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Author Topic: Ameritron AL-82 Loud Bang  (Read 11592 times)
W1QJ
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Posts: 1460




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« Reply #30 on: March 05, 2013, 05:01:35 AM »

Hi Bill.
Try to measure resistance on the output conector(must be few ohms)...when amp. is OFFLINE and DISCONECTED, but with extreme care(can be "safety choke" open, and then blocking caps discharging through output coax or conector or somewhere...

Load cap is spark gap maybe?? Wink
73 Kiko 9A4WY

I can see the safety in the pnoto, it looks OK, wouldn't hurt to put an ohm meter across the choke to check it.  Should be around 20 ohms.  Bill, try to measure across the safety choke to ground.  It is there under the big long coil.  It is a pi-wound choke.  Measure the resistance acroos it and see if you get about 20 ohms.  If it is open and you have a leaky blocking cap it could be.  But it looks pretty good to me in the photo, but you never know.  I doubt it is the spark gap on the plate tune cap.  Usually that noise is more of a PSSST noise than a bang.
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9A4WY
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« Reply #31 on: March 05, 2013, 12:01:53 PM »

Lou...
I mean if safety choke is open, first place to arc will be LOAD cap because it has smallest gap to GND.And I think it will be "bang"(2X500p blocking caps discharging to GND), because is pure DC, not pssst like RF arcing in plate cap.
Kristian 9A4WY
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W1QJ
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« Reply #32 on: March 05, 2013, 05:25:09 PM »

Lou...
I mean if safety choke is open, first place to arc will be LOAD cap because it has smallest gap to GND.And I think it will be "bang"(2X500p blocking caps discharging to GND), because is pure DC, not pssst like RF arcing in plate cap.
Kristian 9A4WY

Ok, that could be.  I wish he would put an ohm meter across that choke and see if it is opened.  Takes 30 seconds.
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N1DYX
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Posts: 39




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« Reply #33 on: March 05, 2013, 06:11:23 PM »

Sorry about the long delays in getting you information, I don't get home from work until late sometimes.  Thanks for your patience with me.

Anyway.......the choke looks good, measures about 23 ohms.  Also measured 23 ohms at the output connector.  Been looking this thing over with a 5X eye loupe and I sure don't see any physical signs, this is very strange.  Maybe it is something in the sheet metal buckling from the heat.  I ran across some chatter about bad transformers arcing after Peter Dahl stopped making them, but typically the unit would blow a fuse.

I'm gonna leave the cover off and turn the lights down as someone suggested and see if I see anything.

I appreciate all the feedback on this.

Here's some better pics, those others were pretty dark.  The tubes are not dark as they appear in the pictures it must be the flash.  I'll keep looking around.  Thanks

Bill

http://i29.photobucket.com/albums/c251/Bill75/DSC02326.jpg
http://i29.photobucket.com/albums/c251/Bill75/DSC02327.jpg
http://i29.photobucket.com/albums/c251/Bill75/DSC02328.jpg


« Last Edit: March 05, 2013, 06:24:40 PM by N1DYX » Logged
W1QJ
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« Reply #34 on: March 05, 2013, 11:21:10 PM »

Hi Bill, the thread is getting long, but maybe we went through this already?  Tell me, does the bangs only occur when the amp is transmitting?  Could the bang happen when the amp is on but not transmitting? Lou
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N1DYX
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« Reply #35 on: March 06, 2013, 04:10:02 AM »

Long for sure Lou!!  Yes it occurs even when not transmitting, it did it to me the other night. So that's suspicious a little.   Last night I made a couple of contacts with the cover off and had no problems but not very long transmissions.  I checked the inside of the cover very carefully for burn marks and saw nothing.  There's a small circuit board very high near the output connector that comes close to the cover but I didn't see much.  Some black on the edge of the board but I think it's just something inside the board laminate. 

I'm going to order some 220uF 500v caps today and in the mean time just watch more carefully, this is very strange.
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W1QJ
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« Reply #36 on: March 06, 2013, 05:17:44 AM »

That circuit board up near the coax connector doesn't have any HV around it.  Any bang you get when not transmitting has to be a HV arc.  It is more like a snapping sound.  I am surprised you don;t see a trace.  Maybe it is arcing up under the bottom of the filter cap board.  I know those amps have a steel type outer cover that I suppose could go BONG from expansion.
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N1DYX
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« Reply #37 on: March 06, 2013, 08:04:25 AM »

Not a snapping sound at all.  Heat on the cover certainly is possible, it's pretty loud.  Time will tell with this cover off and the lights down.
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N3QE
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« Reply #38 on: March 06, 2013, 10:33:24 AM »

Not a snapping sound at all.  Heat on the cover certainly is possible, it's pretty loud.  Time will tell with this cover off and the lights down.

