Henry (KA3MUF) -
Although Kenwood no longer makes the TU-79 CTCSS board (discontinued) - you have good luck!
PIEXX makes 13 different plug-in replacement CTCSS boards for Kenwood, Yaesu, and Icom radios.http://www.piexx.com/index.php?main_page=index&cPath=6
The "drop-in" replacement for your Kenwood is the TU-79px for $59.00http://www.piexx.com/index.php?main_page=product_info&cPath=6&products_id=17
The TU-79 tone encoder allows you to add three tone frequencies, out of the 39 standard CTCSS sub audible tones group, to your TR-7950 / TR-7930 transceiver. The TU-79PX tone encoder retains the same physical dimensions as the original TU-79 making installation a breeze. The TU-79PX kit includes the mounting hardware and cables, everything you need for the installation.
If you include the three tone frequencies that you will be using, in the comments section of the order form, we will be happy to ship you tone board set up on these tones.
You can VIEW the Installation Instructions - with photos (before purchase)http://www.piexx.com/tu79/tu79i.html
The other option is Communications Specialists, Inc.http://www.com-spec.com/index1.htm
Top quality California firm that has been supplying CTCSS boards for land mobile (Motorola, GE, Johnson, RCA, Mand amateur radios since the 1970s.
[Product instruction sheets are second web links - below]
SS-64 is an internally (radio) mounted CTCSS ENCODERhttp://www.com-spec.com/ss64.htmhttp://www.com-spec.com/insheet/ss64inst.pdf
TE-32 enternal CTCSS ENCODER boxhttp://www.com-spec.com/te32.htmhttp://www.com-spec.com/insheet/te-32.pdf
IF you also desire CTCSS DECODING (quiet squelch) - then the TS-64 is a very good choice.http://www.com-spec.com/ts64.htmhttp://www.com-spec.com/insheet/ts64inst.pdf
HOOKUP instructions for Kenwood TR-7930 or TR-7950 radio (SS-64)http://www.com-spec.com/insheet/tr7930.pdf