Automatic Keyer for CW Using Relays

 

           

                

                            

                                     CLICK to enlarge

       In the days before Single Side Band AM (single side band is AM) hams keyed transmitters by hand using Morse code which consisted of dots and dashes. Several atomic keyer circuits were published in CQ and QST to assist this endeavor. The circuit above which generates automatic dots and dashes was designed by W3FQB and it was unique as it utilized selenium rectifiers to isolate the dot and dash circuits thus eliminating a relay. Some of the earlier circuits used 3 relays.

 
                          

         Selenium rectifiers were a big deal in the 1950's. Replaced later by smaller diodes.
 
                           

               Theory of operation taken from the original article. 
 
                  

           The pots R4 and R5 control dot and dash length. R1 controls the speed. Use 9 volt batteries in series for power. The two diodes (SR 2 and SR1) replaced the selenium rectifiers and are mounted in the center. I used 22uF capicator for C1 and C3 and then 22uF and 10uF in parallel for C2 this gave me a nice mid range speed of around 8 WPM.
 

             
      I used several different types of relays - - - the relay at the upper right RY1 must have a set of normally closed contacts which open when voltage is applied. The keyer "paddle" provides a plus voltage into the two clips at the top to provide voltage for dots and dashes.
         The keying relay at the bottom left only needs one set of contacts that close when voltage is applied to the coil. The other relay at the bottom right is an emergency spare.

 

                         Note the use of PC board squares for soldering components. A modern bread board.

 
                 

        The 255A "polar relay which has two coils and can be found in junk boxes at ham fests. The polar relay can be used even though it is not 5000 ohms but it is very sensitive. There is enough "mechanical" bias which will allow it to be used as a keying relay. If the lack of bias bothers you and keeps you awake at night then bias the other winding with a 9 volt battery and a 100K pot. BTW the 255A relay is an excellent source of parts for home made CW keys. Thousands and thousands of the 255A relays were made by different manufacturers for teletype operations and today they are usually thrown in the trash barrel at hamfests. I always look through the trash barrels before leaving a hamfest - - - my shop is beginning to look like a hamfest.
 
                       
 
        Half the fun is going through your box of relays.
 
                       

               Several reed relays were tested. This one measured at 5000 ohms. Perfect. The only catch is there is only one set of contacts which are normally open so this particular relay can only be used for the final keying relay RY2. RY1as RY1 needs a set of contacts that are normally closed. There were reed relays made with double throw contacts so look for them.
 

                 

        Most of the early electronic keyer "Paddle Keys " were made from back to back surplus military keys. The clear plastic paddles replaced the knobs and were made from Plexiglas found in a trash barrel at a USAF scheduling office in 1963. The military throws away a lot of stuff. Plexiglass was a big deal then. J-38's were often used for keyers and were a buck a piece down on Market Street in San Francisco. A sardine can was used as a mold for the lead base but remove the sardines first. Later my lead key bases were painted black to prevent lead ingestion and to provide stealth.
                   Improvise - Adapt- Overcome

       

 

                          
                                          Photo by N9SE

               Here is a simple key using a hacksaw blade as a base. Also known as a Cootie" key. This one made by N9SE. Note the blade "throw" adjustment made by using the placement of the nails.

 
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