Thursday, July 12, 2012

SS-64 Encoder installation into Kenwood TR-9000

Recently I had the opportunity to purchase a pristine Kenwood TR-9000 radio.  It was manufactured in the 1980s, but looks like it just came off the showroom floor.  I love these older Kenwood radios!  So far I have a:
  • TS-440S/AT for working HF
  • TR-7730 that I use for VHF packet and APRS
  • TR-9000 all mode 2m radio that I use for weak-signal work and now local ragchews
The only drawback to the older VHF radios is a lack of ability to encode CTCSS (PL) tones.  For APRS or packet use, this isn't an issue, so my 7730 is great at what it does.  However, I really want to use my new TR-9000 to participate in local nets, in addition to (trying) to work SSB.  Since this radio doesn't have a tone encoder, I have been unable to use it on local repeaters that require a subaudible PL tones to key up.  Enter the Com-Spec SS-64 encoder board.  For a whopping $30 I was able to purchase one of these babies to add this functionality to my Kenwood!

The installation process was much simpler that I had anticipated. All that was involved was taking the case off of the radio, removing one of the sub boards, and soldering three wires.  Boom, done!  To aid anyone that may be trying to do that, I have taken some pictures of what you need to look for.

There are three leads that are of primary concern with this board, red and black for power and ground, respectively,  and yellow for modulation.  The red and black are easy enough to figure out.  I connected them to the incoming 12V lead on the back of the radio, and to the chassis ground lead in the same location.

The yellow wire is a little more complicated.  It needs to be connected at the junction of the VR-2 variable resistor, and the C-16 capacitor.  Finding these required digging through the schematics and snooping around the boards themselves.  Here is a picture of the board that you will find them on:

This board is located in the back of the radio, under the top cover.  The specific two components that you are looking for are located in the bottom left of this picture.  Here is a close up (hint: look at the brown round thing standing up, and the green thing that looks like a tic-tac right next to it):

The tricky part is that you cannot solder to this side of the board, you will need to flip it over, then locate the proper pins to connect to.  Here is a picture to help you identify the proper pins:

I forgot to take any pictures of after I had solder the connections, I was too eager to talk on my local 147.120MHz repeater!  

I routed the rest of the cables from the under side of the radio since there is more room to install the encoder board there.  I used the double sticky tape enclosed with the board to mount it next to the speaker.  According to the instructions, you may need to make some fine-tuning adjustments to the frequency by adjusting a pot on the encoder board itself, but I did not find this to be necessary.

I hope that this has helped anyone that is trying to do this installation to this radio.  It may seem complicated, but it is fairly straight-forward if you approach it methodically.  Take plenty of pictures to remind yourself what cables went where, or take good notes.  But that holds true for any project.

My Parts List:
  • 1 x Com-Spec SS-64 encoder
  • 1 x Kenwood TR-9000 2m radio

Time to Completion:
  • Approximately one hour

This was a fun little project that added a tremendous amount of functionality to my radio!  There are several more mods in this radio's future.  An extremely knowledgeable ham that I talked to on the repeater (N4LGH) has mentioned a few, and I've been reading about a few, so stay tuned!


Richard, KK4JDO


  1. I recently picked up a tr-9000 and thought it would be fun to add the encoder. I read your post and the motivated me a little so I took of the top cover and guess what I found? I ss-64 encoder is already installed. I adjusted the dip switches to 162.2 and dialed in my local repeater. It works. I guess I don't get to do the project after all!