Knut, you should have the KXV3 (or KXV3A option in your K3 to use the PR6. The order page on the Elecraft website reads: "PR6 Low Noise 6m GaAs FET Preamp (0.5 dB typ) for the K3 and most other rigs (Connects to the RX IN/OUT conn. on the KXV3.)" 73, Bruce, N1RX