[ARC5] [Milsurplus] Cold Filament Inrush Current

[DSP3]

One of the factors mentioned in the Eimac power tube book is to address 
in-rush by ensuring that the filament transformer (especially in 
thoriated tungsten types) is rated for the actual current of the tubes, 
and no more.  That way the lower, in-rush resistance it initially 
mitigated by sag in the transformer.  The opposite scenario is that an 
overrated transformer will sink whatever current necessary during the 
cold, heat-up period.  I have seen tubes "bloom" when power is applied 
where the extra current is available.  Not a good situation...

Jeep - K3HVG


On 3/15/2018 2:37 PM, Tom Lee wrote:
> Exactly. Resistance is a function of temperature, so tubes that 
> operate at white-hot incandescence (pure tungsten) will have a larger 
> hot-to-cold resistance ratio than oxide-cathode tubes. For the former, 
> a 5:1 ratio is not uncommon, where for the latter, something around 
> 2:1 is more typical.
>
> --Tom
>

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