A reception unit for a magnetic resonance tomography apparatus has an RF preamplifier connected at its signal input to a local coil with a PIN diode connected in parallel with the signal input and a supply voltage connection of the RF preamplifier being connected to a direct voltage source. The reception unit has a supply node that is connected with the supply voltage connection, the PIN diode and a cross-over switch for alternating connection of the supply node to the direct voltage source or a direct current source.