[AMPS] filament surges

[Rich Measures]

>
>Some of the larger tubes list the maximum surge current for filaments at
>switch on. Has anybody any idea what the limit should be for smaller tubes,
>such as 4CX250B, 4CX1000  etc?
>
>I'd guess at twice nominal operating current as a safe figure, but any
>ideas?
>
For indirectly heated cathode tubes, I have seen no mfg. spec. indicating 
a need to limit heater inrush current.  My guess is that the hot/cold 
resistance ratio in heater type cathodes is much less than that in 
directly heated/thoriated-tungsten cathode tubes.  Typically, 
directly-heated cathodes have a hot/cold res. ratio of 8.3 to 1.  
-  later, Peter.  


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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