[ARC5] Filaments - How Low Can You Go?

[Gene Smar]

All:

When I built a batt pack for my -25 out of C-cells I salvaged the thin-gauge wire resistor (it's not a real carbon composition resistor) from a dead batt pack and included it in the 3-volt tap off the C cell string. Probably not really necessary in other than arctic battlegrounds, but just in case.....


73 de
Gene Smar AD3F


On 10/19/12, Brooke Clarke<brooke at pacific.net> wrote:

Hi Wayne:

There are a number of considerations.
1) if any power is involved the filament power is about the same as the plate power so reducing the filament voltage 
will have a big impact on the output power.
2) since the lift of a filament (or light bulb) goes as the tenth power of the voltage so a small reduction in voltage 
has a huge impact on lifetime
http://en.wikipedia.org/wiki/Incandescent_light_bulb#Light_output_and_lifetime
3) inrush current is also a consideration. The BA-4386 battery used in the PRC-25 radio has a 1 Ohm resistor in series 
with the filament terminal for this reason..

Have Fun,

Brooke Clarke, N6GCE
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html

Robert Eleazer wrote:
> Here is a stupid question for y'all.
>
> Considering that the overall recommendation is to operate the command receivers with reduced B+, just how low can you go on the voltage for the filaments before you have a problem?
>
> With say, 125V B+ and 12V filament power with a command receiver that has 12V tubes and wired for 24V, how well will it work?
>
> In experiments with my first command set, an R-11A, I was astonished that I could get the B+ down to around 28V and it was still working, if rather faint on the audio output.
>
> Thanks!
>
> Wayne
> WB5WSV
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