Rather than go in and (as others have suggested) start swapping out capacitors or something... I still feel this must be the sheet metal flexing as unit heats up and cools down. If there's similar "bangs" as the unit cools down with AC power turned off that would be a clincher.

The pics you post, make this unit look pristine.

Of course we all know that Ameritron's competitors use a much better grade of sheet metal that is completely immune to thermal expansion and contraction. (Said tongue-in-cheek.)

I'm particularly befuddled how others have been convinced that a working amp obviously didn't have enough capacitors designed into it by the manufacturer, or that the working amp must have an opened plate choke. I mean, I've put new lytics in old equipment, and I've burnt out more than my share of plate chokes over the years. But this is a nearly new amp that's working just fine.
« Last Edit: March 06, 2013, 11:35:50 AM by N3QE » Logged
W8JX
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« Reply #39 on: March 06, 2013, 10:46:59 AM »

I think the bang is a sudden surge or increase in magnetic flux in transformer when there is short circuit and it flexes cabinet briefly.
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N1DYX
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Posts: 39




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« Reply #40 on: March 07, 2013, 06:19:49 AM »

Rather than go in and (as others have suggested) start swapping out capacitors or something... I still feel this must be the sheet metal flexing as unit heats up and cools down. If there's similar "bangs" as the unit cools down with AC power turned off that would be a clincher.

The pics you post, make this unit look pristine.

Of course we all know that Ameritron's competitors use a much better grade of sheet metal that is completely immune to thermal expansion and contraction. (Said tongue-in-cheek.)

I'm particularly befuddled how others have been convinced that a working amp obviously didn't have enough capacitors designed into it by the manufacturer, or that the working amp must have an opened plate choke. I mean, I've put new lytics in old equipment, and I've burnt out more than my share of plate chokes over the years. But this is a nearly new amp that's working just fine.



You make some good points.  I didn't run it last night but was thinking when I put the cover back on I'd leave the screws snug but not tight to allow the sheet metal to expand and contract without being constrained.  Kind of Odd that with all the Ameritron amps out there nobody else has seen this happen.  But you are correct, this thing has not seen much use and is very clean inside.

Trying to find those caps with screw mounts is next to impossible anyway, I thought I found them but they turned out to be snap mount.

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N3QE
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« Reply #41 on: March 07, 2013, 06:39:50 AM »

You make some good points.  I didn't run it last night but was thinking when I put the cover back on I'd leave the screws snug but not tight to allow the sheet metal to expand and contract without being constrained.  Kind of Odd that with all the Ameritron amps out there nobody else has seen this happen.  But you are correct, this thing has not seen much use and is very clean inside.

Well I have a different model Ameritron amp, and I know for sure as it heats up and cools down there's some sheet metal noises coming out. The thing that makes me 100 percent sure that it isn't an electrical thing, is that similar noises come out when cooling down with power removed and I know the bleeders work.

I did like your comment about the huge number of screws that hold on the cover :-). There's lots of sheet metal other than just the cover too.

Tim.
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K8AXW
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« Reply #42 on: March 07, 2013, 08:27:52 AM »

OK, let's examine this "sheet metal" thing.  It seems that the amp sheet metal is held together with a gazillion screws. 

I've seen and heard metal expansion and contraction with temperature and sometimes it can be loud.  However, it's been my observation that if sheet metal is fastened together with a lot of screws and expansion becomes a problem the metal buckles.  The screws keep it from actually moving from the anchor point so if it has to give it will form a buckle someplace.

So it seems to me that the next thing to check for is metal deformation after one of these "bangs."  If that can't be conveniently done then consider the next step.

Plan B would be to loosen a few of these screws and see what happens.  (Hey, I don't know....pick some)

Plan C, and one that is NOT recommended by anyone, even me, is to remove the amp from the case and operate it that way and see if you get these "bangs."  This is or could be a dangerous move but using proper precautions (Like paying very close attention to what you are doing, keeping family and pets out of the shack, etc.) this can be safely done.





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N1DYX
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Posts: 39




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« Reply #43 on: March 08, 2013, 06:55:16 AM »

I ran this thing for quite some time last night with the cover off and had no problems, everything was quiet so maybe it was the metal after all.  Man.........I feel a little stupid here for not thinking of doing that initially, it really didn't seem like all that noise could be coming from the metal expanding even though I did consider it at first.  I'll run it some more in the next few days to make sure before I secure the cover. 

You guys put allot of time into searching for answers and I appreciate the help very much.  Actually I learned some things here so it was time well spent for me.

Thank you

Bill
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W9KDX
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« Reply #44 on: March 08, 2013, 10:27:40 AM »

Slightly off topic, but I remember an old 8088 PC I worked on that only had problems when the cover was on.  Turned out the tightness of the cover flexed the motherboard and made one of the contacts intermitten.

Case issues can drive you crazy.
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Sam
W9KDX
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