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Author Topic: AL-811H Lost Plate Current  (Read 12857 times)
WY7CHY
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Posts: 933




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« Reply #15 on: August 12, 2016, 09:58:16 AM »

Thanks for the reply W8JX

I'm not quite sure however of one of your answers. The AL-811H is rated as an 800w SSB/PEP amplifier. The NON-H model is rated at 600w. And with a pretty accurate PEP meter, I have been getting close to the 800w out, with about 65-70w input.

So why are you saying that 800w is exceeding the ratings by a whole lot? Why would they rate the amp at 800w if you're saying that isn't correct? Thanks. Mike.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
WY7CHY
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Posts: 933




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« Reply #16 on: August 12, 2016, 09:59:29 AM »

Back on topic.

As I asked previously, IF a tube had shorted, and that caused the Plate Choke to pop, is it possible that the tube is STILL SHORTED, and if I replace the plate choke, the tube could blow the new choke? Is there a way to somewhat test the 4 tubes; other than all 4 do light up?

Thanks. Mike

As I stated earlier use a ohm meter to check plate to grid and plate to filament in each tube. 

Should BOTH Plate to Grid....... and Plate to Filament...... be OPENS?

Thanks. Mike
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
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Posts: 13268




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« Reply #17 on: August 12, 2016, 10:00:14 AM »

Back on topic.

As I asked previously, IF a tube had shorted, and that caused the Plate Choke to pop, is it possible that the tube is STILL SHORTED, and if I replace the plate choke, the tube could blow the new choke? Is there a way to somewhat test the 4 tubes; other than all 4 do light up?

Thanks. Mike

As I stated earlier use a ohm meter to check plate to grid and plate to filament in each tube. 

Should BOTH Plate to Grid....... and Plate to Filament...... be OPENS?

Thanks. Mike

Yes
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Ham since 1969....  Old School 20wpm REAL Extra Class..
WY7CHY
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Posts: 933




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« Reply #18 on: August 12, 2016, 10:07:37 AM »

w8jx. While you're online, what about the previous question about the 800w PEP rated for the al-811H. Why do you say that is exceeding? Did you mean the 3 tube AL-811 instead of the AL-811H?
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
Member

Posts: 13268




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« Reply #19 on: August 12, 2016, 10:11:37 AM »


I'm not quite sure however of one of your answers. The AL-811H is rated as an 800w SSB/PEP amplifier. The NON-H model is rated at 600w. And with a pretty accurate PEP meter, I have been getting close to the 800w out, with about 65-70w input.

So why are you saying that 800w is exceeding the ratings by a whole lot? Why would they rate the amp at 800w if you're saying that isn't correct? Thanks. Mike.


For sales dah! (land fills are loaded with blown or melted 811 tubes from AL811 series amps) Look at the AL80b, it is "rated" at 850 watts and has twice the dissipation of 4 ea 811's and twice that transformer mass. Which is a real 800 watt amp and which is greatly over rated? When AL811 amp was designed there was a surplus of tubes and they were cheap to replace.

When you look at a old SB 200 40 years old and still going, and some with original tubes, its two tubes were rated at 320 watts continuous dissipation and it was a good 600 watt amp. (4 ea 811's are only rated at 180 watts continuous) When you look at any amp you want it to have a safe continuous dissipation rating equal to 1/2 of rated output (more is better) This is why many like 8877 amps because with a rated 1500 watt dissipation as it loafs with approx 750 watts dissipation at 1500 watts out. Same with a pair of 3cx800 rated ate 1600 watts or a pair of 3-500z's rated at 1000 watts.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
WD8T
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Posts: 259




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« Reply #20 on: August 12, 2016, 10:15:51 AM »

Interesting. Thanks.

2) Would it matter which of the 4 tube slots I leave empty? Is there a certain order?

P.S. If I do the 572B, and I need a new plate choke for my current problem; I was thinking of getting a new parasitic. Would I get the 3 tube model like for the AL-811 instead of the 4 tube model for the AL-811H that I have?

I have an older 811H and replaced the 811's with three 572B's.  No mods were necessary and I believe you leave the socket closest to the fan empty.  Still runs the same as it did with the 811's and  I don't drive it to 800 watts.  I run it conservatively at 450-500w pep so those 572's will probably last my lifetime and beyond.
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W8JX
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Posts: 13268




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« Reply #21 on: August 12, 2016, 10:20:40 AM »

I don't drive it to 800 watts.  I run it conservatively at 450-500w pep so those 572's will probably last my lifetime and beyond.

You can safely run more power if you want. You will run out of power supply current before you hurt tubes.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
WY7CHY
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Posts: 933




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« Reply #22 on: August 12, 2016, 10:22:55 AM »

Thanks for all the feedback.

So, the first thing to do, is to find out what popped. Hopefully it's something simple like the plate choke. It could be a dual problem. A bad tube AND the plate choke. Either is ok with me. Just hoping it's not more into the tuned circuits, power supply, etc.

