Help - Directly heated AC valves

[Bob Miller]

Hi Simon,
    They used Center tapped fil xfmrs for the DC return and where the AC
would be at a null point.  Same scheme used today for thoriated tungston
fils in trasmitting tubes.

    Bob


Simon Buxton wrote:

> Hi Gang
>
> I notice that in the 1930s quite a number of directly heated valves were
> specified as having AC filaments. Examples include the F443 or 45. Why
> was hum not a problem with these? Was it too low a frequency for the
> speaker or was the filament heavy enough to have sufficient thermal
> inertia for the vairaition to have no effect?
>
> Just wondered.
>
> Simon
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