Author Topic: Full wave CW Multiplier possible punch through  (Read 887 times)

Offline FonziDaytona

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Full wave CW Multiplier possible punch through
« on: July 13, 2022, 05:39:47 PM »
Hi everyone,

I recently built a full wave CW multiplier (6 stages) and a hand wound ferrite transformer (20kHz) to power it. I used 6kV 47nF wima FKP1 capacitors (2 in series per stage). The voltage rating should be 72kV if I assume 100% voltage rating of the capacitors. This is running under oil.

So far, I’ve pushed it to -66kV and 11mA to power a fusor. This shouldn’t be stressing it, but I can hear the sounds of popping coming from the multiplier. I’m afraid that I’m hearing the capacitors having punch through events. Each time I hear popping noises, I see my voltage dip. I’ve opened up the multiplier a few times to test the capacitors and see they are still reading within spec…

Anyone here with experience? Are these 6kV capacitors just not rated for 6kV or do I have something fundamentally wrong?

Here are a few pictures of the new, two coil center tapped transformer, the completed multiplier, and the multiplier under construction.

Edit: Forgot to add details of the transformer for completeness:

506 turns per coil and I am now using a 7 turn primary fed by a car amp and a signal generator. Primary voltage is 55vrms. My output calculation going into the multiplier is 506/7*55*1.414 = 5622v. This should be putting around 11kV across each stage which is under the 12kV rating. This is why I’m confused by what sounds like capacitor failure. I’m unable to see through the multiplier container, so am assuming it’s not from arcing between stages/wire/diodes etc.

-Matt



« Last Edit: July 13, 2022, 06:25:56 PM by FonziDaytona »

Offline MRMILSTAR

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Re: Full wave CW Multiplier possible punch through
« Reply #1 on: July 13, 2022, 09:16:41 PM »
Computing the exact output voltage of your flyback transformer is tricky. I would actually measure its output because it may be more than you think. I made a special test setup just to measure the output voltage of my flyback transformers for my CW voltage multiplier. Its fairly simple to build and just requires four fast HV diodes, a smoothing capacitor, and a COTS HV DC meter. You can see how I built this here.
https://highvoltageforum.net/index.php?topic=1524.0
« Last Edit: July 13, 2022, 09:24:38 PM by MRMILSTAR »
Steve White
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Offline FonziDaytona

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Re: Full wave CW Multiplier possible punch through
« Reply #2 on: July 13, 2022, 11:37:28 PM »
Hi Steve,

I was thinking that there might be some resonant rise occurring and taking me up higher than I calculated. That would be disappointing to not see a correspondingly higher DC voltage though…

How accurate would a Fluke 40kV probe be at “high” frequency AC? I have a 40kV and a 6kV probe to go with my fluke 179 (claims accurate frequency measurements to 100khz).

-Matt

Offline klugesmith

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Re: Full wave CW Multiplier possible punch through
« Reply #3 on: July 14, 2022, 03:55:08 AM »
Nice work there.  Can you operate with the lid off so you can see the oil surface?  Not only to look for sparks in the dark, but to see if the oil circulates rapidly when high voltage is on.
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Why do you care about high frequency AC?  The C-W multiplier develops DC, without much ripple if there's no load current except for the kilovoltmeter.

In professional EE work, capacitors are usually operated at significantly less then their datasheet rated voltage.  Conversely, HV amateurs and coilers often compare notes about abusing components by running at higher than rated voltage.   
« Last Edit: July 14, 2022, 04:06:14 AM by klugesmith »

Offline MRMILSTAR

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Re: Full wave CW Multiplier possible punch through
« Reply #4 on: July 14, 2022, 05:40:05 AM »
Hi Steve,

I was thinking that there might be some resonant rise occurring and taking me up higher than I calculated. That would be disappointing to not see a correspondingly higher DC voltage though…

How accurate would a Fluke 40kV probe be at “high” frequency AC? I have a 40kV and a 6kV probe to go with my fluke 179 (claims accurate frequency measurements to 100khz).

-Matt
If you first full-wave rectify and smooth the AC output of the flyback transformer then you can use your Fluke DC meter with good accuracy because you will be measuring DC instead of AC. This is what I did with my special measurement apparatus. Be sure and have the multiplier stack connected so that its full load impedance is accounted for in the measurement. The measurement is then the peak AC output voltage of the flyback transformer. This number can then guide you as to how close you are to the maximum voltage rating of your capacitors.

