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asdf32 posted:What are the voltages and currents involved and what's the accuracy required? The tube I'm working with right now requires 380V at ~1-5 uA, but I'd like this to go up higher so I can try it with other tubes or other designs that require different voltages. The parts I have (diodes and transistors) limit the maximum voltage I can handle to 1000V, and I'd probably put a safety margin in there, so let's say a range of ~100V to ~800V and a current of at most a few mA. Accuracy doesn't need to be too close since I plan to measure the output manually and adjust it so I figure I can probably compensate for any drift. Precision needs to be pretty good, since one of the main reasons I'm doing this is to measure where tubes start counting and things like that so I need the voltage to be pretty stable. Probably around +-5V stability (is this called ripple? I think this is called ripple but I'm not clear on that) asdf32 posted:The circuit shown would want some frequency compensation because tying the opamp output directly to the transistor hugely increases the loop gain. So specifically add a resistor between the 2.5V reference and the inverting input (1k-10k) and then add a cap between the opamp output and that (the inverting input). This is an integrator/pole/Type I Compensation. The 10k resistor and/or the transistor may dissipate a lot of power depending on the voltages and currents. Ah ok thanks. asdf32 posted:The shunt topology may be fine or it may be bad - it's the least efficient linear option and linear is already inefficient. It depends on the voltages and currents. I originally was playing around with that circuit first since it seemed simpler but I couldn't figure out how to make it variable, and also it seems like the zener would wind up dropping a few hundred volts across it which seems... bad... am I right about that?
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Apr 13, 2017 14:40
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Also last night I did some experiments with the CCFL driver and it seems like I can adjust the voltage fed to it to adjust its output voltage, and it's able to maintain that output voltage even if I put a load on it which is nice - I didn't really expect it to regulate so well outside its design range, it's just two transistors, two capacitors, an inductor and a transformer. Its output voltage scales very linearly with input voltage (like I charted it and the linear trendline has an R2 of 0.9993) but it's not quite precise enough to control only from that (if you ramp up the input voltage from 0 to 5V slowly it outputs something like exactly 600V, if you then go up above 5V and slowly wind it back down it outputs 620V, not sure what's going on there). Like I mentioned before I figure I'll get it "close" by controlling the input voltage and then bleed off the remaining difference with a linear regulator, so the regulator won't actually have to drop too much on its own.
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Apr 13, 2017 14:57
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ate all the Oreos posted:I originally was playing around with that circuit first since it seemed simpler but I couldn't figure out how to make it variable, and also it seems like the zener would wind up dropping a few hundred volts across it which seems... bad... am I right about that? The upper resistor (Rv here) is to limit current through the zener. If it is chosen appropriately it will naturally share the voltage.
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Apr 13, 2017 15:36
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Aurium posted:The upper resistor (Rv here) is to limit current through the zener. If it is chosen appropriately it will naturally share the voltage. Yeah I knew it's there to limit the current, though I didn't realize that zeners were okay with high voltages as long as the current is low. Or are you saying that the resistor and the zener will make a weird version of a voltage divider, with the zener dropping its zener voltage and the resistor dropping... everything else? Because I thought you'd need a higher Vbe than the output voltage to actually make current flow and turn the transistor on, meaning I'd need like a 400V zener (do they even make those?)
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Apr 13, 2017 15:45
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ate all the Oreos posted:Or are you saying that the resistor and the zener will make a weird version of a voltage divider, with the zener dropping its zener voltage and the resistor dropping... everything else? You got it. ate all the Oreos posted:Because I thought you'd need a higher Vbe than the output voltage to actually make current flow and turn the transistor on, meaning I'd need like a 400V zener (do they even make those?) Yes you would. You can series zener diodes as well to add thier values.
