[ARC5] [Boatanchors] 3A5 Filament Voltage Question

[Dave Harmon]

Decades ago the 3A5 was one of the tubes used in model airplane radio
control transmitters.
We used 1.5v batteries for the filament and I don't remember any of them
burning out.
Just use a battery and it will last for a looong time.

Dave Harmon
K6XYZ[at]sbcglobal[dot]net
Sperry, Ok.

-----Original Message-----
From: boatanchors-bounces at mailman.qth.net
[mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of J. Forster
Sent: Saturday, August 03, 2013 7:19 PM
To: ARC5 at mailman.QTH.net; boatanchors at mailman.QTH.net;
Milsurplus at mailman.QTH.net
Subject: [Boatanchors] 3A5 Filament Voltage Question

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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