyl alcohol and a small stiff brush should remove it.
     
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  11. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I concur. Cheap and easy. If the mounting is doable and the voltage/amperage numbers fit, why not?
     
  12. SJK45

    SJK45 TDPRI Member

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    So would that mean adding an additional ground wire as per red line in the photo (or is it the other end?)
     

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  13. Paul-T

    Paul-T Tele-Meister

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    Not quite. It's wired like this:

    valve PT .png

    If we're discussing the tube-town (or any PT without a centre tap), info sheet tells us:

    Pri: 0-220-230-240 V (schwarz-gelb-lila-rot / black-yellow-purple-red)

    Sec 1: 250 V @ 0,12 A (red / rot)
    Sec 2: 6,3 V @ 3 A (green / grün)

    We connect, on the primary, balck and red to the switch (if we're in the UK)

    The secondary has two red wires. Those are essentially the two from the secondary shown on the diagram above, so one red wire would go to the top juntion of the two diodies, and the second red wire would go to the bottom junction.
     
  14. SJK45

    SJK45 TDPRI Member

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    If we're discussing the tube-town (or any PT without a centre tap), info sheet tells us:

    Pri: 0-220-230-240 V (schwarz-gelb-lila-rot / black-yellow-purple-red)

    Sec 1: 250 V @ 0,12 A (red / rot)
    Sec 2: 6,3 V @ 3 A (green / grün)

    We connect, on the primary, balck and red to the switch (if we're in the UK)

    The secondary has two red wires. Those are essentially the two from the secondary shown on the diagram above, so one red wire would go to the top juntion of the two diodies, and the second red wire would go to the bottom junction.[/QUOTE]

    Ahh, thank you. So is it more like this?
     

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    Last edited: Aug 16, 2020
  15. SJK45

    SJK45 TDPRI Member

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  16. Paul-T

    Paul-T Tele-Meister

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    I personally think it's perfect but maybe check with Ampmaker?

    He says:"The heater supply secondary is a non-CT 6.3V rated at 1A. This makes it perfect for an amp using two or three 12AX7s (or quivalent. I have also tested it with a single ECC83 and a 12AU7/ECC99 configured as a push-pull amp for 1-2W output together with the 4W output transformer. (Note that with an ECC99, the total heater supply runs slightly over-spec at 1.1A, but the transformer has a 15VA core and handles it well enough.)

    If you're using Rob's normal ECC82 aka 12AU7, that has a smaller current draw so looks to be fine.

    It's a fairly clear delineation between that and the tube-town, the tube-town has way more oomph - but you don't really need it, while the Ampmaker is tiny and beautiful, its main drawback being if you don't like your build you couldn't use the ampmaker with anything but a micro-amp.
     
  17. D'tar

    D'tar Friend of Leo's

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    20200816_110141.jpg
     
  18. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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  19. SJK45

    SJK45 TDPRI Member

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    Thanks so much that's very clear - it also look as though I need to remove (or effectively move) the two red power wires going from the two central diodes?
     
    Last edited: Aug 16, 2020
  20. D'tar

    D'tar Friend of Leo's

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    Yes, move the HT wires....

    With PT HT CT

    20200816_131139.jpg

    Without CT and with bridge rectifier....

    20200816_130600.png

    20200816_130820.jpg
     
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