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Millett "Starving Student" hybrid amp

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  1. the_equalizer


    Nice work! Congratulations on getting a 6J6 variant up and running! 


    0.22 uF @ 100v will do nicely for C2, C4  and C3a, C5a
    EDIT: of course, 0.22 uF @ 200v will also work perfectly.
  2. wiisus
    Thanks for the reply!  After reading 100 pages of posts, I'm getting very excited to build this.  Placing parts order tomorrow.
  3. Rangiroa
    Ok guys,
    I have finished putting together the amp using the_equalizers 12au7 method. I will post pics but im highly embarrassed of my wiring skills. Its a hot mess.
    And thats probably why I am having issues, TBH.

    I did a little search beforehand but because I am using a different tube than 80 percent of the thread talks about I feel more comfortable just asking for help :)
    Anyway, When i first plugged in the amp the power switched sparked, and sparked a couple more times but once it got turned on the tubes were glowing like they should have. I believe a grounding issue caused the sparks. I am led to believe that everything was connected correctly at first because the tubes appeared to be working as expected.

    I then proceded to try and fit everything into my case and that is when things got screwy. Now, my power switch regardless of whether its on or off allows the tubes to heat up. It could also be that the tubes take a little while to lose its glow. I built the amp with all the sides unscrewed so i had more room to work, instead of building it inside with walls all in place.
    After I did some more fiddling to make sure no wires were touching any other part of the circuit, now only one tube is lighting up, and its brighter than normal and sometimes flickers in and out. It appears that all connections on the tube sockets are solid.
    I have not hooked a source or phones up yet, just tryign to get these things out of the way.

    I cannot post a pic until later this evening when I get off work, so if you need a pic it will have to be later today.
    Could it be possible that a resistor is touching the aluminum case and is grounding out part of the circuit or shorting something?
    Could my power switch be causing all these weird problems, and I need to get a new one? Should I insulate all open resistor metal so they don't touch the sides of the case?
    Is there a way to use my DMM and find where my problem is? im not exactly comfortable using the DMM, I have only used it for tube biasing.
    Its a tight fit for everything in the case and I am sure that is causing my issues.
    Any tips, or ideas would be appreciated, I spent a long time last night working through the kinks on this and now im stuck.
  4. ArtemF
    Did you measure the voltages in the key circuit points? What were the results?
    I'd suggest disconnecting everything except the heaters and to make them working properly.
    After that one can move further.
  5. Rangiroa
    Thanks, I will try that, as fun as that doesnt sound :)
    I don't leave the amp on long enough to check voltages because the tube lighting up seems unnaturally bright and i dont want to burn it out.
  6. tomb


    I think the answers to all your questions are, "yes."  Because there are so many of them, though, IMHO a pic will do us the most good.[​IMG]
  7. nightarya
    Heya Head-fi
    First time poster here, been looking at thist hread for quite some time to make one of these puppies.
    But anyway, i made a 12AU7 version of this amp, plugged it in, turned it on. Then....nothing.
    I've went through most of the connections with a multimeter, NOTHING. I find no issues with my soldering job but either way, my tubes aren't doing anything. Nothing. They're not heating up, no audio, nothing.
    Is there something wrong with the way i soldered this? This is just the 12AU7 schematic (the one with the swapped out pinouts & 390k resistors)
    Pictures included to see if you guys can help me at all...i really want to know what i messed up >.<
    117_0208.jpg 117_0209.jpg 117_0212.jpg
    Any help you could provide would be greatly appreciated! Thank you guys! Please don't tell me my tubes are fried because i wired them wrong >.< Please.... I'd hate myself if i did.
  8. wiisus
    I don't know gallons about electronics, but it looks like some of your solder joints might be touching the case...I don't think they should be, as your case isn't the ground...