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Apr 13, 2017 18:00
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e: wrong thread
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Apr 13, 2017 19:40
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I've seen fixed-voltage radiation detector bias circuits that just use a bunch of stacked zeners for regulation after a pretty rough boosting stage. I've never built one like that myself though. In the G-M counter I built myself, I ripped off the boost topology from this circuit (boost converter followed by 7-stage Cockcroft-Walton multiplier) except with a microcontroller running the feedback logic instead of the analogue scheme. BattleMaster fucked around with this message at 02:59 on Apr 14, 2017 |
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Apr 14, 2017 02:57
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BattleMaster posted:I've seen fixed-voltage radiation detector bias circuits that just use a bunch of stacked zeners for regulation after a pretty rough boosting stage. I've never built one like that myself though. My first design used a transformer driven by a fixed oscillator that was turned on or off by a comparator. The secondary of the transformer was connected to a Cockcroft-Walton like that, but multiplying the output meant the manageable ripple coming from the transformer turned into something like 100-200V of ripple, and that was only a few multiplication stages. Admittedly if I actually used a micro to drive it instead of a fixed oscillator I could probably get it more stable but I have a bunch of extra CCFL drivers that output very nice clean stable voltages already... Anyway, thinking about the zener circuits people posted I went back and redesigned it as this:  The MOSFET part numbers are incorrect, I just picked ones LTSpice already had. The diodes are correct though. Output would be taken from right above R3, and R4 would be adjustable. This circuit seems reasonably stable in simulations, but it briefly spikes to the full input voltage before regulating when the simulation starts up, I'm not sure if that's actual behavior or if it's just the simulation being weird... e: I fiddled with it some more and realized the 10K resistor I was using to pull up the gate of the main MOSFET was low enough that it was the main thing burning off excess voltage rather than the MOSFET itself so I upped it an order of magnitude Shame Boy fucked around with this message at 15:13 on Apr 14, 2017 |
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Apr 14, 2017 14:15
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Hi guys. I am a newbie, please be gentle. I am trying to learn electronics starting from the very first principles. Working on RLC circuits and stuff, also because it lets me unrust my math. I have just started to work on transfer functions and I have realize there's one thing I simply don't understand. It's very basic, please bear with me.  I can work the math of these two circuits, find the formula for the cutoff frecuency relative to resistance and impedance etc.etc. The thing that I have no clue about is how do you define Vin and Vout according to the circuit? What's the logic behind it? Thanks in advance!
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Apr 14, 2017 18:44
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Dawncloack posted:Hi guys. I am a newbie, please be gentle. Vin is just whatever voltage you feed into it, e.g. from a battery or power supply. You'd typically have some kind of goal in mind with a circuit, so you'd know what you wanted to do with Vout, and Vin would be chosen based on the power available, goal of the project, etc. Basically, the sort of stuff you posted is the theory/science, but there's also the engineering aspect of "what do I have and what am I trying to do?" that comes when you actually attack a problem. I'm not sure how popular this view is, but nowadays I recommend people start with an Arduino, some pre-fab modules, and a project idea, then walk toward fundamental electronic theory as needed. The interoperability of COTS components today is really great. I work with a university group doing ocean mapping research, and we find ourselves slapping together existing modules more than doing fundamental EE stuff, because honestly, the world just doesn't need another power supply or amplifier circuit.
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Apr 14, 2017 18:57
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Yeah I guess it depends on what you want to get out of it. If you just want to build things that work I'd definitely focus on arduinos and modules and stuff. If you want the, uh, "fun" of trying to design each little part of a circuit and figuring out why your component melted or exploded this time go for fundamentals. Though even if you go fundamentals having a few arduinos is generally really helpful because you can use them as simple control stuff for experiments - I use mine to make arbitrary PWM square waves pretty often so I don't have to build an oscillator circuit just to test if an idea works.
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Apr 14, 2017 19:12
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I have not explained myself very well and I have just discovered that tinypic, too, is blocked in Turkey. Great. The thing is, I know what Vin and Vout are, what I don't understand is why in circuit one you have 1/jwC as Vout and not something else. In other words: what is the general logic that would allow me to take any filter composed of some capacitors, some resistors and some inductors and formulate ç Vout/Vin = (Z1 + Z2 + ... + Zn) / (Z'1 + Z'2 + ... + Z'N) for any circuit. That's what I don't know. About the starting with arduino and stuff, I agree with you. VVVVV thanks!! 
Dawncloack fucked around with this message at 08:14 on Apr 15, 2017 |
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Apr 14, 2017 22:40
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Dawncloack posted:I have not explained myself very well and I have just discovered that tinypic, too, is blocked in Turkey. Great. It's basically a voltage divider, with the capacitor forming the bottom half of the impedance. Vout is the same as the voltage over the cap, in that example.
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Apr 14, 2017 23:30
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Zero VGS posted:I was checking out some Tesla battery cables I have, and noticed they seem to be using some kind of cold-weld by just jamming the wiring straight on to the flat copper tabs: This is from a while back but it's been floating around in my head since then. In particular I was questioning whether or not a connection like that could be formed by crimping through the use of pressure alone. While browsing around the Molex site today I stumbled upon a page for Ultrasonically Welded Lug Cable Assemblies which looks very similar to the cable you have. A Google image search using these terms also produces images of similar looking cable assemblies.
