[Amps] Regulated filament current

[MU 4CX250B]

Bob,
If I understand your question, you want to feed the filament of your
GS35b with a current source, rather than a voltage source. On the face
of it, that seems like an unorthodox thing to do, since the voltage
across the filament will wander around to whatever is necessary to
give the preset current.

I'm not against current-limited filament supplies, which can clamp
startup surge currents to a safe value. If, say, a tube normally
operated at 12 V, you'd set the current limit of the power supply just
above the upper current specification of the tube. At any lower
current, the tube would see a regulated 12 V, and then cross over to a
regulated constant current if the current drawn by the tube ever tried
to exceed the current limit threshold, as would occur when the
filament was cold. Adjustable bench piwer supplies normally have this
cspability.
73,
Jim w8zr

Sent from my iPhone

> On Sep 3, 2015, at 4:40 PM, nemo zilch <nemozilch at gmail.com> wrote:
>
> I am slowly building an amp for hf using a GS35B.  For several reasons I
> decided to feed the filaments with current regulated d.c. I have the
> circuit all designed and it regulates well.  But the question is what
> current should I use?  The spec sheet for the tubes gives a range of
> current to be expected when using the specified 12.6 volts for the
> filaments.  I suppose that there is some variation in filament current draw
> from tube to tube.   My inclination is to adjust the current so that the
> voltage across the tube is 12.6 volts.  Does this seem like the correct
> thing to do?
> Bob W4AOS
>
>
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