[ARC5] 3A5 Filament Voltage Question

[Leslie Smith]

  John,
  I looked at 3 data-sheets for the 3V4 type "tube".
  The last sheet referred to  type 3V4WA, by Tung Sol.
  It described the 3V4WA as "a ruggedized version of the 3V4, making it
  suitable for military operations".
  I know you understand the significance of "W" suffix in the valve type
  designation.
  The datasheet gave a method to test the ability of the "tube" to
  withstand vibration.

  The datasheet says this about the filament:  "Absolute maximum rating
  of the filament voltage (Ef) shall be 1.25 +/- 20% VDC.
  Interestingly it does not give a rating for the series connected
  filament.  Only mentions 1.25 volts in THREE places.
  So (you can do the maths!) 1.25/5 equ 0.25 volts, giving a working
  voltage of 1.0 to 1.5 volts.

  If you want to see the datasheets I have, pls let me know.
  On the other hand, if you don't want to see them, don't tell me, and I
  won't send them.


  73 de Les Smith
  vk2bcu at operamail.com


On Sun, Aug 4, 2013, at 10:18, J. Forster wrote:
> I'm playing with an ART-4 Transmitter. This unit is for reporting the
> blast intensity near an airplaned towed target tube (sock), hence the
> closeness of the shell to target can be estimated.
> 
> Anyway, after tracing the circuit, it has an oscillator and an amplifier
> stage.
> 
> The filament on the 3A5 is parallel wired.
> 
> The spec sheet says 1.4 VDC, Max. A current alkaline battery will put out
> significantly more than that.
> 
> I want to run the thing off an adjustable DC supply, and allow some
> margin.
> 
> Does anyone know roughly what the minimum DC filament voltage to apply
> for
> enough emission to work reasonably well? I just want to test the
> operating
> frequency and get a rough idea of the modulation deviation.
> 
> Thanks,
> 
> -John
> 
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