Help - Directly heated AC valves

[Jan Axing]

You got rid of the hum by either grounding a center tap on the
filament winding or by connecting a low ohmic rheostat to the
filament with the viper grounded. This was adjusted for minimum hum.

Jan, SM5GNN

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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