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Millett "Starving Student" hybrid amp

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  1. rds
    Quote:

    Originally Posted by holland /img/forum/go_quote.gif
    [​IMG] How about you show me some measurements that there is no effect?



    No claims require no proof. If you're going to tell people this is causing distortion in their amps then back it up.
    The reason I twist wires is to reduce the EMI being picked up. Perhaps you should read this:
    Twisted Pair
    Quote:

    Originally Posted by holland /img/forum/go_quote.gif
    If you're an EE, you'll learn about the importance of layout eventually. But, if you don't, go into an interview and spout how it is not important and see if you get the job. You may be lucky and even see the effects in your first electronics lab at school.



    I don't think there's any need to be so condescending. You are clearly not an EE.
     
  2. holland
    deleted
     
  3. n_maher Contributor
    Guys,

    How about you step back a bit and calm down before you derail the thread to the point of requiring moderation?

    Layout absolutely matters, at the very least the ground path wiring can make a rather large difference. Look no further than my Menace thread for "proof", albeit with my ears used as the instruments of measurement. So as I said, chill, some parts of the wiring are less critical, others absolutely matter. If you want to wire it haphazardly (and my SSH certainly is no gem) go for it.
     
  4. dgbiker1
    Quote:

    Originally Posted by holland /img/forum/go_quote.gif
    Besides, tubes aren't the most distortion free devices, so I'm not sure how important the construction methodology really is. You're not really dealing with devices that have issues with wire capacitance or resistance from traces more than a mm in length between components, or having timing violations due to uneven traces and/or signal degredation, so...YMMV.



    Yea, I was just thinking about the stray capacitance and the inconsistent, relatively high contact resistance at each point. I know it can be a big deal in high frequency applications, I just wasn't sure how it would affect this kind of setup. A few pF ain't much, but I never know what a golden ear can pick up[​IMG]
     
  5. rds
    Quote:

    Originally Posted by n_maher /img/forum/go_quote.gif
    Guys,

    How about you step back a bit and calm down before you derail the thread to the point of requiring moderation?




    Yeah, I should have left this alone. I know wiring layout has an effect. I guess I just take issue with telling people that they need to follow these rules. In some cases the effect of messy wiring will add noise. I think with respect to this amp that is unlikely, unless intentionally done. Especially if you are using a metal case.
     
  6. trains are bad
    FWIW, while not an EE proper, I am a graduate EE student, and I assembled this amp in the graduate 'open' lab at the intense interest of three different uber-EE nerds, complete with flannel shirts and glasses, who seem to perk up when vacuum tubes are spotted. None of them mentioned the messy PTP wiring, and when I asked one of them if it was going to be a problem, only one of them suggested I keep the case closed so that none of the components got bent some direction and shorted. The issue of effect on the circuit was never considered worthy of attention.
     
  7. trains are bad
    For those of us that have completed an amp, I have a question

    Should I measure the currents going into the tubes? It's my understanding that usually you have to 'bias' amps after the tubes have burned in, by tweaking resistors in order to match the tubes or put them in their linear range, or to make sure too much current isn't going through the heaters.

    But I just basically bunged the amp together according to the schematic. This might be in the spirit of the design, but does the designer or someone with more understanding of the design have any advice for 'tuning' the amp? Or is this just not needed?
     
  8. dsavitsk
    Quote:

    Originally Posted by trains are bad /img/forum/go_quote.gif
    None of them mentioned the messy PTP wiring,



    It is likely less of an issue here as the PS is in another box, the voltages are lower than in most tube amps, and the Gm on the tubes is low due to the lower operating point, but wiring and lead dress in tube amps can and does make a huge difference. These are high impedance circuits with a propensity to pick up noise from lots of places, especially poor grounding. Take a visit to a dedicated tube amp forum and look through the daily posts of people trying to eliminate hum if you don't believe me. It can come from a lot of places and can take a lot of experience before building hum free amps happens regularly.

    Quote:

    Originally Posted by trains are bad /img/forum/go_quote.gif
    Should I measure the currents going into the tubes? It's my understanding that usually you have to 'bias' amps after the tubes have burned in, by tweaking resistors in order to match the tubes or put them in their linear range, or to make sure too much current isn't going through the heaters.

