A maximal electron current in a neutralized electron beam is constrained by the beam-drift instability of the primary electrons and the neutralizing ions. To suppress this instability and to increase the threshold of the electron current, the active methods are usually used. As a result of the application of these methods the spectrum of neutralizing ions is changed. The measurement of the ion mass spectrum is performed with the special ion mass analyzer. The experiments on the JINR test bench show that the presence of light ions (hydrogen) in the beam decreases the threshold beam current related to the beam-drift instability.