Recently finished the install of the KRX3 receiver and two KSYN3A synthesizers in my K3. I have had the 2nd receiver sitting in its box too long, but family problems was the priority the last year or so. When the new KSYN3a came out, it looked like a good option to install also.
My K3 was a factory assembled unit, so the only opening up of it previously was to install a few optional filters, a simple task. I had read a number of sub-receiver installs on the web, so I knew I was going to have to dig down into the radio a little further.
Fortunately, as I proceeded, the install was smooth. Pulling off and then reinstalling the front panel was simple. Assembling the sub-receiver was pretty simple also. As I got everything ready to start the final effort to install the rather large sub-receiver into the K3, I wondered how I was going to fit it in the space, line up two multi-pin DC/control connectors, push a few coax’s out of the way and line up two holes for the two hold-down screws that go thru the sub- receiver assy. Although this sounds complicated, it really was not, especially if you slightly tilt the sub-receiver toward the front mating dc/control connector and then start lowering it slowly into the space. Elecraft did a good job of getting everything built precisely so that the fit is precise but easily accomplished.