    I'm not sure if I'm fully correct on this, just my guess. 
  9. Ikarios
    So I spent most of the day thinking about my AlienDAC -> Millet build, and figuring out all the little bits and pieces I needed to get the whole thing set up in one big shot whenever I'm ready. I drafted up a really basic schematic interpretation; tomorrow I'll refine it and turn it into my draft enclosure layout for a P2P 12AU7 build. First, I need to get these questions out of my head before I forget some.
    1) how exactly does a bypassing capacitor work? Do you just run a film cap in parallel with whatever cap (generally electrolytic?) you want to bypass? I notice the schematic shows C3a and C5a as what I think are bypass caps; are the Wima film caps in the BOM good enough for this or should I spring for something like the Beezar VitaminQs?
    2) I spent some time wrapping my brain around what the tube looks like in the schematic. If I'm reading this right, pins 2/7, 1/6, and 3/8 are essentially bridged, right?
    3) If I want to build a version that switches between RCA and 3.5mm mini inputs, I'd want to use a DPDT toggle, right?
    4) The BOM calls for a 50k pot; I have a couple of 10k pots left over from my CMoy build maybe four years ago :)O), including the Panasonic recommended in Tangent's guide and an Alps RK097. Can I use these pots simply by modifying values of R16/17 to 10k instead of 50k?
    4a) which resistors are the resistors that affect the gain? R16/17? If I wanted a higher gain version for use with 200ohm+ headphones or so, would I use 20-25k values?
    4b) how do most common gain toggles work? a DPST switch, two connections from the input jacks leading to both sides of the switch, one side with one gain resistor set and the other with another? is there any way i can do this with my input switching idea without running a giant mess of connections? gain is more important than input switching (which can be fixed by using the right IC), so I might just use the gain idea...
    5) how do most people mount tube sockets in a p2p build without a place for them to sit??
    5a) possibly answering my own question - would I want to use a socket like the third one down on this page (http://www.tubesandmore.com/scripts/foxweb.dll/catalog@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?PAGE=SUBCAT&SEARCH_TREE01=ZCATALOG&SEARCH_TREE02=2009013) and mount those metal tabs at the top to the top of the enclosure?
    5b) what's the difference between the different types of tube sockets? I think I get "chassis mount" vs "pc mount", but I don't know about top or bottom mount... or the differences in socket material, for that matter.
    6) do Mouser or Newark carry switch faceplates like these found at handmade? (http://www.hndme.com/productcart/pc/viewPrd.asp?idproduct=702&idcategory=127) I spent a while playing with their search filters but didn't come up with the goods. I think ideally I'd want a blank faceplate, as I have access to a laser cutter/etcher at work. I'd also like to be able to etch directly into the case, but at $20 a pop and without ordering replacement panels, this is probably a no-go seeing as how we'd probably have to use trial-and-error for figuring out the power of the laser.
    7) I see most people are using some type of copper sheet as their ground plane. I have some leftover sheets of galvanized steel sheet metal from Home Depot - will this suffice for a ground plane, or are the benefits of copper worth it?
    Phew... that's a lot of dumb questions for someone who hasn't even picked out all the parts yet. I'd revise and condense these, but it's getting late and I need to get to work tomorrow morning. Thanks in advance!
  10. ArtemF
    2 nightarya:
    what do you mean by "nothing"? No voltage at either of the points?
    What do you measure when the power supply unit is unplugged?
    (I mean, does it work at all? - it sounds stupid but I faced with many cases including the
    faulty connector that looked absolutely normal and new).
    Can you take a powerful resistor and plug it instead of your circuit to test the power supply?
    May be it simply "refuses" to work with this load.
    Can you test the resistance of the heaters? What changes when you plug the tubes to the amp?
    What is the resistance between the "plus" and "ground" wires of the circuit when the DC power
    cord is unplugged?
    If the system withstands these tests then you can go further and check the voltages in the key points.
  11. Rangiroa

     To answer #3, I only bridged 3/8 but 1/4 have 2 connections running to them.

    Then again, my tubes light up but i cant confirm anything works just yet :)
    To answer #5, I used chassis mount tube sockets to mount the sockets because they have flanges for a screw. I believe the PC mount tube sockets do not have flanges bc they are for use on a circuit board.

  12. Rangiroa
    Your soldering job looks similar to mine and I have your problem as well.

    I believe if you shorten some of those wires and snipping excess resistor leads, make sure and seal each connection with heat shrink (i am using electricians tape atm) it should hopefully work. shortening the wires reduces the chance for there to be any connections touching.
    I didnt study your actual soldering i just assumed you built it exactly like the schematic.
  13. Beftus
    I couldn't resist....
    Here's mine again, this time with tube LEDs. I installed orange LEDs to match normal tube glow instead of going for the popular Cherenkov-look. I'm running both LEDs @ 10mA.
    Yesterday I slipped two grease coated Kapton insulation foils between the IRF510's and the heat sinks. Thermal conductivity is much better now, the heat sinks are now ~58°C (136°F). Without thermal compound they were ~50°C. I may install 2.5" tall heat sinks in the future.
    I also applied some wood oil to the box to bring out the grain a bit. The more I listen to this puppy the more I love it.
  14. Ikarios
    Nice glow, Beftus! I'm probably going to run orange LEDs to my tubes as well, so thanks for supplying the mA info so I know what to expect. Still need to figure out how to wire up the LEDs, though...
    in your pic, your glow seems a little red. is that your camera or the LED?
  15. Beftus
    Read this one and the post following it. That's my source of information. Good luck.
    Here's why I chose 10 mA:
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