Doped fiber optical amplifiers play a vital role in telecommunication systems. Their operation is enabled by the interaction of pump light and dopants within the fiber, which convert optical power to a higher wavelength. The typical implementation involves pumping a doped fiber core with an intense pump laser, thus amplifying a weaker input signal at a different wavelength. Achieving high output signal power, correspondingly, requires a high-powered pump laser. One of the methods for achieving higher output signal power is cladding-pumping, where a multimode pump source is used. While this results in lower pump absorption, it may have optical output power an order of magnitude higher than a conventional core-pumping source, reaching several watts, which easily offsets the weaker pump absorption. We present an experimental characterization of the gain profile evolution of a multi-channel signal propagating through an increasing length of double-clad Er3+/Yb3+-co-doped fiber. The test signal consists of 48 channels of equal power in the optical C-band spaced 100 GHz apart, where the per-channel input power is set between -27 and -10 dBm, while varying the pump source power between 0.6 and 2.0 W. The primary findings include the wavelength-dependent gain profile pivoting around the gain peaks as a function of doped fiber length, with longer wavelengths experiencing increasingly higher gain. Similarly, higher input signal power results in a higher proportion of the total output power going towards longer wavelengths. Simultaneously, despite the relatively low pump absorption, with the pump power levels involved, it is very possible to reach signal gain saturation at low signal powers typical for long-haul dense wavelength division multiplexing transmission systems.