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Author Topic: ICOM 756 Pro 2 with Ameritron ALS-600  (Read 3161 times)

Posts: 165

« on: October 09, 2007, 04:48:49 PM »

I recently purchased a used ALS-600 amplifier and attempted to interface to my ICOM rig. It should be easy as the Ameritron has a modest 100 ma. at 12 vdc for keying and the ICOM relay is supposed to be able to handle 500 ma at 16 vdc.

Both rig and amp use standard phono plug cables for ALC and relay keying, but I could not get the amplifier to key up. The small relay in the ICOM 756 Pro 2 does not engage the armature when the rig is keyed. I pulled the bottom cover and noticed one of the multipin connectors seemed loose and plugged in in better but no change. I have not checked to see if there is a control voltage present to the relay from the relay driver circuit.

Note: After I bought the 756 Pro 2, it malfunctioned and would not turn on and was repaired under warranty for a defective wiring harness. Since being repaired it has worked well for the past couple of years but I have never used an amplifier, in fact, this is my first amplifier.

As far as I can tell, there is no software or hardware switch that needs to be engaged.

The rig itself keys fine from software control through the CI-V for digital modes.

Two questions:

1) Has anyone heard of this problem with this particular rig or know of any fix?

2) Rather than repair it, what do you think about using the PTT line available on one of the DIN plugs on the back and using either some kind of purchased interface or make a basic interface to a small relay to switch the amplifier on when the PTT is engaged?

Thanks for any help you can give.

Rick, KV9U


Posts: 5743

« Reply #1 on: October 09, 2007, 05:10:30 PM »


The keying relay in the 756 Pro series is more then capable of keying the ALS-600 amplifier. You should fine out why the relay is not keying. Some things to look for:

Is the keying relay transistor being biased on when PTT is activated?
Is the relay being keyed?
Are the relay contact making contact?
Is the wiring good between the Key Out jack (RCA) and the relay?

I would fix the radio first for it affects the resale value.

Also short the cable to the ALS-600 key line and make sure the amplifier is keying.


Set the radio output for maximum drive to the amplifier (50-60 watts) and leave it there. The ALC on the 756 Pro series is very good.

Posts: 817

« Reply #2 on: October 09, 2007, 05:11:00 PM »

I would check to see if it is the radio that is not keying, the amp is not being keyed or the cable is not passing the keying control. Two checks will tell. First plug your RCA to RCA cable into the keying jack on the amp and short the free end. The amp should go "Chunk" (or at least that what my amp does) indicating the relay has energized. Next take the same cable (after disconnecting it from the amp) and plug it into the rigs keying jack. Put a ohm meter set to a fairly high resistance range to limit the current on the free end and key the rig. The meter should show the relay closing giving you a short at the end of the cable. If the first test works, the rig is at fault. If the second test works, the amp is at fault. If neither happens the cable is bad.

I built a keying interface for my IC-756 and SB-200. It has a spiffy little LED it indicate when the rig has keyed the opto-isolator so I can tell where my keying signal goes away (like when I move the roll around stand the amp is on and pull the RCA plug out of the back of the amp). I also put a bypass function in my interface so I can have the amp idling and flip the switch to engage the amp without having to let it warm up.

Hope that helps. Let us know what you find out.

Clint - W5CPT
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