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Author Topic: Ameritron AL 811. Gird Current  (Read 12852 times)
W8JX
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« Reply #30 on: March 07, 2012, 01:42:15 PM »


                                                WX7G
                                               calculated
Pout    Plate I     Power DC    Power dissipated     Efficiency         W8JI measured Power Dissipated (see REFERENCE below)
100W     0.41X       377W         277W                 37%                300W
200W     0.58X       534W         334W                  37%                330W
300W     0.71X       653W         353W                  46%                340W
400W     0.82X       751W         351W                  53%                350W
500W     0.91X       837W         337W                  60%                250W
600W     1.00X       920W         320W                  65%                270W

Actual measurements of an AL-811H have been performed by W8JI. Refer to Figure 5.

I seriously question the accuracy of this data. Something as simple as improper loading to adjust output can skew data greatly to the needs of a claim. I know first hand that when I reduce drive and properly tune amp that plate current is much lower and amp runs even cooler.

I used to have a lot of respect for Tom's data but after his story about a doctor supposedly dropping and loosing a lens implant in his eye several month ago I realize he is a story teller too. This data has little meaning without complete test procedures too to be able to dupplicate. Furthermore if we would to really believe these claims about 811 tubes and amps then Alpha and QRO and Commander that built amps with twin 3cx800's or twin 3-500z's or a 8877 wasted time and money as they could have used far less tube  and amp and "safely" had legal limit output. Why bother with 1000 watts, 1500 watts or 1600 watts rated continuous dissipation for 1.5kw out when you can supposedly "reliably" get 800 watts out of 4 tubes with only a combine continuous dissipation rating of 180 watts.
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WX7G
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Posts: 6055




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« Reply #31 on: March 07, 2012, 02:48:12 PM »

W8JX,
the AL-811 can run 600 watts SSB while operating the tubes within their plate ICAS plate dissipation ratings. This amp will not reliably run RTTY by tuning for maximum power and then backing off the drive. It will run RTTY by tuning for maximum power at reduced drive. The AL-811 manual mentions this and states that this cannot be done for SSB because the IMD increases at light plate loading.

This amp is admittedly limited, however the best way to minimize plate dissipation in SSB or CW mode is to operate at the full 600 watts.

To run continuous key down or RTTY at 1500 watts RF output, at an efficiency of 65%, the plate dissipation is 800 watts. Hence the need for two 3-500Z tubes, two 3CX800 tubes, or an 8877 tube. Amps using these tubes aim for the brick-on-the-key market or the RTTY contester.

Can you take this data for your tube amp and post it here? I no longer have a tube amp and must rely on you to take and present this data.

To match my calculated method and the measurement method apply drive and tune for maximum power. Do this so maximum power is equal to the full rated power of the amp. Next, without touching the loading or tuning controls, decrease drive to obtain 100 watts, 200 watts, and so on. Record the DC power input and the RF output power. Post this along with the plate dissipation (DC input - RF output).


« Last Edit: March 09, 2012, 08:00:18 PM by WX7G » Logged
AD6KA
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Posts: 2237




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« Reply #32 on: March 08, 2012, 01:08:09 PM »


I used to have a lot of respect for Tom's data but after his story about a doctor supposedly dropping and loosing (sic) a lens implant in his eye several month ago I realize
he is a story teller too.

Cheap shot, OM, cheap shot.
Ken, AD6KA
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W1QJ
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Posts: 1446




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« Reply #33 on: March 08, 2012, 06:12:49 PM »


I used to have a lot of respect for Tom's data but after his story about a doctor supposedly dropping and loosing (sic) a lens implant in his eye several month ago I realize
he is a story teller too.

Cheap shot, OM, cheap shot.
Ken, AD6KA

PLEASE. tell me where I can read this.  I must have missed this one.  I have heard where doctors have amputated the wrong limb so this may not be hard to digest after all. Thanks
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W8JX
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Posts: 5793




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« Reply #34 on: March 08, 2012, 07:07:17 PM »


I used to have a lot of respect for Tom's data but after his story about a doctor supposedly dropping and loosing (sic) a lens implant in his eye several month ago I realize
he is a story teller too.