If you truly have a 40 KV AC meter accurate to 100 KHz then it should be able to measure the output of the flyback transformer directly.
« Last Edit: July 14, 2022, 05:48:32 AM by MRMILSTAR »
Steve White
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Offline FonziDaytona

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Re: Full wave CW Multiplier possible punch through
« Reply #5 on: July 14, 2022, 03:29:31 PM »
I’ll see about operating with the lid off, it’ll be a bit of a pain since I have very tight tolerances. If I see circulating oil, what would be my next steps?

If I energize the CW and keep it unloaded, could I use that DC measurement to back calculate what my AC voltage is at the transformer?

-Matt

Offline MRMILSTAR

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Re: Full wave CW Multiplier possible punch through
« Reply #6 on: July 14, 2022, 04:00:55 PM »
There are many losses in a CW multiplier that cause the output to deviate from the ideal. That is one problem in trying to back-calculate the flyback transformer output. The other problem is accurately measuring the output of the CW voltage multiplier.

The only accurate way to determine the loaded output of your flyback transformer is to measure it. One way is to use the method that I described earlier.
Steve White
Cedar Rapids, Iowa
Retired electrical engineer

Offline FonziDaytona

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Re: Full wave CW Multiplier possible punch through
« Reply #7 on: July 14, 2022, 09:39:43 PM »
I’ve got a few hv diodes and capacitors left over so should be able to throw something together for measuring the transformer voltage.

When you mention hooking up the multiplier to this, would that mean trying the AC inputs of the bridge rectifier (smoothed) to the AC inputs of the multiplier and then measuring voltage from the bridge rectifier while loading the multiplier?

-Matt

Offline MRMILSTAR

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Re: Full wave CW Multiplier possible punch through
« Reply #8 on: July 14, 2022, 10:52:58 PM »
The CW multiplier is configured as is usual. You then just connect the full-wave bridge rectifier across the output of the flyback transformer. You don't modify the multiplier circuitry in any way.
Steve White
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Retired electrical engineer

Offline FonziDaytona

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Re: Full wave CW Multiplier possible punch through
« Reply #9 on: July 15, 2022, 12:24:10 AM »
Steve,

You’ll have to excuse my ignorance as it’s been a long time since my college EE days:

I’m using a center tap (grounded) transformer. Do I need a bridge rectified configuration or just two diode full wave configuration? If bridge rectified, can I just ground the positive (my CW is negative output) output of the bridge rectifier?

-Matt

Offline klugesmith

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Re: Full wave CW Multiplier possible punch through
« Reply #10 on: July 15, 2022, 01:18:05 AM »
When full wave bridge rectifier goes before the voltage divider, you need fast HV diodes, but voltage divider R's are not exposed to high frequency.

You can use fast low voltage diodes, if bridge rectifier goes between the high-R and low-R elements of voltage divider.
Then the high frequency behavior of high-R element (from parasitic L and C) can matter.
Measuring output of a transformer like you showed us, I would be OK with knowing average rectified voltage (instead of peak or RMS).


I used that extensively for measuring line frequency NST's with center tapped secondaries.
Kilovoltmeter unit is compact & typically sits on a big sheet of plastic foam for HV isolation.
 
« Last Edit: July 15, 2022, 01:32:27 AM by klugesmith »

Offline klugesmith

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Re: Full wave CW Multiplier possible punch through
« Reply #11 on: July 15, 2022, 01:28:38 AM »
>>If bridge rectified, can I just ground the positive (my CW is negative output) output of the bridge rectifier?

Draw schematic of CW _and_ measuring rectifer both connected to transformer output,
including both ground connections.  Answer should be obvious.

Offline davekni

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Re: Full wave CW Multiplier possible punch through
« Reply #12 on: July 15, 2022, 05:08:43 AM »
Quote
I recently built a full wave CW multiplier (6 stages) and a hand wound ferrite transformer (20kHz) to power it. I used 6kV 47nF wima FKP1 capacitors (2 in series per stage). The voltage rating should be 72kV if I assume 100% voltage rating of the capacitors. This is running under oil.