    But I just basically bunged the amp together according to the schematic. This might be in the spirit of the design, but does the designer or someone with more understanding of the design have any advice for 'tuning' the amp? Or is this just not needed?




    It is probably not needed, but is never a bad idea to at least have a sense of what is going on. I think the things you are most concerned with are the voltage across the cathode bias resistor, and the voltage across the heaters. It is possible that really imbalanced tubes will draw lots more current through one side, but that's really only something to worry about if you are operating tubes near their plate dissipation max where this would threaten the tube's life. But here, it probably doesn't really matter as there is nothing you can do about it, it would only cause you to pull the tube which would end it's effective life anyway, and you are nowhere near the max dissipation anyway, so it won't do any harm. If you have access to a distortion analyzer and or a scope, then you can adjust the voltage across the bias resistor to try to hit the lowest distortion level. I doubt you'll hear much difference, though.
     
  9. bhjazz Contributor
    Quote:

    Originally Posted by n_maher /img/forum/go_quote.gif
    Someone should have a closer look at 707-411626B25 from Mouser, I don't see any pins and I think that this part would be sufficient.



    One word: PINS!

    [​IMG]

    No worries. Just posting the answer to the question. I do have my eye on a particular metal case anyway, so this will work out just coolio.
     
  10. pinkfloyd4ever
    wait so those are the Comair Rotron ones?
     
  11. utilisateur
    Part Number says they are the Comair rotron ones
    They look identical to the FischerElektronik ones to me, maybe Fischer is Europe only though
     
  12. bhjazz Contributor
    Quote:

    Originally Posted by pinkfloyd4ever /img/forum/go_quote.gif
    wait so those are the Comair Rotron ones?



    Yes, sir.

    Comair Rotron Heatsinks

    The Mouser drawings are at an angle that doesn't effectively show the bottom.

    Edit: Just saw utlisateur's answer...oops. Ah well.

    Have a great day, all.
     
  13. Gross
    Hmm, I rebuilt mine to do a few changes and clean things up a bit, but now I have a problem...

    I accidentally had pin 1 on my mosfets (with R3/9 in place)wired directly to 48v and when I turned on the amp the tubes looked like light bulbs with 48v to the heaters. ( and you thought the PSU has a hard time starting up running the heaters at default voltage, LOL) Well, I discovered my problem and have reconnected the correct way on both tubes, at least it seems like that the 8 different times I have checked it out. However one tube still will light up the room upon power up. Is it possible to blow a mosfet in a way so it is always 'open'? Leaving everything else connected and just disconnecting the gate, or pin 1 of the mosfet, I get 45v on the side that isnt working properly, and 0v on the mosfet which is good. I suppose I have my answer, and upon reading up on mosfets it appears I have exceeded the gate to source voltage. I guess I am lucky I only blew one. Maybe once I replace it, i will realize the other one sounds like ass.

    That is my story. Moral, hook stuff up right.( If this post reads weird, it is due to the fact I discovered my problem halfway through typing it.)
     
  14. pmillett Contributor
    Quote:

    Originally Posted by Gross /img/forum/go_quote.gif
    I suppose I have my answer, and upon reading up on mosfets it appears I have exceeded the gate to source voltage. I guess I am lucky I only blew one. Maybe once I replace it, i will realize the other one sounds like ass.



    You are correct, sir - no doubt popped a hole throuigh the gate oxide. Just think of it as a learning experience.

    For the 50 cents or so that IRF510's cost, I'd replace them both.

    Pete
     
  15. Gross
    Quote:

    Originally Posted by pmillett /img/forum/go_quote.gif

    For the 50 cents or so that IRF510's cost, I'd replace them both.

    Pete




    Good thing I ordered enough parts for 3 amps, although I only plan on building 2.

    Here is an idea I am going to try, unless you guys think I should not. At this point I have a 100ohm resistor on the outputs, but obviously that can change how the amps sounds and damping and blah blah. I am still trying to reduce the output though, so how about throwing a resistor from pin 5 of each tube to ground to create a voltage divider on the input. I was thinking starting with a 10k or even 20k resistor on there, just to make the pot usable.

    ***Update***

    Well, I found a 100k pot I got from Jeff with Glassjar that I didn't use on my SOHA. I put that guy in, took out my 100 Ohm resistors on my output, and now I am a happy camper.
     
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