Heathkit Keyer on the Air

Thursday, I took the Heathkit keyer apart, spread out the schematic and began poking around. It looked to me like everything was working the way it should, so I buttoned it all back up, built a cable to connect it to my IC-735, and voila it keyed the rig perfectly.

My only guess as to why it didn’t work right before is that I had the positive and negative contacts swapped. If you’re keying the transmitter with a straight key, swapping them doesn’t matter–the key is only a mechanical switch after all, and the current doesn’t care which way it flows through a switch. But the output of the keyer is a transistor, and current flows only one way through a transistor, so you have to connect it properly.

Instead of using the capacitive paddles built into the keyer, I’ve opted to use the Bencher paddle. I played around with the sensitivity adjustment for the capacitive paddles, but I just couldn’t find a setting that wasn’t too sensitive. As a result, I was getting a lot of phantom dits.

The problem with using the mechanical paddles is that instead of using a stereo phone plug, Heathkit decided to use a small header. This is, of course, a lot less standard than a phone plug, and the local Radio Shack did not have the proper connector. To use the keyer today, I had to use some clip leads and Mickey Mouse it. I hope that Purchase Radio will have what I need, but if not I may have to modify the keyer to accept a phone plug.

The good news is that I made eight contacts today using the paddle/keyer combo. I asked the operators on the other end to be a little patient, and fortunately for me, they were, for the most part. I think I got better along the way, although during the last contact, I got tired and began to lose concentration and started making a lot of mistakes. All in all, though, I think I’ll like using the keyer once I get proficient with it.


  1. I picked up a Heathkit HD410. It didn’t come with cables. I also picked up an ICOM 745.
    Saw your note above and thought you could help me out with the connection.
    What exactly did you use to connect it?
    Would appreaciate any help…..I’ve been too lazy to look into it yet, as I’m still practicing the learning on CW.
    Thanks / 73 / VE3EEZ

  2. Dan KB6NU says:

    The model number for my Heathkit keyer is SA-5010, so I’m not exactly sure what to tell you.

    One thing I can say, though, is that you probably want to use the output that is switched to ground when keying. To figure out which output this is, connect a 12V source to the outputs through a 10k resistor and measure the voltage. The proper output will measure +12V when not keying and close to 0V when keying.

  3. Charles Lear says:

    Hi I am looking for the number of the heath kit transmitter that worked with the ssb 303 reciever
    when connected together with their cable. I have the 303 and am hunting for the transmitter. I am building the linear from the 14 edition of the handbook which has a pair of 811s in push pull and want to make the transciever by finding the companion to the 303. I hope you have the answer.
    Thanks for any help you can give me.
    K3IKJ Bud
    Charles F. Lear Jr.
    280 Penna. Ave.
    Catasauqua,Pa. 18032

  4. Dan KB6NU says:

    Hi, Bud–

    It looks like the transmitter you’re looking for is the SB-401. See http://www.rsbac.com/sb303.html.

    73! Dan KB6NU

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