We have recently published the design and performance of a 263-GHz traveling wave tube (TWT) amplifier designed for pulse electron paramagnetic resonance (EPR) spectroscopy (Pan et al, 2023). A periodic permanent magnet (PPM) focused pencil beam electron optical system is used. A folded waveguide (FWG) slow wave structure (SWS) with modified serpentine bends is optimized to provide high-power, wideband performance and stable operation. This TWT amplifier provides a maximum 11.9-W saturation output power and 25.5-dB saturation gain. This amplifier has been integrated into a homebuilt 263 GHz quasi-optical bridge EPR spectrometer. We will report pulse EPR performance of this unique high frequency, high power instrument, in particular targeted high spin metals of great interest to bioinorganic chemistry