Re: 50 Ohm input
If you work out the reactance of a typical 10x passive probe (for a 1M input scope) with (say) 20pF in parallel with 10Meg, the actual loading is mostly down to the capacitance at higher frequencies: At 100MHz the reactance would be about 83 Ohms.
Things only get worse as the frequency increases.
The 10x and 100x "50 Ohm" probes (which function as if an almost pure resistive load with about 1pF additional loading when connected to a 50 Ohm input) actually impose a much lower loading on the circuit than a classic
10x (or even 100x) designed for a 1M input.
So that is why Tektronix chose to fit 50 Ohm inputs to the higher frequency plugins.
PS If you're using a P6202A or a P6201 then they have a power connector (Lemo) that plugs into an outlet on the back of the MF. The original P6202 uses an external mains PSU.
Dave