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Author Topic: Made the 10M Mod to Ameritron AL-811 / Very High SWR  (Read 15043 times)
KB1TJY
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Posts: 257




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« on: August 06, 2011, 10:54:18 AM »

Hope everyone is having a good weekend.

I made the 10M modification to the Ameritron AL-811 and as they mention could happen the SWR did blow through the roof.

The method they state to correct is as follows: "Input Circuit Tuning: If high SWR occurs at the input of the amplifier, adjust the tune-input circuit with a 01. inch hex TV Tuning Tool. Adjust the slug for low SWR when the amplifier is transmitting and tuned properly".

(1) I take it this .01 inch hex TV Tuning is just an ordinary hex of the appropriate size?

(2) With reference to the 'slug', I assume (since they do not state) that this 'slug' is located through the opening ("10M") on the rear of the Amp?

Any other advice greatly appreciated.

As always, many thanks.

73's,

Lyman
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K7KBN
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« Reply #1 on: August 06, 2011, 11:47:59 AM »

It has to be a NON-METALLIC hex tool.  Plastic.  If you use a regular metal Allen wrench it'll detune the input circuit and when you remove it you might be a lot further off than when you started.  You can find these tools on line at many of the usual places.

Yes, you will be adjusting the slug in the 10 meter input coil.  This also very likely affects the amplifier's  input on 12 meters as well.
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73
Pat K7KBN
CWO4 USNR Ret.
WB2WIK
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Posts: 20559




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« Reply #2 on: August 06, 2011, 01:17:26 PM »

I'm surprised it didn't match well, unless it was a used amp and somebody screwed around with it.

The Ameritron amps I've used (several) all came through with a good match on 10m right out of the carton.

Did you "tune up" the amp on 10m (not the input coil, but the plate tuning and loading)?  That effects input SWR.  If the amp isn't tuned up on 10m, its input SWR won't be very good, either.

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KB1TJY
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Posts: 257




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« Reply #3 on: August 06, 2011, 02:53:14 PM »

It has to be a NON-METALLIC hex tool.  Plastic.  If you use a regular metal Allen wrench it'll detune the input circuit and when you remove it you might be a lot further off than when you started.  You can find these tools on line at many of the usual places.

Yes, you will be adjusting the slug in the 10 meter input coil.  This also very likely affects the amplifier's  input on 12 meters as well.
Ah...the light came on. It's been so long since I've seen or used one (HS Electronics in fact) I'd forgotten about them being plastic and the need for being plastic. Thanks!
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KB1TJY
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Posts: 257




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« Reply #4 on: August 06, 2011, 02:58:09 PM »

I'm surprised it didn't match well, unless it was a used amp and somebody screwed around with it.

The Ameritron amps I've used (several) all came through with a good match on 10m right out of the carton.

Did you "tune up" the amp on 10m (not the input coil, but the plate tuning and loading)?  That effects input SWR.  If the amp isn't tuned up on 10m, its input SWR won't be very good, either.


This is a new Amp which I purchased a few months ago. As shipped from the factory 10M is disabled unless and until you make the the modification. As such you can't tune it until you make the modification....a Catch-22 if you will. Ameritron does provide for the event that SWR is high so it's not necessarily unexpected.

Unless you made the modification, how are you using 10M right out of the carton?

Thanks!

Lyman
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KE3WD
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« Reply #5 on: August 06, 2011, 03:32:19 PM »

Well, one would like to think that the manufacturer paid attention to adjusting the 10 meter input at calibration and testing time, but apparently either they do not, or somehow yours got by without it. 


73
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WB2WIK
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« Reply #6 on: August 06, 2011, 04:14:13 PM »


Quote
Unless you made the modification, how are you using 10M right out of the carton?

Thanks!

Lyman

I snip the wire when I first remove the cover to install the tubes, so it's "10m ready" as soon as I put the cover back on. 

Even if the input SWR appears high, you can still drive the amp and tune it up.  Output tuning does effect input tuning.

It's certainly possible that the factory simply forgot to tune the input for 10m, and maybe others have seen this, but I haven't.

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KD8GEH
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« Reply #7 on: August 09, 2011, 01:40:52 PM »

Sounds strange, something going on.

Have you checked the antenna direct from rig on 10 with the amp out of line? Are you using a tuner? Big enough to handle the power?

Make sure your jumpers are good and maybe make sure the correct wire is clipped again.

Mine was fine oput of the box as well.

73  De   Dave KD8GEH
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KB1TJY
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Posts: 257




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« Reply #8 on: August 09, 2011, 06:01:50 PM »

Sounds strange, something going on.

Have you checked the antenna direct from rig on 10 with the amp out of line? Are you using a tuner? Big enough to handle the power?

Make sure your jumpers are good and maybe make sure the correct wire is clipped again.

Mine was fine oput of the box as well.