So far, I’ve pushed it to -66kV and 11mA to power a fusor. This shouldn’t be stressing it, but I can hear the sounds of popping coming from the multiplier. I’m afraid that I’m hearing the capacitors having punch through events. Each time I hear popping noises, I see my voltage dip. I’ve opened up the multiplier a few times to test the capacitors and see they are still reading within spec…

Anyone here with experience? Are these 6kV capacitors just not rated for 6kV or do I have something fundamentally wrong?
I have experience with 22nF 6kV WIMA FKP1 caps.  No issue with DC.  Not great for AC.
The picture shows no resistors across caps.  Especially for DC, series-connected caps need resistors across each cap to keep voltage split evenly.  Otherwise leakage current (to case or whatever) slowly unbalances voltage.  One 6kV cap of each pair will have lower voltage and the other higher.  My guess is that you are hearing snaps when a cap arcs internally, very-slightly reducing its capacitance, and re-balancing voltage.  Of course, resistors need to be rated for 6kV or more.  (These FKP1 caps do degrade very slowly, loosing only a tiny bit of capacitance with each over-voltage event.  I've used them to 8.5kV short-term in my small Marx generator.  These failure events might even slowly resolve themselves.  After many such failures, film capacitors develop DC leakage current.  Such current will be in the direction to better balance voltages.)

Quote
If you first full-wave rectify and smooth the AC output of the transformer then you can use your Fluke DC meter with good accuracy because you will be measuring DC instead of AC.
If using a full-wave bridge for rectification, wire it across the entire secondary (both windings).  If wired across only one winding, the DC bridge output will have a large AC common-mode component that can confuse meters etc.  If measuring a single winding, use a full-wave voltage multiplier instead of a bridge.  Resulting DC will be the same as a bridge across both windings.

Quote
If I energize the CW and keep it unloaded, could I use that DC measurement to back calculate what my AC voltage is at the transformer?
Transformer output will change with loading due to leakage inductance and winding resistance and AC input source impedance.  Measuring unloaded is not accurate for loaded output.  Probably a good upper-bound for loaded transformer voltage, and a good measure of unloaded transformer output voltage.  Given your multiplier capacitance and operating frequency, I suspect it will drop less than 1% with loading due to capacitor ripple alone.  Transformer output impedance will be much more significant.  Don't know about multiplier diode forward voltage drop.

Quote
I’m using a center tap (grounded) transformer. Do I need a bridge rectified configuration or just two diode full wave configuration? If bridge rectified, can I just ground the positive (my CW is negative output) output of the bridge rectifier?
Good point.  Your transformer and load are close enough to symmetric that two-diode full-wave rectification should be sufficient.  (I think current waveforms into multiplier are slightly different on positive and negative input voltage peaks, but probably not enough to matter in your measurements.  You could reverse the two diodes and see if the voltage reading has the same magnitude and opposite polarity if you want to be certain.  Won't matter if measuring unloaded voltage.)

One more note:  The two bottom outside caps within the multiplier see only half voltage (peak, not peak-to-peak).  There is no need to use two series caps for those.  Multiplier voltage droop will be a bit less with 47nF instead of 47nF/2 for those two initial capacitors.
« Last Edit: July 15, 2022, 06:14:39 PM by davekni »
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Re: Full wave CW Multiplier possible punch through
« Reply #13 on: July 15, 2022, 05:44:03 AM »
Perhaps this will clarify things. Connect the full-wave bridge to the 2 inputs of your multiplier stack. Be sure and use fast diodes.
Steve White
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Offline FonziDaytona

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Re: Full wave CW Multiplier possible punch through
« Reply #14 on: July 15, 2022, 06:46:47 PM »
I didn’t even think of the balancing being the issue, but might be.

I’ve noticed that as I push for higher voltages, there will be pops, and then it’ll get better. If I push a little higher, same routine.

It used to pop around 48kV and then I could get up into the 50’s before pops were heard. Maybe it’s “breaking in” the hard way?

I have managed to kill a few of these in a previous 4 stage multiplier, half wave, but I was also over volting them pretty badly. I’d hear A LOT of popping and I could see the return wire jumping around…

If I were to add some balancing resistors, what would you recommend for these 6kV wima capacitors?

Thanks!
Matt

Offline davekni

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Re: Full wave CW Multiplier possible punch through
« Reply #15 on: July 16, 2022, 01:44:09 AM »
Quote
It used to pop around 48kV and then I could get up into the 50’s before pops were heard. Maybe it’s “breaking in” the hard way?
I suspect so.  I don't have much experience with oil insulation.  Klugesmith pointed out oil stirring.  That implies significant charge transfer, though I don't know how much.  Likely enough to be problematic.

