[ARC5] Filaments - How Low Can You Go?

Fri Oct 19 13:11:39 EDT 2012

Yeah..this is always very interesting..I tried an R10A recently (28v 
unmodified) with 15v ac and 150v DC..it worked fine and probably not good 
for the tubes per the present correspondence..I then made up my own version 
of Les's single 24v supply to give 60v B+ and it worked fine..thanks for the 
circuit Les..the general feeling seems to be that the ARC5 receivers are 
very tolerant of variable A and B voltages which is nice to know..73 de 
Pat/EI7CN

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Subject: ARC5 Digest, Vol 105, Issue 96

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Today's Topics:

   1. Re: Filaments - How Low Can You Go? (Kenneth G. Gordon)
   2. Re: Filaments - How Low Can You Go? (Brooke Clarke)
   3. Re: Filaments - How Low Can You Go? (J. Forster)

----------------------------------------------------------------------

Message: 1
Date: Fri, 19 Oct 2012 09:07:40 -0700
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
Subject: Re: [ARC5] Filaments - How Low Can You Go?
To: ARC-5 Mail List <arc5 at mailman.qth.net>
Message-ID: <50817ACC.25907.1FCFB241 at kgordon2006.frontier.com>
Content-Type: text/plain; charset=US-ASCII

On 19 Oct 2012 at 6:58, J. Forster wrote:

> If you're worried about the filament burning out, operate the thing at
> maybe 10% below design voltage. Lifetime is a power law of applied
> voltage. That should lengthen the life a lot, but still maintain
> emission.

Eimac says no more than 5% low....but that is for power tubes.

Ken W7EKB

------------------------------

Message: 2
Date: Fri, 19 Oct 2012 09:22:05 -0700
From: Brooke Clarke <brooke at pacific.net>
Subject: Re: [ARC5] Filaments - How Low Can You Go?
Cc: arc5 at mailman.qth.net
Message-ID: <50817E2D.5060807 at pacific.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

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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------------------------------

Message: 3
Date: Fri, 19 Oct 2012 09:26:22 -0700 (PDT)
From: "J. Forster" <jfor at quikus.com>
Subject: Re: [ARC5] Filaments - How Low Can You Go?
To: kgordon2006 at frontier.com
Cc: ARC-5 Mail List <arc5 at mailman.qth.net>
Message-ID: <50288.12.6.201.2.1350663982.squirrel at popaccts.quikus.com>
Content-Type: text/plain;charset=iso-8859-1

The Diffusion Rate for Solids is explained here:

http://en.wikipedia.org/wiki/Mass_diffusivity

As you can see, the diffusion rate (rate at which surface is repopulated
from the bulk) is strongly dependant on the absolute temperature. This is
a result of Statistical Thermodynamics, verified by experiment.

Best,

-John

===========

> On 19 Oct 2012 at 6:58, J. Forster wrote:
>
>> If you're worried about the filament burning out, operate the thing at
>> maybe 10% below design voltage. Lifetime is a power law of applied
>> voltage. That should lengthen the life a lot, but still maintain
>> emission.
>
> Eimac says no more than 5% low....but that is for power tubes.
>
> Ken W7EKB
> ______________________________________________________________
> ARC5 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/arc5
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:ARC5 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>

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