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Pulse transformers suitable for high-frequency and high-voltage operations in a traveling-wave tube amplifier (TWTA) had been designed, fabricated, and tested. Two transformers with different operation frequency of 100 and 80 kHz were designed, fabricated, and tested. The transformer with 100-kHz switching frequency had input and output voltages of 250 Vdc and -4.1 kV, respectively. Operating power was 3.06 kW. Achieved power density of the 100-kHz transformers was 22.26 W/cm3. The transformer with 80-kHz switching frequency had input and output voltages of 265 Vdc and -4.1 kV, respectively. Normal operating power of the transformer was 1.67 kW. Achieved power density of the 80-kHz transformer was 12.15 W/cm3. Three different winding arrangements for the 80-kHz transformer were tested and it was found that the one with a sandwiched primary between secondary windings had the best performance in electrical characteristics. It was possible to reduce the stray capacitance while maintaining low-leakage inductance with the best arrangement. Therefore, the self-resonant frequency was far separated from the operating frequency, and, thus, the new arrangement minimized the self-resonant current that is generally one of source for transformer temperature rise.