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Millett "Starving Student" hybrid amp

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  1. Narwhalius
    Quote:

    Originally Posted by tomb /img/forum/go_quote.gif
    Unfortunately - agreed.



    Would this fit?
     
  2. tomb
    Quote:

    Originally Posted by Narwhalius /img/forum/go_quote.gif
    Would this fit?



    No - you need to order the one that's on the SSMH BOM.
     
  3. Narwhalius
    Quote:

    Originally Posted by tomb /img/forum/go_quote.gif
    No - you need to order the one that's on the SSMH BOM.



    Ok its ordered. So any advice on desoldering this thing? This is my first experience with soldering so I don't know much about it.
     
  4. Juaquin
    If possible, cut off the broken one and then worry about removing the leads from the holes. Heating 6 holes at the same time and trying to pry it out would be near impossible.
     
  5. tomb
    Or ... add solder on the bottom so that the blob is big enough to cover all 6 pins at once. That way, your soldering iron has a chance to melt all of the solder at once. If you're lucky, the pot will drop right out. If not, tie a string on it and pull while you're holding the iron to keep the solder melted.

    Once it's out, clean up the solder with braid, etc. Use lots of extra flux with the braid. To get the solder out of the holes takes practice and is a bit of an art, but again - add solder. You should have convex surfaces over the holes instead of concave. When you add the solder, the idea is to get the solder and the heat equally mixed, top to bottom through the hole. That way, when you get the braid wicking properly, it will suck all of the solder out of the hole.

    To aid in wicking, use lots of flux, but you can also make certain you have a bit of melted solder on your iron tip - that will "prime" the wick and give it a better chance to suck up all of the solder.

    Good luck.[​IMG]
     
  6. Juaquin
    That's a pretty big blob of solder, but that's definitely an easy way to get it off [​IMG]

    Just don't splash any on yourself!
     
  7. timmyGCSE
    n00b question alert

    how hot does the heatsinks get? i.e....how much heat will get transfered to the surface which the heatsinks are mounted on?

    basically is hard plastic, like the type you would find a..say..umm..games console made out of..a bad idea for case material?

    edit: oh and I'm dead excited now..I have all the components ready to rumble and my tubes came this morning [​IMG]
     
  8. Juaquin
    If you wanted to you could use plastic for the case, but the MOSFETs themselves must be connected directly to a metal heatsink. Connecting them to plastic is a sure way to fry the MOSFETs (or at least force them into thermal protection mode).
     
  9. tomb
    Yep. You're looking at each MOSFET dissipating over 2-1/2W each - that's not a small amount. The sinks we chose for the SSMH kit don't look like much, but they're actually sized for large, TO-3 type transistors and are rated quite a bit higher than most extruded sinks.
     
  10. the_equalizer
    There's also the fact that timmyGCSE is building a 12AU7 version, so the MOSFETs will be taking an extra 7 volts....

    So you need good heatsinks timmyGCSE. [​IMG]

    Ah! and don't forget that if those heatsinks are electrically connected to the circuit's ground, the MOSFET's need to be electrically isolated from the heatsinks (with mica spacers or something like the Beezar MOSFET mounting kits.)

    cheers!
     
  11. studwo
    wondering where can i buy this tube amp's kit set ? how much is it ?
     
  12. tomb
    Quote:

    Originally Posted by studwo /img/forum/go_quote.gif
    wondering where can i buy this tube amp's kit set ? how much is it ?



    Sorry, they're no longer available. The PCB's ran out and there aren't enough tubes on the market to support another production run.[​IMG]
     
  13. UKToecutter
    Tom,

    Perhaps you might consider putting together a 12AU7 version of the kit?
     
  14. timmyGCSE
    Quote:

    Originally Posted by the_equalizer /img/forum/go_quote.gif
    There's also the fact that timmyGCSE is building a 12AU7 version, so the MOSFETs will be taking an extra 7 volts....

    So you need good heatsinks timmyGCSE. [​IMG]

    Ah! and don't forget that if those heatsinks are electrically connected to the circuit's ground, the MOSFET's need to be electrically isolated from the heatsinks (with mica spacers or something like the Beezar MOSFET mounting kits.)

    cheers!




    in the end I decided on a wooden case type thing..I will reveal all hopefully tomorrow..don't expect to be in shock and awe though, it looks aiight but nothing special and I'm not the tidiest wiring person in the world. And yes the heatsinks will already be isolated from ground

    I'm about 75% of the way through..I have the MOSFET's to wire, 5 ground points and erm..ahem, I bought 330K resistors instead of 33K so I need to make a long old trip to Brighton tomorrow to get some 33K's. But my newly bought today soldering iron packed up anyway (What.. :-/ ) so I have to take that back and get another too. ah well

    edit: ah just something..in your original 12AU7 post where you explained the pin mappings you said it needed r2/r8 to change
    Quote:

    The required resistor change is R2/R8 = 390 Kohms. This moves the voltage at the MOSFET gate to compensate for the heater voltage dropping from 19 to 12 volts.



    whereas the post a couple of pages back with advice you say R4/R10. Does it matter or can it be either?
     
  15. the_equalizer
    Quote:

    Originally Posted by timmyGCSE /img/forum/go_quote.gif
    <snip>

    edit: ah just something..in your original 12AU7 post where you explained the pin mappings you said it needed r2/r8 to change


    whereas the post a couple of pages back with advice you say R4/R10. Does it matter or can it be either?




    You're absolutely right, my apologies. Indeed it is R2 and R8 that need to be 390 Kohms.

    cheers!
     
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