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Apr 16, 2017 17:17
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I am replacing the capacitors on the HDMI daughterboard of my onkyo receiver. The guide I was using was for a slightly different model, and recommended purchasing 100uf 10v capacitors. After disassembling mine, the 100uf capacitors are all labeled 16v. Is it safe to assume that my 10v capacitors will not work, and I should order some 16v ones?
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Apr 16, 2017 18:01
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Yeah, the replacement capacitor needs to have the same or a higher voltage rating. If you put a higher voltage into a capacitor than it is designed for, it will leak or blow up.
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Apr 16, 2017 18:11
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It’s possible that the 16 V capacitors were specified for the reason of parts commonality and no other reason, but it’s not worth finding out. I suspect at least one of them is across a 12 V rail. I would probably replace them with 20 V caps anyway. There’s something wrong with the originals, after all.
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Apr 16, 2017 18:26
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so higher is ok? 20v is sold out on digikey, 25v would be just as good?
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Apr 16, 2017 18:31
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adorai posted:so higher is ok? 20v is sold out on digikey, 25v would be just as good? There are subtle differences in the properties of capacitors with different voltage ratings, but rarely does it matter with a capacitor as large as 100 µF.
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Apr 16, 2017 18:47
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Yeah when you're dealing with capacitors in the tens of uF or higher (the cylindrical ones, usually) you're generally talking about smoothing capacitors, and for those all that matters is "is the voltage equal to or higher than the old one so it doesn't explode" and "is the capacitance equal to or higher than the old one so it can do its job" Oh and "will it actually fit in the space", that's a big one I always wind up forgetting 
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Apr 16, 2017 19:17
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DethMarine21 posted:This is from a while back but it's been floating around in my head since then. In particular I was questioning whether or not a connection like that could be formed by crimping through the use of pressure alone. While browsing around the Molex site today I stumbled upon a page for Ultrasonically Welded Lug Cable Assemblies which looks very similar to the cable you have. A Google image search using these terms also produces images of similar looking cable assemblies. That's really cool, I went and found this boring guy giving a presentation about it that shows how it works: https://www.youtube.com/watch?v=yLGiY6Ehofo
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Apr 16, 2017 19:27
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Check out this comedy power cable that came with a cheap DC power brick: Not only is it a C13 plug with no corresponding ground, the wire is 20 AWG (max current rating 11A, meaning it may melt before the 15A breaker trips). EDIT: I cut it apart to salvage the wire for non-mains purposes, and I have never seen so little copper in so much insulation before. It's literally the same diameter as a breadboard pin.  EDIT: The jacket is even labeled as though it had 3 conductors! That's dedication. Stabby McDamage fucked around with this message at 03:33 on Apr 17, 2017 |
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Apr 17, 2017 03:27
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At least it doesn’t have a fake ground pin. Probably to save slightly on materials, but still.
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Apr 17, 2017 03:52
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Stabby McDamage posted:
Those breadboard wires are about the equivalent of a 22-gauge solid conductor, for comparison's sake. Not even the 20GA that you mentioned earlier.
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Apr 17, 2017 06:24
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Platystemon posted:At least it doesn’t have a fake ground pin. Perhaps it's made for a euro country, 230V would be used there so a smaller diameter wire would be fine, then instead of sourcing a new cable and everything they just replaced the plug.
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Apr 17, 2017 13:16
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His Divine Shadow posted:Perhaps it's made for a euro country, 230V would be used there so a smaller diameter wire would be fine, then instead of sourcing a new cable and everything they just replaced the plug. You're adorable
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Apr 17, 2017 18:14
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I looked it up and wire of that gauge is rated for less than 1 amp and this doesn't even count the fact that that kind of end plug requires a certain amperage capability to be supported by default (which is why it's that specific kind of plug that's used on computer power supplies and stuff like that)
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Apr 17, 2017 19:05
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ante posted:You're adorable It was just a guess and I am not at all an expert in electrics, heck I clicked on this thread by mistake. So could you elaborate your statement please so I can learn?
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Apr 18, 2017 06:23
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His Divine Shadow posted:It was just a guess and I am not at all an expert in electrics, heck I clicked on this thread by mistake. So could you elaborate your statement please so I can learn? My interpretation was “You are naïve for giving them the benefit of the doubt.”
