[ARC5] [Milsurplus] Cold Filament Inrush Current

[Roy Morgan]

Roy sends.

> On Mar 15, 2018, at 5:18 PM, Jack Antonio <scr287 at att.net> wrote:
> 
>> On 3/15/2018 4:28 PM, Michael Clarson wrote:
>> Wasn't the original post about command set rcvrs? These were used in
> 
> I pulled a couple of 12SK7s off the shelf and measured them.
> 
> Setting the supply at 12.6, the first tube initially drew .4A and
> took roughly 5 seconds to come down to .15A.
> 
> The second tube hit .5A, at which point my little
> lab bench supply hits current limit, and came
> down to .15A in 10 seconds.
> 
> I tried a 6SK7, but it severely went into current
> limit at .5A, so would need a beefier supply to
> check that. It came down to .3A in
> about 10 seconds. Probably would have come down
> faster had the supply not gone into current limit.
> 
> I have been poking around BC-348s lately, and 
> 
> Our beloved command sets,  did not bother with that, (filament dropping resistor) and simply
> accept the variations in the source voltage that
> come with a generator/battery system.

It may very well be that aircraft DC systems of the day ran the 24/28 volt buss with the battery connected. This would “regulate” the voltage within moderate limits. 

If I remember correctly, the SH-3 that I flew operated with the battery switch off, and presumably the NiCad battery was under charge by some controlled source. (I could be memory faded on this!). Most equipment ran on 115 (120?) volts from a 3-phase generator.