PX4 is not hyped up. It is below the other valves but above the 101D and the 300bs. I can understand someone liking 300b more. The PXs might have a house sound, the 300b is very different (and different from other 300bs on tone, though like other 300bs does not have the dynamics and punch of non 300b valves), and 242 is extremely different. The 45 is just plain boring. I don't have a PX4. I told you PX4 because in your Lampi nothing else - 242, special 45s, PX25s - would work.