[Amps] A Filament Query

[Radio WC6W]

  A few clarifications on the received replies:

    I presume that it is an oxide coated filament as it operates at barely visible deep red.
 
    I'm not sure if incandescent lamps will correlate as they are run much hotter in normal service.  Running a fine filament incandescent on DC will indeed impact the service life due to filament "notching"
        

  A few additonal data points:

   Operating the filament from a 1V / 35 mA constant current source increases the warm up to 2 seconds.

   The peak inrush from a stiff 1V supply is 100 mA.  The filament current is 32 mA.  Plate current is 300uA.

   Using a 10 ohm ballast R from the 1V supply gives .68 volts and 30 mA at the filament.  Plate current is 250uA. The peak inrush is 40 mA upon shorting the resistor.

   Using a 24 ohm ballast R from the 1V supply gives .5 volts and 25 mA at the filament.  Plate current is 75uA.  The peak inrush is 50 mA upon shorting the resistor.  

   Note that the filament was visually dark in both of the above ballasted situations.

   The above measurements were all taken with 0 grid volts to judge the relative heating of the filament.  The grid would be biased to cutoff in the proposed standby operation.

   The question remains which is the dominant wear mechanism:  Emission or Inrush?

   &

   Thanks for all the input.

   
73 & Good morning,
   Marv WC6W 

http://qsl.net/wc6w/


--- On Thu, 1/13/11, Radio WC6W <wc6w_amps at yahoo.com> wrote:

> From: Radio WC6W <wc6w_amps at yahoo.com>
> Subject: [Amps] A Filament Query
> To: amps at contesting.com
> Date: Thursday, January 13, 2011, 11:22 AM
>     This concerns somewhat
> smaller tubes than are typically discussed on this reflector
> but, where else can I hope to find someone old, errr...
> experienced enough, to know the answer.
> 
>     Given an old miniature tube with a 1 volt
> filament and a (stated) 10,000 hour service life. 
> 
>     And an application that requires the tube to
> be active for slightly less than one second per minute.
> 
>     Is it reasonable to idle the tube with some
> percentage of its rated heater voltage applied, bringing it
> up to full voltage periodically, with the goal of
> substantially increasing its service life?
> 
>     And if so:
>         What percentage of the rated
> heater voltage would be optimal for the "standby" period?
> 
>         How much increase in service
> life may be expected?
> 
>    Note that the directly heated filament
> acheives operating temperature in a fraction of a second
> from a cold start.
> 
> 73 & Good morning,
>    Marv WC6W 
> 
> http://qsl.net/wc6w/
> 
> 
> 
> *
> 
> 
>       
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