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Author Topic: Ameritron AL-80a to Icom IC-756ProII  (Read 4764 times)
AE6RF
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« on: August 18, 2007, 04:22:03 PM »

Greetings,

The Ameritron AL-80A has a negative 0 to 20 V ALC.
The Icom IC-756ProII has a negative 0 to 4 V ALC.

May I please have a clue as to how to interface them?

The assumption is that as the Ameritron gets overdriven it will decrease the ALC voltage starting at 0 and moving negative until it is happy again.

If the assumption is correct, the Icom will be "as low as it can go" by the time it hits -4 V, so it *should* never see -20V.

Clue please?

Thanks es 73 de Donald
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W5RKL
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« Reply #1 on: August 18, 2007, 05:37:44 PM »


I think you may be reading too much into the -4 and -20 transceiver and linear amplifier's ALC voltage.

Simply connect your transceiver to the AL-80A as shown in the manual on page 2 and adjust the AL-80A's ALC adjustment as outlined on page 1 and you will be fine.

You can use cheap stereo interconnect cables to connect the ALC and RELAY connections between the amplifier and the transciever since both voltages are DC not RF.

73's
Mike W5RKL

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K6AER
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« Reply #2 on: August 18, 2007, 09:09:49 PM »

If you connect the -12 VDC ALC to the Pro II ALC input you will shut off the IC756 Pro II transmitter on voice peaks. The R/C constant in the Pro III will take about 3 seconds to recover. You can place some series resistance to cut down the voltage output to -4 VDC maximum but there is an easier way.

The Pro II has an excellent power setting capability. Just set the power output to a level so as not to overdrive the AL80B (about 55 watts) and leave the ALC disconnected. ALC is a throw back to the older tube type radios form 20 years ago when they had poor power control. In today’s modern transceiver ALC is not needed.
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W5RKL
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« Reply #3 on: August 18, 2007, 11:27:41 PM »

I'm sorry K6AER, but the statements you provided about ALC are simply not true.

The 756ProII manual, page 18, clearly shows how to connect a non-Icom linear amplifier such as the Ameritron AL-80A to the 756ProII. In addition it states to consult amplifiers manual for proper ALC voltage level, 0 to 4 VDC negative.

The AL-80A manual, page one, gives clear procedures for adjusting the amplifiers ALC. Also, on Page 2 of the manual, connection procedures and pictorials are provided to connect the amplifier to a transceiver.

The AL-80A amplifiers ALC pot, located on the rear panel, controls the amplifiers ALC negative voltage output level between 0 and 20VDC.

As long as the procedures outlined in both manuals are followed, the 756ProII and the AL-80A should be quite happy together.

Donald, if you are still confused, do not understand what I have said in both of my posts, simply pick up the phone and call Ameritron and/or Icom and discuss it with them. They have 800 numbers and will only cost you your time.

73's
Mike W5RKL
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KE3WD
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« Reply #4 on: August 19, 2007, 09:19:03 AM »

ALC Adjust to match rig is indeed a trimpot on the back of the AL-80A, located just below the ALC out jack.  



!

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N3JBH
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« Reply #5 on: August 19, 2007, 12:08:54 PM »

Pick a band example 40 meters and tune the amp for maximum output while staying in the parameters of the amplifiers recommendations. Now adjust the ALC pot in the back till the radio just starts to reduce power. Once you find that spot bump the ALC pot back up ever so slightly.  At this point you will have adjusted the ALC properly. It is the easiest way I know how to explain it.

As far as saying it shuts off you radio if you go past the peak. That is not true. It simply reduces your drive to the point your amp is staying in its settings. And saying it was a throw back to the old days of tube transmitters may be true. But I like to think of the ALC circuit as a governor. Away to be sure you don’t over drive anything.  Just seems to me to be free insurance item the manufactures gave you to help save the amp. And hopefully to keep you from over driving and causing splattering etc every where.

So plug in the ALC and use it.
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K8AC
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« Reply #6 on: August 19, 2007, 07:22:38 PM »

The Icoms have used the same ALC voltage scheme for as long as I can remember.  I've used the AL-80B with an IC-765 and an IC-781, which will both cut off near the -4VDC level.  I don't know if the ALC implementation the AL-80A is the same as on the AL-80B, but if it is, just follow the adjustment procedure in the amplifier manual and it will work perfectly.  
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KE3WD
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« Reply #7 on: August 19, 2007, 08:40:19 PM »

That trimpot on the back is wired as a voltage divider!  

Follow the directions on adjustment and it will end up dividing 20V by 5.  


!
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K6AER
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« Reply #8 on: August 20, 2007, 11:50:19 AM »

I stand by my statement. If you place -12 volts on the ALC input to the Pro II it wil shut of the transmitter for about 3 seconds.

Second statement is true also, You don't need the ALC conneccted to the Pro II or III. Just limit your power to the amplifier by setting your Pro power control to maximum power for linear operation on the AL-80 or any amplifier.
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KE3WD
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« Reply #9 on: August 20, 2007, 07:45:23 PM »

Sigh.  

If the voltage divider pot at the back of the amp is set properly, no more than 4 VDC will ever be seen by the rig's ALC input!  


By design.



!
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