[Milsurplus] 3A5 Filament Voltage Question

[J. Forster]

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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