K4 to la1k interface cable

Making a K4 to la1k interface cable is not hard if you know the basics.  It is just connecting the right wires to the right places and there only 6 of them for this set up. The first step is to get the parts you will need for this little project.

To go from the amplifier you will need DB9 female connector with cable using the Yaesu jack on the rear of the LA1K.

K4 to la1k interface cableK4 to la1k interface cable



The  K4 uses a DB15/DE15 male connector. I use the breadboard type with screw terminals, this removes the soldering and is easier to make changes. The image above shows the 4 pack of DB15 connectors which gave me two males and two females. I like having parts on hand when I need them.

Make sure you order a long enough cable. Both the K4 and LA1K are also compatible with Kenwood’s interface connections but a male DB9 with wire would be needed for those connections. I believe there are only 3 wire connection with the Kenwood set up.

LA1K pin outK4 Pin out

You will need to pull these two wiring diagrams from the manuals of the K4 and LA1K. They will show the wire connections of the radio and amp.

Interface Cable Pin Out

K4 to la1k interface cable

On the diagram above is all the information needed to make the cable. The upper left shows the wire connection. The writing in red shows the data from the two manuals. These codes are used in band data interface cables.

The DB9 connector with cable I ordered did not have the wire ends marked so I had to trace them with a multi meter. If you purchase the same cable here, the wire colors and above chart will work without having to trace them.

The Band

  • Pin 13 goes to Pin 2
  • Pin 3 goes to Pin 1
  • Pin 9 goes to Pin 9
  • Pin 14 goes to Pin 8

The keying circuit needs ground wire to work. The DB15 has two of them on Pin 5 and Pin 12 while the DB9 has one on pin 6. I used pin 12 because of tis location in the connector.

  • Pin 12 goes to Pin 6

Keying the amplifier can be done two ways, It can be keyed through the interface cab le or by using the RCA phone jacks. If you use an automatic antenna tuner you will want to use the RCA phono jacks. The tuner will delay the amplifier from keying until the tuner finishes.

If you use a manual antenna tuner like I do, you can have the interface cable handle the keying. Make the connection below:

  • Pin 10 goes to Pin 7

K4 to LA1K Interface Cable

This will finish the cable connections, so you can close up the DB15 connector and give it a try. Once the cable is together, connect the DB 15 to the Elecraft K4 using acc. jack. The DB 9 will connect to the Palstar LA1K with the Yaesu jack. If you used the RCA phono jacks for keying you will want to connect them now.

When first testing the cable, keep the amplifier in stand by mode and try all the bands to ensure they change properly. Then put the amplifier in operate mode, and see if it keys the amp correctly. Try this on low power to ensure it keys correctly.

ALC Connections

If you use the ALC to keep the amp from over driving by accident, you can follow the instruction from Palstar. I know there are specific instructions on making this work.

Get on the air and make some contacts.

By Vince

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