Quote
If I were to add some balancing resistors, what would you recommend for these 6kV wima capacitors?
Vishay's VR68 family is good, 10kV rated.  I purchased a box of 68meg (no relation to the "68" in part family number) for such purposes.  Since under oil, you might get away with VR37 33meg (the highest value offered), even though 6kV would be twice VR37's 0.5W power rating.
David Knierim

Offline FonziDaytona

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Re: Full wave CW Multiplier possible punch through
« Reply #16 on: July 16, 2022, 07:23:46 PM »
I’ll get some VR68, 68Mohm resistors on order…

While I haven’t yet constructed a full wave rectifier for measuring the transformer voltage, I did try out my fluke 40kV probe and found something interesting (to me anyways). I am measuring high side of coil 1 to center tap connection (probe tip to high side and probe ground clip to center tap) and then comparing to high side of coil 2 to center tap position. Coil 1 is 10x higher than coil 2. I expected them to be both the same.

I’m definitely a novice, but would think this is not good for a multiplier.

Here is how I have my two coils oriented:


-Matt
« Last Edit: July 16, 2022, 07:26:08 PM by FonziDaytona »

Offline davekni

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Re: Full wave CW Multiplier possible punch through
« Reply #17 on: July 16, 2022, 07:57:45 PM »
Quote
Coil 1 is 10x higher than coil 2. I expected them to be both the same.
Yes, your expectation is reasonable.  If this Fluke probe is designed for line-frequency use, it may be damaged by 20kHz.  Scope probes have reduced voltage handling capability as frequency increases.  Same is likely true of meter probes.

Is this measurement of transformer alone or while connected to multiplier?  Unless your probe fried between the two measurements, it sounds like there is a failure within either one winding or within multiplier (shorting one winding).

Quote
I’m definitely a novice, but would think this is not good for a multiplier.
Multiplier will operate when driven by only one side.  All the multipliers I've built have only a single AC input (two stacks of capacitors rather than three).  Running both sides will reduce output ripple and voltage droop under load.
David Knierim

Offline FonziDaytona

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Re: Full wave CW Multiplier possible punch through
« Reply #18 on: July 16, 2022, 08:44:52 PM »
I tried connected to multiplier (no load) and disconnected from multiplier. Both instances gave large differences.

I just tried out my 6kV probe and found that both sides are pretty close to each other, so maybe the 40kV probe is faulty? I’ll try it out with DC later…

Interestingly enough, the 6kV probe was only 15% off from what I calculated the voltage to be…

Edit: Should clarify that these aren’t scope probes, they are DMM probes made by Fluke. They are just some high voltage resistors inside.

-Matt

« Last Edit: July 16, 2022, 08:54:46 PM by FonziDaytona »

Offline FonziDaytona

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Re: Full wave CW Multiplier possible punch through
« Reply #19 on: July 28, 2022, 01:40:37 AM »
Update: I installed all of the balancing resistors and am still having the popping issues. I notice that this is only happening under load. If I take it up to 68kV and leave it unloaded, no popping noises. As soon as I begin to draw some current, popping.

-Matt

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Re: Full wave CW Multiplier possible punch through
« Reply #19 on: July 28, 2022, 01:40:37 AM »

 