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Apr 18, 2017 06:28
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His Divine Shadow posted:It was just a guess and I am not at all an expert in electrics, heck I clicked on this thread by mistake. So could you elaborate your statement please so I can learn? Yep, cheap Chinese* stuff cuts corners to save literally cents off a product in ways that make fiery doom a probability. Check out any youtube teardown of power supplies to see units only a wrap of scotch tape away from certain immolation. It's terrifying. *Expensive Chinese stuff is a different thing entirely, because everything is made there now
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Apr 18, 2017 06:57
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Tear downs of cheap chinese stuff will make you read the china thread in GBS and nod sagely. It is insane. The people who made it are insane. It's breathtaking how much effort has been put into half-assing stuff in such a way that makes it insanely dangerous. First, you'll find yourself exclaiming "surely this is actually more effort than just doing it properly". Eventually, you will stop and let the madness consume you. Expensive chinese stuff just meant a foreigner was there to start screaming incoherently when presented with a capacitor made of other, smaller capacitors.
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Apr 18, 2017 07:48
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You know I do read the GBS china thread... What does this say about me...
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Apr 18, 2017 11:31
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I got a bunch of these little MC34063EBN DC-DC converter control chips and I've used them a few times already and they seem to work fine, but this time I've actually tried going in and figuring out why each component has the value it does. I'm kinda stuck on this resistor: What's it doing there? It's only 0.33 ohms, is it for current sense? But the only terminal on the other side of it is VCC, is the chip somehow also using VCC for current sensing? Can I replace this resistor with something I have in less-weird-tiny values, like a 1 ohm one, as long as I don't need this thing to operate in super high currents? I guess I could also just parallel 3 1ohm resistors but I'm trying to save as much space on this board as possible. e: Looking at the datasheet more there's a formula for calculating it that's taken in reference to current so I guess it's current sense, that's the only other reference to it I can find though. I guess that formula answers my other questions about how much current it can handle at any given resistance, never mind. Shame Boy fucked around with this message at 14:25 on Apr 18, 2017 |
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Apr 18, 2017 14:16
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So my incredibly expensive minimum order of JST sockets came in... turns out the pins are too flimsy to solder into dongles without first mounting them to a PCB to stiffen up the pins. http://www.tlcelectronics.com/jst/S15B-PASK-2-LF-SN The pins are pitched exactly 2mm apart, but it seems like all common solder-type breadboards are 2.5mm... is there anywhere to get a bunch of 2mm solder breadboards? Failing that, I'm also seeing some GPIO 2mm-spaced pin headers online... is there any way to get those without the pins in them, so I can slide them over these pins to brace them? That seems like it would do the trick.
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Apr 18, 2017 23:46
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Like this? https://www.digikey.com/short/3wvmtj e: The price is silly on those, but that’s the idea, right? Seeed has these. Platystemon fucked around with this message at 00:08 on Apr 19, 2017 |
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Apr 19, 2017 00:02
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Zero VGS posted:So my incredibly expensive minimum order of JST sockets came in... turns out the pins are too flimsy to solder into dongles without first mounting them to a PCB to stiffen up the pins. Adaptor: https://oshpark.com/shared_projects/Er4MhUF9 Standardize, yo
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Apr 19, 2017 01:29
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ante posted:Adaptor: Those look perfect and the price is good... should I get the normal kind or the "2oz copper"? I could be running an upwards of 500ma through the traces. Edit: Found a calculator for it, seems like I'd be fine: http://circuitcalculator.com/wordpress/2006/01/31/pcb-trace-width-calculator/ Zero VGS fucked around with this message at 03:06 on Apr 19, 2017 |
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Apr 19, 2017 02:58
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Anyone know a bunch about audio circuits? I got some new headphones recently and am toying with the idea of building a DAC/amplifier for it. Are there any major parts of this that I'm missing? It seems pretty straightforward: - power filtering to clean up incoming USB power - USB codec chip to deal with the computer and output a stream of L/R audio samples over I2C - DACs to convert to analog - Buffer amp for drive current - Maybe another amplifier stage for volume control? Lots of off the shelf parts and layout seems like it'd be easy.
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Apr 19, 2017 06:40
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I'm just getting in to SMD stuff lately and pulled a bunch of old tantalum caps off of some old junk hardware and figured I'd use them in a circuit. Obviously the stripe means negative since that's what it means on diodes and every other capacitor ever right? Oh wait no it's drawing several amps and has begun to smoke guess not ¯\_(ツ)_/¯
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Apr 19, 2017 07:04
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You shouldn't use tantalum caps if you can avoid it anyway, they're a conflict resource.
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Apr 19, 2017 07:59
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