I guess I'll start looking at it tonight.

Thanks again for all the input. And for the future info of using 572b tubes. later..... Mike.......
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
WY7CHY
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Posts: 933




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« Reply #23 on: August 12, 2016, 10:26:14 AM »

I don't drive it to 800 watts.  I run it conservatively at 450-500w pep so those 572's will probably last my lifetime and beyond.

You can safely run more power if you want. You will run out of power supply current before you hurt tubes.

This brings up a question. If the ORIGINAL specs say that 65 watts input is about max for getting max out of the amp..........
And that you shouldn't put more than 80 watts input to the amp.............
Does that mean I could SAFELY run my transceiver barefoot at 100w; and when using the AL-811H (With 3 572b tubes), I could leave the output of my transceiver at 100 watts going into the amp.

Things that make you go hmmmmmmmmmm.

Thanks. Mike.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
Member

Posts: 13268




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« Reply #24 on: August 12, 2016, 10:38:25 AM »

I don't drive it to 800 watts.  I run it conservatively at 450-500w pep so those 572's will probably last my lifetime and beyond.

You can safely run more power if you want. You will run out of power supply current before you hurt tubes.

This brings up a question. If the ORIGINAL specs say that 65 watts input is about max for getting max out of the amp..........
And that you shouldn't put more than 80 watts input to the amp.............
Does that mean I could SAFELY run my transceiver barefoot at 100w; and when using the AL-811H (With 3 572b tubes), I could leave the output of my transceiver at 100 watts going into the amp.

Things that make you go hmmmmmmmmmm.

Thanks. Mike.


I never use rated drive level blindly. When I set drive level of a amp I watch input vs output power as I increase drive. When you reach a point where output power no longer increases at same rate as drive (ie loss of linearity) I stop increasing drive and reduce it slightly. This setting you give you best audio and best linearity of signal amplification regardless of actual power output. With AL811 amps this is usually between 40 and 50 watts. With my amp this happens around 900 to 1000 watts out with 55 watts drive. (BTW my old Dentron amp uses 4ea 572's and a bigger transformer with a higher voltage too)
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Ham since 1969....  Old School 20wpm REAL Extra Class..
WY7CHY
Member

Posts: 933




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« Reply #25 on: August 12, 2016, 10:46:09 AM »

Thanks. I tune the same way. Gradually increase input power until either: a) I don't get any more power out of the amp; or b) I get close to maxing grid or plate current. Then I back it off.

I guess what I was thinking is; if the 811a were spec'd in the manual of not exceeding 200ma grid and 750ma plate, (Something like that); I would think that the 572b could handle MORE; and as such; you could probably push more power into it.

From all the reading/research I've seen, no one sees an "Increase in Power" using the 572b vs the 811a (In the AL-811 series amps). So I would assume that it will tune about the same. Thanks. Mike.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
Member

Posts: 13268




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« Reply #26 on: August 12, 2016, 11:01:30 AM »

Thanks. I tune the same way. Gradually increase input power until either: a) I don't get any more power out of the amp; or b) I get close to maxing grid or plate current. Then I back it off.

You miss point here. It is not for maximum output power when setting drive. It is set at point where power out increases slower as drive in increased not at point where ther is no more increase if you want best audio and linearity.

I guess what I was thinking is; if the 811a were spec'd in the manual of not exceeding 200ma grid and 750ma plate, (Something like that); I would think that the 572b could handle MORE; and as such; you could probably push more power into it.

811'a are rated 175 ma max or 700 for 4 of them not 750. Also 700 does not mean it is fine because you can exceed rated dissipation at less than 700 ma unlike a amp using true high power tubes. Have to look at big picture


From all the reading/research I've seen, no one sees an "Increase in Power" using the 572b vs the 811a (In the AL-811 series amps). So I would assume that it will tune about the same. Thanks. Mike.

Yes it tunes same
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KF7CG
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Posts: 1212




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« Reply #27 on: August 12, 2016, 11:06:24 AM »

You all may be missing a point also. He should be checking the output too. Sometimes the plate meter switch goes flaky and you don't get a reading at all in one position or the other.

KF7CG
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W8JX
Member

Posts: 13268




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« Reply #28 on: August 12, 2016, 11:12:54 AM »

You all may be missing a point also. He should be checking the output too. Sometimes the plate meter switch goes flaky and you don't get a reading at all in one position or the other.

KF7CG

It read plate voltage and if no change when keyed choke is likely open.

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Ham since 1969....  Old School 20wpm REAL Extra Class..
KM1H
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Posts: 4722




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« Reply #29 on: August 12, 2016, 11:47:42 AM »

Amazing to note that all or most those questions are repetitive on here for years and with 300+ posts I would have thought an archive search would have been done first.
The AL-811 series of amps are about the most poorly designed and spec'd that Im aware of.
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