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July 28, 2022, 03:35:48 AM
post DRSSTC from Aliexpress
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ItsChloeUwU
July 28, 2022, 03:27:40 AM
post Re: Looking for a good schematic to follow for my first audio sstc coil :3
[Solid State Tesla Coils (SSTC)]
ItsChloeUwU
July 28, 2022, 03:19:17 AM
post Re: A big-ish diy xformer
[Transformer (Ferrite Core)]
oneKone
July 28, 2022, 03:04:48 AM
post Re: A big-ish diy xformer
[Transformer (Ferrite Core)]
oneKone
July 28, 2022, 03:00:59 AM
post Re: Full wave CW Multiplier possible punch through
[Voltage Multipliers]
FonziDaytona
July 28, 2022, 01:40:37 AM
post Re: A big-ish diy xformer
[Transformer (Ferrite Core)]
FonziDaytona
July 28, 2022, 01:18:31 AM
post gdt is giving a perfect signal and good current but the mosfet are not swithing
[Solid State Tesla Coils (SSTC)]
alex
July 27, 2022, 11:21:13 PM
post Help with TC schematic
[Solid State Tesla Coils (SSTC)]
MoonMatthew
July 27, 2022, 07:01:22 PM
post Re: Secondary former material
[Spark Gap Tesla Coils (SGTC)]
55#sofcopper
July 27, 2022, 06:15:44 PM
post Re: Gate waveform question
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Mads Barnkob
July 27, 2022, 02:17:25 PM
post Re: Looking for a good schematic to follow for my first audio sstc coil :3
[Solid State Tesla Coils (SSTC)]
Mads Barnkob
July 27, 2022, 02:10:20 PM
post Re: Secondary former material
[Spark Gap Tesla Coils (SGTC)]
Mads Barnkob
July 27, 2022, 02:07:24 PM
post Re: A big-ish diy xformer
[Transformer (Ferrite Core)]
Mads Barnkob
July 27, 2022, 02:01:29 PM
post Secondary former material
[Spark Gap Tesla Coils (SGTC)]
55#sofcopper
July 27, 2022, 08:06:36 AM
post Re: Looking for a good schematic to follow for my first audio sstc coil :3
[Solid State Tesla Coils (SSTC)]
AstRii
July 27, 2022, 05:40:14 AM
post Smoke detector carrying plutonium
[General Chat]
farleymartinez
July 27, 2022, 04:37:44 AM
post Re: Looking for a good schematic to follow for my first audio sstc coil :3
[Solid State Tesla Coils (SSTC)]
ItsChloeUwU
July 26, 2022, 09:45:49 PM
post Re: Looking for a good schematic to follow for my first audio sstc coil :3
[Solid State Tesla Coils (SSTC)]
ItsChloeUwU
July 26, 2022, 09:45:37 PM
post Re: Looking for a good schematic to follow for my first audio sstc coil :3
[Solid State Tesla Coils (SSTC)]
ItsChloeUwU
July 26, 2022, 09:44:28 PM
post Re: Looking for a good schematic to follow for my first audio sstc coil :3
[Solid State Tesla Coils (SSTC)]
ZakW
July 26, 2022, 06:00:18 PM
post Re: Looking for a good schematic to follow for my first audio sstc coil :3
[Solid State Tesla Coils (SSTC)]
AstRii
July 26, 2022, 04:22:27 PM
post Re: Looking for a good schematic to follow for my first audio sstc coil :3
[Solid State Tesla Coils (SSTC)]
ItsChloeUwU
July 26, 2022, 04:15:51 PM
post Re: Looking for a good schematic to follow for my first audio sstc coil :3
[Solid State Tesla Coils (SSTC)]
ItsChloeUwU
July 26, 2022, 04:11:27 PM
post Re: Gate waveform question
[Dual Resonant Solid State Tesla coils (DRSSTC)]
flyingperson23
July 26, 2022, 03:57:42 PM
post Re: Looking for a good schematic to follow for my first audio sstc coil :3
[Solid State Tesla Coils (SSTC)]
AstRii
July 26, 2022, 08:59:32 AM
post Re: Gate waveform question
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Mike
July 26, 2022, 06:08:01 AM
post Re: A big-ish diy xformer
[Transformer (Ferrite Core)]
oneKone
July 26, 2022, 05:51:33 AM
post Re: A big-ish diy xformer
[Transformer (Ferrite Core)]
davekni
July 26, 2022, 04:41:00 AM
post Re: Gate waveform question
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
July 26, 2022, 04:24:36 AM
post A big-ish diy xformer
[Transformer (Ferrite Core)]
oneKone
July 26, 2022, 04:10:58 AM
post Re: 60 hz hum in KLH receiver
[Electronic Circuits]
davekni
July 26, 2022, 03:48:23 AM
post Re: Gate waveform question
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Mike
July 26, 2022, 03:10:06 AM
post Re: Gate waveform question
[Dual Resonant Solid State Tesla coils (DRSSTC)]
flyingperson23
July 26, 2022, 01:46:12 AM
post Re: 60 hz hum in KLH receiver
[Electronic Circuits]
petespaco
July 26, 2022, 12:16:12 AM
post Re: 60 hz hum in KLH receiver
[Electronic Circuits]
Twospoons
July 25, 2022, 11:55:33 PM
post 60 hz hum in KLH receiver
[Electronic Circuits]
MRMILSTAR
July 25, 2022, 10:20:45 PM
post Re: Gate waveform question
[Dual Resonant Solid State Tesla coils (DRSSTC)]
flyingperson23
July 25, 2022, 05:18:07 PM
post Looking for a good schematic to follow for my first audio sstc coil :3
[Solid State Tesla Coils (SSTC)]
ItsChloeUwU
July 25, 2022, 03:23:13 PM
post Total Pro Tp40 Servis Manuel Gerekli
[Spark Gap Tesla Coils (SGTC)]
Cem888
July 24, 2022, 10:16:27 PM
post HBK-2216 power supply
[Electronic Circuits]
costas_p
July 24, 2022, 12:15:54 PM
post Re: Racing arcs on secondary
[Spark Gap Tesla Coils (SGTC)]
MRMILSTAR
July 24, 2022, 05:06:32 AM
post Re: Gate waveform question
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
July 24, 2022, 04:15:16 AM

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