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The use of four-gap double-ended thyratrons in a 30- to 100-µs pulse modulator is described. The PFN-type modulator operates at 105-kV peak, charged from the 11-kV public supply, and powers an ill-matched and potentially unreliable load directly at 30 to 70 kV without a pulse transformer. The maximum repetition rate is 200 pps. The completed modulator has been delivered to the customer and successfully recommissioned. Satisfactory operation is reported with 200-MW 6-kJ pulses in bursts of average power up to 400 kW; this is well in excess of the published ratings of the tubes employed. The methods used to obtain this performance are discussed and the main details are given of pulse discharge, energy dump, and switched charge circuits appropriate to the thyratrons used. The possibility of uprating the modulator is mentioned, and certain recent developments in large thyratrons are discussed. These include a new pentode-type electrode system which should give improved performance with simpler deck circuitry. For extended bursts at long pulse lengths the realistic maximum capability of single tubes in current production seems to be about 1-GW peak at 2-MW average power.