Anyone going to build coasters?

Discussion in 'DIY' started by sodacose, Jul 20, 2018.

  1. sodacose

    sodacose MOT: WTFAmps

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    This came up at the recent Milwaukee meet.

    http://www.schiit.com/products/coaster

    They come in a 4-pack and look like a cute little hybrid project. I'm thinking about putting one together as a review/article. I'm willing to split/ship PCBs and 6418s/6088s if people are interested.
     
  2. Skyline

    Skyline Double-blindly done with this hobby

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    Screw the amp. I just want the coasters.
     
  3. Cspirou

    Cspirou They call me Sparky

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    I'm building for sure. Trying to brainstorm a case for it. I have someone stopping by the schittr for me to pick them up. If you haven't bought them yet just let me know and I can send one over to you.
     
  4. sodacose

    sodacose MOT: WTFAmps

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    That'd be great if you have an extra. Happy to PP some funds.

    3.5in round. Would it fit in a tuna can?
     
  5. sodacose

    sodacose MOT: WTFAmps

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    OK, I just ordered a bunch of 6418s. I've been planning a portable project to test a battery + DC booster design anyways. Looks like a good sub mini candidate.
     
  6. Azimuth

    Azimuth FKA rtaylor76, Friend

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    I am trying to resist this, but I may not be able to.

    I even have a square R2-D2 case it would probably fit.

    Has anyone done a cost of parts yet. Maybe I can put out a project on Mouser this weekend. If I do, I will share the project link so all the parts appear in the cart.
     
  7. sodacose

    sodacose MOT: WTFAmps

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    I looked at the bom and didn't see anything remotely pricey unless the jacks/pot are some strange flavor. Tubes are a couple bucks a piece.

    Probably the wall wart/transformer is the most expensive part. AC wall warts aren't as common as DC smps.
     
  8. dBel84

    dBel84 Friend

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    A sad reflection on my hoarder quality, I still have a round tin that my SOTA pager came in.... In 1986

    There is little hope left.. dB
     
  9. Ringingears

    Ringingears Honorary BFF

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    I love it. Schiit humor at its best. And fun for geeks.
     
  10. Cspirou

    Cspirou They call me Sparky

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    They use wallwarts that Schiit uses for their DACs and amps. If you want to go over the top you can use a small 16 VAC toroid. Because they are both round they can fit in a soup can.
     
  11. Azimuth

    Azimuth FKA rtaylor76, Friend

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    I think the wall wart is going to be the most expensive part. You can get a Triad one from Mouser if you want to order the BOM at once.
     
  12. peef

    peef Friend

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    Looks like the tube idles at ~150uA, -1.25Vgk, and ~15V on the plate. Q102 idles around 5mA. It's a great transistor, but it's eating anywhere from 7uA to 25uA of the tube's current at idle depending on hFE. Might make sense to swap in a p-channel FET? Or to just run it cooler?

    A CCS on the plate would be nice since the tube really wants to see a plate load in the >50k range (datasheet page 2), just tricky to fit one on a small smd resistor's pads. One of these might work-- shorting pins 1 and 2 makes a 50-130uA CCS.
     
  13. schiit

    schiit SchiitHead

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    The tube actually runs at about 800uA as built.

    Other than that, yes, a CCS could improve performance. It would also increase gain, which may or may not be a good thing, depending on what you want to do with the circuit.
     
  14. sodacose

    sodacose MOT: WTFAmps

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    @schiit The 6418 triode curves I have suggest a much lower current with 30V B+ and a 10k load. Closer to what @peef was seeing. Do you mean the 6088 or is reality just that much different than the on paper calculation?
     
  15. schiit

    schiit SchiitHead

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    8V across a 10K load is 800uA, as far as I know. That's a typical result. Depending on the tube, it will vary, but I've never seen it less than about 6.5V or more than 9V, and that's with either 6418 or 6088 tubes.
     
  16. sodacose

    sodacose MOT: WTFAmps

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    Whoops, not only did I add a zero looking at the plate curves but it sounds like they don't reflect reality anyways. Thanks for the patience.
     
  17. peef

    peef Friend

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    I think the datasheet is OK, and we were both misreading it? One end of the filament is at +1.25V to heat it, but the other end is at ground potential. The triode curves show a plate current of 800uA for Vgk = 0V and Vka = 22V.
     
  18. Cspirou

    Cspirou They call me Sparky

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    Dangit! I had someone stop by the Schittr for me to pick up coasters and they didn't have them over there. So I just went ahead and ordered them.

    Suggestion for @schiit, could you add local pickup to online ordering? Places like Parts-Express and Monoprice have that option.
     
  19. Azimuth

    Azimuth FKA rtaylor76, Friend

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    Mouser parts - $28.50

    https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=73c2c3b4d6

    Everything but the coaster board, power adapter, and tubes.

    If you want to order the Triad wall wart equivalent, part number: WAU16-1000.

    I just realized in doing this cart that this is all SMD. I am probably out, except as enjoying as an actual coaster.

    PS - If I made a mistake, plase let me know.
     
    Last edited: Jul 22, 2018
  20. sodacose

    sodacose MOT: WTFAmps

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    Definitely makes it more challenging. At least there are no ICs with lots of pins.
     

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