K6XX is using CAT through the mic jack. Do I need to worry about any transistors? I think he did this to isolate the lines.
They are there to convert from RS232 to RS232-TTL. If I recall, the CAT cable has a signal converter in it as well. If you had a small cable adapter, you should be able to plug your CAT cable into and plug into the front of the radio. The same adapter would also have a place to plug in your MIC. If you have the accessory MIC, I think the UP and DOWN buttons don't work. I am testing old memory cells so you would be wise to verify.
Plan on the really cool stuff to disappear over time. While the links here are great, you should be saving the actual pages on your own system. I have stuff that dried up year ago that I can still reference because I kept a copy.
