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Author Topic: Low power on some bands AL 811  (Read 1391 times)
K6MWL
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Posts: 2




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« on: April 04, 2014, 12:28:47 PM »

I have an AL 811 that works great on 75/80, 40, and 20. Radio and amp tuned up properly, I get lower power on 15, 18, and 10. Maybe 200-300 watts, with 65 drive. My station is 2nd floor, and not grounded. Any ideas. It works killer on 75/80, 40, and 20. Thank you. Mike K6MWL
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NO2A
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Posts: 800




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« Reply #1 on: April 04, 2014, 02:37:08 PM »

First I`d try the amp into a dummy load. If it puts out normal power with the dummy load that rules out the amp. Make sure your rig is delivering full drive on those bands.
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WX7G
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« Reply #2 on: April 04, 2014, 03:23:05 PM »

If you don't have a dummy load the antenna will work as a test load as long as the VSWR is 2:1 or less. 
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KF7VXA
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« Reply #3 on: April 04, 2014, 06:20:52 PM »

On mine, 10 & 12 meters has a little less power than the others but I think that has more to do with the electronics on those bands as well as tuning the coil for one band or the other.
I'd bet you may have high SWR on the lower bands and your driver is folding back power. The dummy load is going to be your best friend for seeing exactly what is going on.

73's John
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WB2EOD
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« Reply #4 on: April 04, 2014, 08:46:40 PM »

Lower output on ten meters is more or less normal.  I run the 811H and  on ten meters the the output is around 20% lower than on twenty meters (with comparable drive).
Try this:
While running the amplifier into a suitable dummy load, check the SWR between the radio and the amplifier.  If the 811's input circuit is not properly tuned, the amplifier will present a high SWR to the radio.  As the SWR approaches around 2:1 the radio will probably start to fold back the power reducing the drive to the amplifier
The input tuned circuit is adjustable but I have not found it necessary to touch it 
In the 15/17 and the 10/12 position, the input tuning is something of a compromise between the 2 bands.
Whatever you do, don't increase drive beyond the point where there is no additional output.

Hope this helps
73
WB2EOD
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K4RVN
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« Reply #5 on: April 04, 2014, 09:45:54 PM »

Having owned a three tube AL 811 for 3 years I can agree with John. Connect it to a dummy load and see if it will load 500 watts at 65 amps drive. If not then you will know that it is your amp.
I don't suspect the tuned input on 15 and 18  since both have low outputs on the same bandswitch position. If it loads normal on 12 and not on 10 it could be your tuned input is set to favor 12. I would not bother it at all until I used a dummy load to check it out. Good luck and letus know what you find out.My 811 would load my hex beam almost full power on 12 and 10 meters so a couple hundred watts less between bands is not a normal situation.

Frank
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K6MWL
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« Reply #6 on: April 05, 2014, 07:59:11 AM »

Thank you all for taking the time to help. Ive heard things about not being grounded. I need to get a dummy load, Thanks again all! Mike K6MWL
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KF7VXA
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« Reply #7 on: April 06, 2014, 07:52:58 PM »

One other thing I've noticed. I usually use a Gap Challenger vertical. I love the antenna and have made contacts all over the world with it. That said, it seems that my wire horizontal dipole will load about 50 watts more than the vertical, so it may have to do with the antenna also. It is most likely SWR related as the Gap is a little different than most other antennas. 50 watts really makes zero difference on the other end anyway. I need to get a better meter anyway, I know what I have now reads on the low side.

As long as your amp is working correctly, a difference of 100 watts won't really be noticed anyway and with the way most meters are today, you may be putting out more power than you think you are anyway. I have a LDG 600 watt tuner and it shows 600 watts on  15, 20 and 40 when I carefully load the amp, it does not like to load 10 and 12 with the vertical, but will load 10 on the horizontal dipole. I prefer it to stay at about 500 watts, so I'll lower the transceiver power when I see the LDG showing that much power.
I don't have a 17 meter antenna yet, but will be buying a 17 meter mono band Gap as I want a compact antenna, not having to string another horizontal dipole and I know the Gap 17 will work very well and very much want to work 17 meters; it's a great band.
73's John KF7VXA
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