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livewire

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Posts posted by livewire

  1. Hi Tim,

    My efforts have been made possible by the owner of this thread, Doctor Gilmore.

    Yes, mine is the first prototype as far as I know.

    "Working prototype"? No, not yet. I have a ways to go.

    There are at least two others that I know of who are building the KGSSHV at the moment.

    They have not been posting much here, so I am not aware of their progress.

  2. Ok, after studying other similar power supply designs,

    in order to continue with psu troubleshooting, I think that a viable workaround has been found.

    Im gonna remove (for now) the 2sc4686a sand and the battery sub-circuit in the negative rail

    and replace it with a zener diode string. (150v-150v-150v)

    Hello (again) Mouser! Will update in a week or two...

  3. Is this the same board that got fried twice? I know you don't want to hear this but if it were me I'd repopulate on a new PCB since it was working before it got fried so that means there shouldn't be any errors in the PCB, pre-fry. And since the positive and negative rails are basically the same, other than deriving the bias from the positive rail, if you can't spot the problem on sight it may take a really long time.

    If you don't want to go that route, maybe post up some pics?

    Yes it is the same pcb that I fried twice, and the only one I have left.

    I'm almost to that point in this build.

    Not ready to go there yet, I still think that if I glean a little more knowledge

    maybe I can localize the trouble spot.

  4. Some observations and ramblings follow.

    I've been pouring over the datasheets to better understand the operation

    of the mosfets in this circuit. I see that the 10m90s that is ahead of the pass regulators

    is configured as a current source regulator. When switched on by the battery,

    the 2sc4686a transistor feeds the gate/kathode of the 10m90s as well as the gates

    of the paralleled fqpf8n80c series pass regulators.

    It seems that the pass regulator is not "turning on".

    My questions are:

    1) what should the output voltage of the battery be to the base of the 2sc4686a?

    2) what should the three mosfets gate voltages be? (as supplied by the 2sc4686a)

    3) is there any way to bypass jumper parts of the circuit to get it to operate?

    4) am I looking in all the wrong places?

    One last observation / question for now is the negative rail is only outputting -15 ~16VDC.

    Is this a intended minimum "leak-by" voltage to drive the battery?

    I'm really not getting how this battery thing works.

    The mirrored, cross-connected, cascaded transistors that comprise it are throwing me a curve ball.

    Thanks in advance for any suggestions, answers or insight that any of you gurus may have.

    kgsshvpower3(final).pdf

  5. In a word, yes.

    I've replaced almost everything on the negative side

    Cross checking against the good +450 volt side is difficult

    due to the groundplane linking everything when hot.

    If there were two separate identical 1/2 psu boards instead

    that were linked like in the schematic, it would be more straightforward for

    newbie comparison testing. It was working originally, so my goofs created

    a hole that I must now crawl out of.

    Knowing some testpoint voltages at the regulators

    and battery for instance could shed some light on the trouble spot(s).

    I wanna say "I'm done, stick a fork in me", but i'm not there yet.

  6. inu sent me these which are variations on the srx circuit.

    http://earsp.web.fc2.com/log/stax-r/stax-r-3.pdf

    warning, the 1150 volt version is only for those that

    really know what they are doing. And obviously the

    output caps need to be rated for 1200 or more volts.

    With respect to high voltage electrolytics, and also

    mylar caps, a resistor across the cap is pretty much

    required at all times. Even if you discharge the

    cap, and then remove the resistor, the capacitor

    will self charge, usually to very dangerous voltages.

    The higher the rating on the cap, the worse it gets.

    Words of wisdom! (regarding the caps)

    Can anybody here translate the japanese?

    I'm sure just viewing the schemos is all KG needs to see. :D

    Rest assured, I wont be messing with any of that HV tube stuff.

  7. I was definitely going to check with a dmm before handling, but I didn't want to set up the psu here at the lab and have to stick around for an hour before things were safe to handle.

    400V is the most I've worked with here at the lab so far, and it was more than enough to kill me at the currents I was working at. I'll definitely be keeping track of anything I touch. My plan is to use two DMMs, one on the positive rail and one on the negative rail, and attach probes before turning the psu on so I don't have to worry about exposing myself to the HV supplies.

    That is a good idea, keep in mind that if the psu does not utilize bleeder resistors,

    your DMM will act as one due to it's internal (high) impedance.

    The bleed-off time if noted, will only be valid for bleed down with that meter attached.

    At least you will know when it has become discharged and be safe to handle.

  8. @DQ, Some may think this is excessive, when I work with high voltages like this

    I have a ground strap attached to each arm and the device under test

    and perform the work while using a nonconductive rubber mat underfoot & on the workbench.

    I make a lot of mistakes, like slipping with the test probes, some of which are chronicled here on HC.

    I dont want a multi-hundred volt charge crossing through my heart, if you get my drift.

    On the job as a maintenance electrician, I have been shocked many times.

    Using safety procedures like these has probably saved my bacon numerous times.

  9. I can only speak regarding the KGSSHV board that I have built.

    I'm assuming that others would be similar depending on if they have

    bleeder resistors across the supplies filter capacitors.

    Also bleeddown time is governed by the cap's size (in mfd's) and the size of the bleeder resistor.

    I'm sure there is a mathematical formula that describes this, but I dont know it.

    The best way (for me) to be sure is to use a voltmeter to read the remaining voltage charge

    across the filter capactiors on the psu when switched off. For a given power supply, I use a stopwatch

    and check the caps multiple times until they bleed down to a "safe" voltage, say a couple of volts DC.

    Make sure that the thing is unplugged before starting and remember that the voltages encountered here are deadly!

    If you become part of the circuit, it can stop your heart, that is cause fibrillation that may result in death.

    My KGSSHV supply bleeds down to a safe level in about a minute.

    The specified bleeder resistors for this psu are 300K ohms to 400K ohm units.

    The intial voltage on each rail is 450 volts DC, so it has a total potential of double that, or 900 volts DC.

  10. I wouldn't personally pay extra for the same amp when the Japanese units can be changed to either 120 or 230V.

    Yes, but not everone is tech saavy as you are, and handy with a soldering iron.

    Then there is the issue with violating the warranty,

    that is if one is given when buying from a japanese vendor.

    Also the newer units are not "voltage switched" on the backside like some of the older units are. Right?

  11. Spritzer speaks the truth, power matters. (see post #62 above)

    Case in point, I have a low-end Stax setup.

    SR-202 Lambdas with a SRM-252II amplifier that has +/-280 volt output rails.

    The sound is incredible, but I have no headroom.

    The phones max out with SPL of ~85 to 90 dB depending on the source.

    I am currently building a KGSSHV with +/- 450 volt output rails.

    That should do the job (and then some). I really need MOAR POWER!

    I do plan on upgrading to the SR-507's in the near future as well.

    EDIT: I just saw your last post. I certainly do not claim to know

    everything as you do, but I do know that I need MOAR POWER!

    (and I want to keep it SS)

  12. The SRM-323 ouputs +/- 400 volts to the rails, what is the rating on the SRM-006t?

    EDIT: Found the answer. SRM-006t = +/- 300 volt rails.

    Regarding the "S" thing, you are referring to the older stuff, right?

    As of late, it seems the "S" suffix relates to 120volt mains input. (States?-for the U.S. market)

    While the "A" suffix denotes 100 volt mains for the Asian (japanese?)market.

    I could be wrong here, as I see conflicting vendor info on ebay.

    Would probably be smart to buy the amp from an established vendor in the USA

    to avoid the stepdown transformer hassles needed for a 100 volt mains unit.

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