A simple, macroscale field-emission triode was assembled using a single 3.8 mm diameter Ar+-ion irradiated reticulated vitreous carbon (RVC) cathode. The irradiation process results in random carbon nanostructures on the surface of the RVC, providing effective, low-field emission sites. The use of RVC results in a self-ballasting cathode. The grid electrode further increases local field enhancement on the cathode surface, increasing the extracted current over what is produced in diode mode. The anode electric field required to produce 0.1 mu A/cm(2) was measured to decrease from 0.9 to 0.65 V/mu m with 300 V applied to the grid electrode. With 2.1 V/mu m, and 300 V applied to the grid, the limits of our power supply were reached, and a current density of 16.0 mA/cm(2) and a current of 1.82 mA from a single cathode were measured. Semiconductorlike emission properties, showing three regions of operation, were observed. In region III the cathode emits from a large number of sites, producing a total beam that is readily focused to a small spot size with ordinary electron optics. This low-cost, robust configuration, machined without microfabrication processes or lithography, makes very-high total current in single field-emission triodes possible.