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Millett "Starving Student" hybrid amp

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  1. Secretninja
    I am not really familiar with tubes, but the one working seems to be about the correct brightness.  Tomorrow I am going to pull those resistors and see if that helps.  If not, I am probably going to be done with it and see if anyone wants it on for sale forums as is.  I am not quite a starving student, but I don't eat quite as well as I would like if you know what I mean.
     
  2. hellomoto


     
    Quote:


    Hello,
     
    Do you think my mofsets or my tubes are dead? How could I test them?
     
    Thanks for your help!
     
    Antoine
     
  3. ArtemF
    the correct way to test the circuit is to measure the voltages in key points.
    The cathode voltage should be >0 and less than a couple of volts,
    the grid voltage in this scheme must be equal to zero, and the anode voltage
    should be less than 48 V but greater than 40 (my guess, I don't have a specs
    sheet at the moment so I can't calculate the working I and U, but there should
    be some common sense in the analysis - the filaments must glow,
    the accelerating voltage must be applied, the grid must regulate the flow).
     
     
     
     
     
     
  4. hellomoto
    Thanks for your answer!
     
    When you talk about cathode/anode foltage, it's the voltage between the anode or the cathode of the tube, and the ground? And what's grid voltage?
     
    If my filaments don't glow, I guess I won't have the desired measures. I'll order some mofsets and replace them, to see if it's the problem.
     
    Thanks!
     
    Antoine
     
  5. ArtemF
    all voltages are measured with respect to the ground.
     
    The grid voltage in this connection should be = 0 (there's no voltage source
    at the potentiometer and the grid current must be negligible).
     
  6. ArtemF
    if the filaments don't glow that means either burnt filaments (measure them with Ohmmeter when the
    tubes are out of the sockets) or burnt mosfets or closed mosfets.
     
  7. hellomoto
    Thanks ArtemF for your help, that should help me figure out what the problem is!
     
    Antoine
     
  8. tabacaru
    Does anyone know if it's possible to use IRF840 mosfets instead of the IRF510? I only have one IRF510 lying around and don't want to order any right at the moment!
     
    Thanks!
     
  9. yellowjeep
    The IRF510s are actually available at radio shack, at least the one by me. They had 2 of them as of about 10 min ago. 
     
  10. chew
     
    Hi,
     
    I'm new to this forum, and I've just finished to build my own Starving Student amp.
     
    I now have a problem with the sound level. Even with the potentiometer set to the maximum, the sound coming from my AKG 141 isn't loud at all. Though the AKG is only a 50ohm impedance can. I tried with a Audio Technica ES7 rated at 32ohm and it's a little bit better but not sufficient.
     
    I checked voltages, and some seems quite low. I get only 10V at the heater whereas it is written 12v on the schematics, and 13.5V at R2/R3/R4, but I've read in the thread that I have to get 17V there.
     
    These voltages are the same on both channels.
     
    I can see that the tubes are lightning but it's not as bright as I've seen on some pictures.
     
    Does it mean some values of my components aren't correct ? 
     
    Here's my BOM :
     
    Thanks BOM.png
     
  11. Beftus
    Add the cathode bypass capacitors (C7,C8). It will increase gain.
     
  12. the_equalizer

     
    Quote:

     
    I doubt bypass caps will help, the voltage at the MOSFET gate is too low. The low heater voltage is a consequence of the gate voltage being low. What's the voltage with respect to ground at both ends of R13 ?  it should be ~48 at the end connecting to C1 and ~45 at the other end.
     
    If those voltages are OK, I'd then unsolder one end of R2, R3, R4 each and measure their values. Same thing with the other channel.
     
    cheers!
     
  13. ouldsmobile
    thinking about trying this project out. would it work good for PC gaming?
     
  14. Ikarios


    Quote:


    I use mine with K701s for gaming but it mostly depends on what kind of headphones you have. The effect of the amp is miniscule compared to the effect of the headphones.
     
  15. marcus76
    Hi there...
    Oh well, just finished soldering all the parts together, what a mess!!
    Thought using a Star Ground like this  http://mark.rehorst.com/LM3886_amp/amps_chips_and_star_ground.jpg
    would be a good idea.. It wasn't. Loads of extra wire... [​IMG]
     
    Would it be a bad idea if I used a solid copper plate (1,5mm thick, found that @ work) , connected to the Star Ground
    and this plate to the Case or would a strip of it fit ?
     
    btw, I went a little to generous with the wire lenght which resulted in some nice noodle salad, guess that's ok? 
    But i got spare parts...if anything's not working (and i bet there is) I have plenty of lenght to cut out and resolder [​IMG]
     
    Cheers
     
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