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joehpj

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Posts posted by joehpj

  3. stax t8000 clone (well sorta)

    in Do It Yourself

    Posted · Edited by joehpj

    I always wanted something that can beat T2 output power. 2SC4686 has been obsoleted and need 3/ch to do 500V/20ma. I check the datasheet, c4686 has 2.2pf output capacitance so it will be 6.6pf in total. Fairchild announced SiC BJT but was never available on the market. GeneSiC has some available on the market with some silly price. Among those, this has the lowest Coss. http://www.genesicsemi.com/images/products_sic/sjt/GA04JT17-247.pdf 16pf Coss about 2.5 times than c4686. 

    But I don't know why this thing should be BJT(alike?) but those pin out are labeled as DGS. 

    BTW. series caps are need for 600V and means we'll need 4x caps than 450V to get the same capacitance. Much more expensive to build. I don't know if this has that much difference on the sound. Normally no one will and should drive it to clipping.

  4. stax t8000 clone (well sorta)

    in Do It Yourself

    Posted · Edited by joehpj

    I googled for some substitute for c4686 which has been obsolete. And found MJW18020 seems to be a nice current production one. 1kv Vceo with much higher Pd makes it easier to do 500V 25mA. Any thoughts? 

    Edit:No. output capacitance way too high.

  5. stax t8000 clone (well sorta)

    in Do It Yourself

    Posted · Edited by joehpj

    I wonder if it's possible to add a voltage dropper like megatron did to lower 1156 and 5026 Pc and push the output voltage a little bit further? Say 475V~? ( I assume 10M90S+DN2540 can take 950V in total to be safe.) Or even -500V since EL34 output will need approx 35V across the tube.

  18. The Multi Amp aka Dynalo Mk2

    in Do It Yourself

    Posted

    Those were a GB ang728 and I ran locally. It was supposed to be silver, or grey, or gun metal - at least in our imagination. We ordered something like that. When the factory gave us some pictures of those...Say 30 of those. It's simply too late.:P It was done by accident and I assume it's impossible to reproduce again. I believe something was wrong in that anodizing sink. Who knows. I love them a lot.:D Because of the color, the power indicator is also green.

    DSC_6932.jpg

     

    • Like 1

  19. grounded grid

    in Do It Yourself

    Posted

    On 2017/3/31 at 0:51 PM, Pars said:

    I assume these cases are from China? Any hint as to who/where they are from?

    Everytime I see one of your pics, I keep thinking I like those... :)

    Those are indeed from China. I have some spare.......so PM me for detail if you are interested :). 

  20. Blue Hawaii BJT Build thread

    in Do It Yourself

    Posted

    16 hours ago, livewire said:

    BH BJT BOM MOUSER part number 80-PHE426PB6100JR06 references a .1uF /1kv cap.

    Is this a typo? (should be a 1uF / 450v cap as shown on the BH pcb silkscreen?)

     

    I copied from carbon BOM. Those are bypass cap so use whatever you want/have.

    1 hour ago, JoaMat said:

    The 33pF and 220pF need to be at a higher voltage? I use 1000 V Cornell Dubilier micas.

       

    My bad. should at least >400V to be safe.

  21. Blue Hawaii BJT Build thread

    in Do It Yourself

    Posted

    Here are my BOM for a pair of BH.

    https://www.mouser.tw/ProjectManager/ProjectDetail.aspx?AccessID=b44788bc7f

    for GRLV and GRHV. copied from Carbon build thread.

    http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=b6d687c7f7

    http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=54687aa8fa

    Parts I already have or going to buy from local dealer are NOT included like LEDs, insulators, IC sockets. Someone need to check if all resistor value are correct.

    I hope I could finish it at the end of April :D

    • Thanks 3

  22. grounded grid

    in Do It Yourself

    Posted · Edited by joehpj

    I think the final casing of the VR was done by same factory. Mine uses dale resistors. Or maybe they are really the same thing. I don't know (and don't care). I only care about the performance which was pretty nice for the asking price. I will have a chance to compare it with DACT. Will report if the difference is significant.

    I haven't heard GG now. It has been back ordered for months. :P

    According to the builder, both carbon and GG are TOTL amps. Overall performance are in the same league. Compared to carbon, GG has slightly recessed bass and tremble extension but sweeter mid and vocal. I've heard some people said 009 w/ carbon were too "clean". For those who think so, GG might be a better choice.

  23. grounded grid

    in Do It Yourself

    Posted · Edited by joehpj

    13 hours ago, Pars said:

    Looks really good. I like the case(s)... custom? Or off the shelf? Nice clean look.

    Semi-customized. The shape of front plate, depth, height, and heatsink was fixed. Others were customized.

    11 hours ago, jose said:

    Please, What kind of resistor do you use for grid?

    I used a KOA metal film (10K, 1 / 2w) but I can see that you used a different type (Carbon maybe???) . I'm in time to be able to change them and I would like be sure before pluging my GG.

    If you use my BOM, that would be 10k/.5w as you used. A experienced builder told me grid resistors were super hot because it was connected to the internal structure of tube. I later changed to 470R/3w, just because I have them in stock.  KG said the value doesn't really matter. T2 used 20k. BH used 470R.

    4 hours ago, bbest said:

    Nice looking assembly! All components fits on their places. Only volume control raises the question. It is EIZZ and there is long wires to it through the whole case. Does GG deserved this Chinese volume control ...

    Those were not EIZZ. Those were indeed from China. Building quality was good enough for the price. No issues like pop or clicking . There weren't much choice for stepped VR that were cased and no clicking. It has more steps in low volume area than DACT. Khozmos clicks. Goldpoint is expensive. I've bought over 10 of these. 

    For long wires, as you could see, there's no place for extension rod. Even I could move the amp boards a little bit, it would still need to redesign the back plate that means I have to throw away the whole batch. The wires were shielded and power supply were in another box. No worries. B)

  25. KGSSHV Carbon Build Thread

    in Do It Yourself

    Posted · Edited by joehpj

    Chassis are semi-customized and buttons are also from the manufacturer. Separated PSU theoretically would prevent 60HZ AC noise. The reason I use separated box was much simpler.... Because it's hard to fit GG in one box or it would be HUGE. Since customized chassis has MOQ, I want carbon, GG, BH to share a same design to lower the cost of customized chassis.  I had to order a batch of those. So yeah, more amps coming.

    DSC_6710.jpg

    DSC_6713.jpg

    DSC_6703.jpg

    • Like 1
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