The piezoelectric transformer (PT) plasma source (PTPS) is a compact radio-frequency-driven plasma source developed for near-space and microspacecraft propulsion. The PTPS utilizes the PT effect to aid in plasma production and acceleration of charged particles to create thrust. Charged-particle emission measured with a Faraday cup and a retarding potential analyzer is presented. Low emitted ion energies are explained by self-bias of the PT output due to charged-particle transfer from the plasma to the PT surface. Finally, self-neutralization of the PTPS was investigated for a PTPS isolated from the vacuum chamber ground.