Astre Systems - Magnet Supply Retrofit

Considerations of
Magnet Supply Retrofit to
Townsend Transmitters

Several variations of magnet supplies were originally installed in Townsend transmitters. Most use a motorized powerstat to control the AC voltage feeding a rectifier bridge and capacitor filter connected to the klystron magnet. In this modification, a new current regulated supply (12" X 10" X 9") is mounted on the interior wall of the cabinet and supplied with three phase 240 VAC. Three new high current semiconductor fuses are supplied in the primary leads to protect the supply from transients. The output of the regulated supply is connected to about 50,000 ufd of filtering and then to the magnet. Existing current meters and shunts often can be used. A control potentiometer is mounted on the front inside door to set the magnet current. The switch controlling powerstat motor, if supplied, is disabled and the powerstat removed. Some variations of Townsend use the magnet current meter relay to control the powerstat motor. In these cases, some wiring changes will be necessary to the control circuitry. The AC circuit breaker supplying the magnet supply will need to be changed. The time required for this modification will be 4-8 hours per cabinet depending on work required due to variations in transmitters.