Cheap shot, OM, cheap shot.
Ken, AD6KA

PLEASE. tell me where I can read this.  I must have missed this one.  I have heard where doctors have amputated the wrong limb so this may not be hard to digest after all. Thanks

It is medically impossible for two reasons. One there is a membrane between the inner eye and the "sac" that contains your lens that is not breached during surgery. Second, the fluid in the eye it not really a fluid but more of a thick jelly and even if this membrane was breached it would take force and effort to push something into inner eye and it would easy to find because it would be where you left it.

BTW it was not a cheap shot at all because I am not the one that made up the story about a lens being dropped in eye and lost for a few weeks and sold it as truth. I only called them out on its very obvious fabrication.
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WX7G
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Posts: 6055




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« Reply #35 on: March 09, 2012, 08:41:54 AM »

The "reduce TX power to reduce the temperature of the amplifier devices" is a powerful myth. It does seem intuitive but it is not only wrong but can increase the temperature of the amplifier devices.

I'll write an eHam article on this subject.

Let's take the case of a Class-B amplifier. The maximum efficiency possible is Pi/4 = 78.5%. This is found by the formula

efficiency = (Pi X Vout)/4V, where Vout is the load voltage as seen at the device (plate for a tube amp), and V is the B+ voltage. Here are the numbers for an ideal 600 watt Class-B amplifier:

RF output        DC input      Plate dissipation
100                   312             212
200                   441             221
300                   540             240
400                   624             224
500                  697             197
600                  769             164

« Last Edit: March 09, 2012, 01:09:27 PM by WX7G » Logged
W8JX
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Posts: 5793




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« Reply #36 on: March 09, 2012, 08:54:14 AM »

The "reduce TX power to reduce the temperature of the amplifier transistors" is a powerful myth. It does seem intuitive but it is not only wrong but can increase the temperature of the amplifier transistors.

If this was set in stone then your 100 watt rig would run nearly as hot at 20 watts out as 100 but such is not the case. SS devices are without question generally not as efficient as tubes in amps but circuit design and biasing also plays a roll here in efficiency at lower drive levels. Also I would not use Ameritron as the gold standard for proper SS amp design either.
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WX7G
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Posts: 6055




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« Reply #37 on: March 09, 2012, 12:10:45 PM »

W8JX, on March 05 you advocated running the AL-811 amp at 75% of full power so as to increase tube life (implied to reduce plate dissipation). This will actually increase plate dissipation. This is an example of the myth.

You don't care to accept my calculations for a class-B amp or actual measurements on the AL-811.

Will you measure the DC input and RF output of your tube amp and post the results here?

So that we are comparing apples to apples the procedure is to adjust the RF drive so that the amp makes rated power when tuned for maximum output. The RF drive is then reduced and measurements of DC input power and RF output power are performed without altering the tune and load controls.
« Last Edit: March 09, 2012, 08:01:29 PM by WX7G » Logged
W8JX
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Posts: 5793




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« Reply #38 on: March 11, 2012, 10:06:01 AM »

W8JX, on March 05 you advocated running the AL-811 amp at 75% of full power so as to increase tube life (implied to reduce plate dissipation). This will actually increase plate dissipation. This is an example of the myth.

You don't care to accept my calculations for a class-B amp or actual measurements on the AL-811.

Quite honestly I do not believe your observations because I know how my amp acts at lower power and drive levels. By simply not loading amp properly are reduced levels you can reduce efficiency. In next week or two when I get some time I will chart results I get here and will record drive level, plate current, power out and efficiency and various power levels.
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WX7G
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« Reply #39 on: March 11, 2012, 10:12:10 AM »

Sounds good. Please tune as noted; that is adjust drive with tune and plate controls adjusted for maximum RF output power such that that the rated maximum RF power is achieved. Then adjust only the drive power to achieve lower RF output power.

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KA2UUP
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Posts: 388




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« Reply #40 on: March 12, 2012, 12:42:56 PM »

Klas,

I had the same problem with an AL-811H some years ago.  After a lot of problems with runaway gris current, I sent the amp to Ameritron.  They found out that the resistor in the meter was intermittent.  This might be the problem.

73 DE Bert @ KA2UUP
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