[ARC5] [Milsurplus] Cold Filament Inrush Current

[Bob kb8tq]

Hi

You also get down to “what tube?” and “made by whom?”. If you dig around a bit, you can
find rectifier tubes that have pretty major inrush currents. (like 8X). No, that’s not the type 
of tube you are going to find in an ARC-5. Some high power transmit tubes are pretty major
inrush devices as well ….

Bob

> On Mar 15, 2018, at 2:06 PM, Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:
> 
> I would think that it would be easy to figure cold-filament in-rush current for any particular 
> tube: 
> 
> 1) measure the filament resistance of the cold tube with a good ohm-meter, 
> 2) use Ohm's law to figure the current at that resistance and the applied voltage, 
> 3) calculate the hot resistance from the published figures for filament voltage and current.
> 4) Extrapolate from those figures.
> 
> For instance the 12SK7's published figures are 12.6 VAC at 0.15 amp, which figures out to 
> 84 ohms.
> 
> I have not measured the cold resistance of a 12SK7's filament, but that should be easy to 
> do.
> 
> So....are those two resistance values different?
> 
> Other factors, of course, are involved: for instance, is the tube a "controlled warm-up" type? 
> Is it a "battery tube"? Etc.
> 
> Ken W7EKB
> 
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