A high-power vacuum electron device source of 10 mm-0.1 mm wavelength radiation is composed of an electron gun joined to a RF vacuum electronic circuit. The electron gun includes a cathode, a focus electrode, and a grid. It generates an electron beam that is injected into the circuit for amplifying RF waves. The circuit is composed of metal circuit plates, e.g., copper alloy, that mate with each other and are shaped to provide a beam tunnel and RF circuit envelopes. Precision alignment pins made of nickel super alloy, are used to mutually align the metal circuit plates using elastic averaging implemented by positioning the precision alignment pins in precision alignment holes in the metal circuit plates. Preferably, the electron gun is aligned with the circuit using quasi-kinematic coupling.