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Author Topic: Ameritron AL 811H - loud snapping sound  (Read 5078 times)
AE6YB
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« on: October 17, 2015, 01:29:40 PM »

I have an 8 year old AL811H, purchased new that has just recently started making a loud snap periodically, about every couple of minutes or so. I don't have any idea what could be causing this. It is clean inside, no dust and has been only used in a clean environment and has never been driven with more than 60 watts. Any ideas??

 Thanks, Will, AE6YB
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N4ATS
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« Reply #1 on: October 17, 2015, 01:55:22 PM »

Typical , replace ALL the bleeder resistors and the HV Caps
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G3RZP
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« Reply #2 on: October 18, 2015, 12:36:18 AM »

'Dying' electrolytics can do this even when the equalising resistors are OK. But as N4ATS says, replace the capacitors and the resistors.
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W1QJ
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« Reply #3 on: October 18, 2015, 03:46:36 AM »

Agreed
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N0XWR
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« Reply #4 on: October 18, 2015, 04:05:20 AM »

I have an AL811 doing the exact same thing. Would a 100k 5 watt metal film resistor substitute for the stock 50k 7 watt bleeder?  Thanks. 73 Jerry N0XWR
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N8CBX
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« Reply #5 on: October 18, 2015, 05:56:04 AM »

Were is the arcing happening with the caps? Is it internal?
Jan N8CBX
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Dayton Ohio - The Birthplace of Aviation
W1QJ
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« Reply #6 on: October 18, 2015, 06:44:33 AM »

I have an AL811 doing the exact same thing. Would a 100k 5 watt metal film resistor substitute for the stock 50k 7 watt bleeder?  Thanks. 73 Jerry N0XWR

yes, the only problem is that it takes longer for the HV to bleed down, other than that they are used all the time.  Even 3 watts is plenty.
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AD4U
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« Reply #7 on: October 18, 2015, 07:21:36 AM »

I also must ask, "What is going on and why all the failures"? I thought new electrolytic caps were supposed to be better than the old ones. Why don't they last? Maybe the new caps being much smaller physically has something to do with their short life.

I have a SB-200 that I built in 1970 that is still running the original 45 year old HV caps. I have a Collins 30L1 that is still running the original 50 year old caps.

Dick AD4U
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W1QJ
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« Reply #8 on: October 18, 2015, 08:03:14 AM »

Ameritron has  tendency to use the minimum number of filter caps in their power supplies.  That puts the voltage across each cap at about 90% of full value.  A larger gap in voltage at maximum would make the caps last much longer.  This is a problem with all their amps.  The big ones AL-82,1200,1500 are as bad.  I usually add two more caps for a total of 10 and that solves the problem.
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WA7PRC
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« Reply #9 on: October 18, 2015, 10:12:38 AM »

Ameritron has  tendency to use the minimum number of filter caps in their power supplies.  That puts the voltage across each cap at about 90% of full value.  A larger gap in voltage at maximum would make the caps last much longer.  This is a problem with all their amps.  The big ones AL-82,1200,1500 are as bad.  I usually add two more caps for a total of 10 and that solves the problem.
Electrolytic capacitors hate heat. More capacitors in series reduces the AC current through each capacitor, reducing the heating of each capacitor. That increases capacitor life. Another way to increase the life is to use capacitors that have a higher heat range and/or greater ripple current rating.

vy 73 es gl,
Bryan WA7PRC
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G3RZP
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« Reply #10 on: October 18, 2015, 10:13:42 AM »

One problem that was found years ago with electrolytics - and may well not apply with today's devices - is that they get a 'memory'. A 450 volt cap run at 350 volts needs proper reforming before it can stand 450 again.

The arc that gives rise to 'snap' sound has been, in all the capacitors in which I have observed it, been internal. I've seen the effect appear in capacitors from the 1970s and later, while I have parts from the 1950s and 60s still working well in the original equipment at 350 - 400 volts.

Quote
Ameritron has  tendency to use the minimum number of filter caps in their power supplies.  That puts the voltage across each cap at about 90% of full value
.

Doesn't leave much headroom for mains voltage excursions.......but does save money.
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W1BR
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« Reply #11 on: October 18, 2015, 11:15:34 AM »


Electrolytic capacitors hate heat. More capacitors in series reduces the AC current through each capacitor, reducing the heating of each capacitor. That increases capacitor life. Another way to increase the life is to use capacitors that have a higher heat range and/or greater ripple current rating.

vy 73 es gl,
Bryan WA7PRC

How does that work?  The caps are in series. Current is constant in a series circuit, regardless.  ESR voltage drop and ripple current is what generates heat.

pete
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AE6YB
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« Reply #12 on: October 18, 2015, 04:35:04 PM »

Thanks for all of the comments. I have located the noise. Any ideas on this....it's a ferrite bead. About every 2 to 3 minutes it moves and makes a snap sound. Should it be moving and is there anything I can do to stop it from moving?
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WA7PRC
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« Reply #13 on: October 18, 2015, 04:35:29 PM »

As in any series circuit, increased total ESR = decreased ripple current. The same voltage divided across more capacitors x decreased ripple current = less dissipation (and less heat).
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WA7PRC
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« Reply #14 on: October 18, 2015, 04:37:00 PM »

Thanks for all of the comments. I have located the noise. Any ideas on this....it's a ferrite bead. About every 2 to 3 minutes it moves and makes a snap sound. Should it be moving and is there anything I can do to stop it from moving?
It shouldn't move. A piece of tape or a Nylon cable tie(s) will hold it in place.
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