[AMPS] Filaments vs. Heater??

[measures]

>
>Can someone explain to me the difference between  filament vs. heater? 
>I thought they were one and the same, just diff. nomenclature. 
>
-  Filament:  Tungsten di-carbide emissive coating on Tungsten/Thorium 
core. AKA directly heated cathode. 
- Heater:  Heat source for barium oxide / strontium oxide cathode.  

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