Suspended Cathode Module (with Integrated Heater)

The Cathode Module is a suspended cathode with an integral heater.

The suspended construction offers several advantages:

• Low power
• Fast switch on
• Good thermal stability
• Low white balance drift in colour TV applications

The integrated heater offers several advantages:

• Reduces complexity at gun assembly
• Reduces the variation in cathode temperature
• Easier assembly into electron guns since no heater assembly is required

Cathodes available in this construction:

Oxide, Cermet and Impregnated.

Suspended Cathode

The Cathode Module is a suspended cathode designed to be mounted in circular eyelets in electron guns. The suspended construction offers several advantages over non-suspended cathodes where the cap is directly attached to the supporting bush:

• Low power
• Fast switch on
• Good thermal stability
• Low white balance drift in colour TV applications

Suspended cathodes are available in different sizes depending on the application. Please contact us for more details.

A separate heater is inserted during the gun assembly process to deliver the correct cathode temperature. The heater required depends on the heater connections (series or parallel) the method of mounting (on a bracket or directly welded) and the dimensions of the cathode bush.

Please contact us for details of different heater and cathode combinations available.

Advantages of Suspended Cathode

The suspended cathode structure has several advantages over a non-suspended structure.

• A fast warm up time
• No change in cathode height at switch on
• Very fast time to achieve stable white balance point

The high thermal efficiency gives a Fast Warm Up Time as below graph shows.

Typically, the suspended cathode reaches its maximum emission in about 7 seconds compared to 13 seconds for a non-suspended cathode.

The high thermal efficiency also gives a very stable construction.

In the following graph, the suspended cathode construction reaches a stable temperature more quickly than a non-suspended cathode. The suspension tapes are designed to compensate for the thermal expansion of the cathode. For a non-suspended cathode, the cathode-grid 1 distance changes by up to 20 microns over the first 15 minutes after applying a heater voltage. For a suspended cathode, the cathode-grid 1 distance does not change when a heater voltage is applied.

In a colour picture tube (CPT) or colour data tube (CDT) the suspended cathode structure also improves the white-balance drift.

The above graph shows the difference in cathode current between the red, green and blue cathodes of a colour picture tube (CPT). The suspended cathode stabilises in ~ 3 minutes after switch on from cold while the non-suspended cathode can take 15 minutes to stabilise.