73  De   Dave KD8GEH
Dave,

I've definitely clipped the correct wire but am wondering (being relatively new to Amps) if I am misunderstanding what is meant by "If high SWR occurs at the input of the amplifier".

I am going from an FT-2000 --> AMP --> Palstar AT2K --> Hustler 6BTV Vertical.

Any assistance greatly appreciated.

Thanks and 73's.

Lyman
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KA5N
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« Reply #9 on: August 09, 2011, 06:39:46 PM »

First you really need a dummy load.  Then connect the FT-2000 to the amp and the amp to the dummy load.  Amp switched to 10 meters, FT-2000 on 10 meters CW.  Feed power into the amp (start with 20 watts until you get things tuned ballparkwise) and tune the amp for maximum output.  You will need a power meter between the amp and the dummy load.  You could use the Palstar if it has a bypass setting.  Only key the rig and amp when you are making measurements or tuning.  Don't tune for extended periods. Once tuned, the input SWR should be indicated on the FT-2000 (I am not familar with that rig but surely it has an SWR meter built-in).  If the SWR is less than 2:1 you should be close to OK.  Increase drive power to about 50 watts and check amp tuning.  Check input SWR.
You should have already done the same procedure on the other bands.
If all has gone well the SWR should be OK  (less than 1.5: 1)  if swr is higher then using a correct tuning tool adjust the 10 meter slug until you get a suitable reading.  Then
stop.
If you try to tune things without using a dummy load they don't usually go right.
And with  a transceiver, amplifier, tuner, and antenna all connected you basicly  don't
know what is going on.
Good Luck   Allen
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KB1TJY
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Posts: 257




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« Reply #10 on: August 09, 2011, 06:56:51 PM »

First you really need a dummy load.  Then connect the FT-2000 to the amp and the amp to the dummy load.  Amp switched to 10 meters, FT-2000 on 10 meters CW.  Feed power into the amp (start with 20 watts until you get things tuned ballparkwise) and tune the amp for maximum output.  You will need a power meter between the amp and the dummy load.  You could use the Palstar if it has a bypass setting.  Only key the rig and amp when you are making measurements or tuning.  Don't tune for extended periods. Once tuned, the input SWR should be indicated on the FT-2000 (I am not familar with that rig but surely it has an SWR meter built-in).  If the SWR is less than 2:1 you should be close to OK.  Increase drive power to about 50 watts and check amp tuning.  Check input SWR.
You should have already done the same procedure on the other bands.
If all has gone well the SWR should be OK  (less than 1.5: 1)  if swr is higher then using a correct tuning tool adjust the 10 meter slug until you get a suitable reading.  Then
stop.
If you try to tune things without using a dummy load they don't usually go right.
And with  a transceiver, amplifier, tuner, and antenna all connected you basicly  don't
know what is going on.
Good Luck   Allen
I had a Dummy Load (was married to her for 20 years) but got rid of that one. Actually it was the other way around but whatever!  Grin I did acquire another dummy load, forgot to mention that in my last post. I will try what you suggest and post the results here. The Palstar AT2K does in fact have a Bypass to which the Dummy Load is connected.

Thanks,

Lyan
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WB2WIK
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« Reply #11 on: August 09, 2011, 07:03:03 PM »

I'd always make sure to use the dummy load when first tuning "anything."

GG amps input tuning changes with termination.

Again, "anything's possible," and maybe Ameritron doesn't tune the 10m slug at the factory (I have no clue) but the Ameritron amps I've used, and I've owned a few and still own one, came through "out of the box" tuned up just fine on 10m.
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W8JI
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« Reply #12 on: August 10, 2011, 07:55:49 AM »

I would check all of my cables first BEFORE doing any golden screwdriver work. Nearly 100% of the time ten meter SWY will be very low, because it is a normal part of testing.

Nearly all of the time (but not 100%) any SWR problems turn out to be:

1.) A bad jumper cable

2.) Operator error, like leaving the radio's tuner on when using the amp or having something with an impedance bump in line.

73 Tom



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KD8GEH
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Posts: 464




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« Reply #13 on: August 10, 2011, 12:23:38 PM »

I agree with Tom.

If you dont have a dummy load, start with the rig (no autotune), then tuner and antenna. See what the swr is straight thru the tuner.

I'll bet you have a bad jumper or something like that.

Dave
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KB1TJY
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Posts: 257




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« Reply #14 on: August 11, 2011, 10:08:23 AM »

I agree with Tom.

If you dont have a dummy load, start with the rig (no autotune), then tuner and antenna. See what the swr is straight thru the tuner.

I'll bet you have a bad jumper or something like that.

Dave
Thanks Dave. I spoke with Ameritron T/S and they're of the opinion that 10M wasn't calibrated prior to shipment. So I'm waiting for the proper hex tool to arrive within the next few days. The input SWR is 4.0 at the radio...high.

Appreciate the input, many thanks!

73's,

Lyman
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