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Author Topic: Fuse blew on Amertitron 811  (Read 5220 times)
K4RVN
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« Reply #15 on: December 06, 2012, 05:12:11 PM »

DJ,
I think no one commented on the alc question to the 590. I don't think it would have helped you at all with the problem you reported. I don't connect my Icom 7200 to my three tube 811 amp based on I believe what I have read. I am of the opinion that the ALC on the 811 does little to protect it. I'm sure those who really know will comment to the contrary if they disagree. Also the inrush and 240V change won't hurt, but may not benefit you and probably were not necessary for this little amp. I still have an unbuilt soft start that I was going to put in mine, but read it was not necessary from someone who knows.
I am only mentioning these because I would not want someone to think they would benefit from what you did unless they investigated it first due to the cost. Of course you certainly did not hurt anything either by your choices. I plan to put glitch protection in my AL811 as I did on my AL80A which may protect the amp if the tubes go bang. Good luck and enjoy your amp.


Frank
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WX7G
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Posts: 6136




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« Reply #16 on: December 06, 2012, 05:35:42 PM »

It wasn't inrush current that caused a tube to arc, it was excessive drive causing the plate voltage to swing too high. ALC properly used might have saved the tube.

The 572B anodes will never get hot enough for the zirconium getter material to do its job of absorbing gas in the tube. This is why the 811A tube is a better choice with the amp running the tubes at less than 65 watts plate dissipation.

The 240 VAC inrush protection unit is not needed. Adding this and 572B tubes to this inexpensive amp is like trying to make a silk purse out of a sow's ear.
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W8JX
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« Reply #17 on: December 06, 2012, 06:02:00 PM »

The 572B anodes will never get hot enough for the zirconium getter material to do its job of absorbing gas in the tube. This is why the 811A tube is a better choice with the amp running the tubes at less than 65 watts plate dissipation.

I kinda disagree here. With the 3 tube amp I think it is a good idea because you can push tubes harder and warm them up some and you will not toast them with a full power tune up.  In a 4 tube 811 I think they are a bit of a waste as power supply is same as 3 tube model and has no reserve. While you need to keep plate current down below about 175ma per tube or 525 ma total for 3 tube or about 700 ma for 4 tube. The 572 has a safe limit of 275ma so running 3 tubes at 600 ma or more is not a problem for tubes.   Also the fan on a 811 amp is no up to cooling fully loaded 572's so they will warm up a bit when pushed.


The 240 VAC inrush protection unit is not needed. Adding this and 572B tubes to this inexpensive amp is like trying to make a silk purse out of a sow's ear.

I agree than a inrush protection is not needed but 572's will make it pretty bullet proof tube wise. Just run them hard. 
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N4CR
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« Reply #18 on: December 06, 2012, 06:49:30 PM »

You'll never get a 572B hot enough to getter in an 811 amp. So the end of life is more likely to come sooner than typical as the tube goes gassy.

Now, if you could cycle them through a real 572 amp once a year, they'd probably last forever.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
K4RVN
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Posts: 778




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« Reply #19 on: December 06, 2012, 07:51:43 PM »

Reply #16
Dave, the manual calls for max drive for full output of 70 watts and drive levels above 100 watts destructive. I have forgotten to turn my drive down a few times using my TenTec Omni 6 plus which has no ALC for the AL 811. I based my statement on what he said that he used 100 watts for 10 to 20 seconds talking  which was not above 100 watts maybe. You, of course, may be right but in my experience it was something else that made the tubes go bad.  The ALC is so slow cutting back the drive on the transceiver
 drive in the 811 amp that I can't imagine 20 seconds of 100 watts doing any harm for the amp. My 811s are over 3 1/2 years old now and doing well. I'm glad he suffered no  serious damage to the amp. It probably is a good idea to connect the ALC on this little amp to keep it clean on the output RF. 

Frank
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W8JX
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« Reply #20 on: December 07, 2012, 05:26:02 AM »

You'll never get a 572B hot enough to getter in an 811 amp. So the end of life is more likely to come sooner than typical as the tube goes gassy.

Now, if you could cycle them through a real 572 amp once a year, they'd probably last forever.

If you run it a reduced 811 levels yes but if you run the hard it should be fine. I have a old Dentron amp that has 4ea 572's that I run at 800 watts out 95+% of the time and tubes are still good 20 years later.
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N4CR
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« Reply #21 on: December 08, 2012, 09:50:35 AM »

If you run it a reduced 811 levels yes but if you run the hard it should be fine. I have a old Dentron amp that has 4ea 572's that I run at 800 watts out 95+% of the time and tubes are still good 20 years later.

That only proves that they didn't get gassy. It doesn't prove they were gettering. It could be that the seals on those tubes don't leak.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
W8JX
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Posts: 6088




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« Reply #22 on: December 08, 2012, 10:53:27 AM »

If you run it a reduced 811 levels yes but if you run the hard it should be fine. I have a old Dentron amp that has 4ea 572's that I run at 800 watts out 95+% of the time and tubes are still good 20 years later.

That only proves that they didn't get gassy. It doesn't prove they were gettering. It could be that the seals on those tubes don't leak.

Well at 800 out the tubes are dissipating at least 100 watts each and likely more and they glow dull red on long chats with compression so I know they are getting. Also a 811 supply cannot really make enough current to hurt 572's either.
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N4CR
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« Reply #23 on: December 08, 2012, 11:01:00 AM »

If you run it a reduced 811 levels yes but if you run the hard it should be fine. I have a old Dentron amp that has 4ea 572's that I run at 800 watts out 95+% of the time and tubes are still good 20 years later.

That only proves that they didn't get gassy. It doesn't prove they were gettering. It could be that the seals on those tubes don't leak.

Well at 800 out the tubes are dissipating at least 100 watts each and likely more and they glow dull red on long chats with compression so I know they are getting. Also a 811 supply cannot really make enough current to hurt 572's either.

The RCA rating of the 811A was 45 watts plate dissipation in CCS and 65 watts plate dissipation in ICAS. So, no, they are not dissipating 100 watts each. They are dissipating at most 25% of the 572B rating when pushed hard (CCS).
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
W8JX
Member

Posts: 6088




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« Reply #24 on: December 08, 2012, 05:16:04 PM »

If you run it a reduced 811 levels yes but if you run the hard it should be fine. I have a old Dentron amp that has 4ea 572's that I run at 800 watts out 95+% of the time and tubes are still good 20 years later.

That only proves that they didn't get gassy. It doesn't prove they were gettering. It could be that the seals on those tubes don't leak.

Well at 800 out the tubes are dissipating at least 100 watts each and likely more and they glow dull red on long chats with compression so I know they are getting. Also a 811 supply cannot really make enough current to hurt 572's either.

The RCA rating of the 811A was 45 watts plate dissipation in CCS and 65 watts plate dissipation in ICAS. So, no, they are not dissipating 100 watts each. They are dissipating at most 25% of the 572B rating when pushed hard (CCS).


If this was the case there would not be so many 811 melt downs or tube failures. To run a 4 tube 811 amp at 800 watts out you are exceeding tubes ratings plain and simple. When you tune you can easily metal down a 811 if you are not careful. Not a problem with a 572 in it
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VA3KBC
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« Reply #25 on: December 20, 2012, 05:43:55 AM »

Taylor 572B's installed and everything works great.
For some reason it didn't like Bill's Icom when we tried it out after installing the tubes, but works great with my TS590.
No problem getting 600 watts.
Relay and ALC cable will make sure I don't over drive things as well.
I run 500 max and this amp/572B's will last me a long time now...hopefully. Smiley
Thanks Bill, VE3WIG.
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