[Amps] Fil transformer

Geert Jan de Groot pe1hzg at xs4all.nl
Sun Aug 13 08:19:06 EDT 2017

> Just to be clear, I do not require a transformer for providing 
> filament power: it's to fix a design flaw in the Clipperton L, 
> which lacks a centre tap for the filament windings and instead 
> feeds the filaments with RF on one side only, introducing hum. 
> The fix is to parallel a centre-tapped 6v transformer secondary 
> with the filament windings on the main transformer and move 
> the RF input to the new centre tap. 

I'm not sure if any kind of AC transformer is of any help?
The way I have seen this done is that there is an RF choke
between the AC transformer and the filament on both filement wires.
This de-couples the AC and the RF world as it provides a high
impedance to RF signals.

On AC, whether one side, or the middle, is grounded, should not matter
much to RF because the choke provides a high impedance to both
filament wires.

On RF, both filements are floating and isolated by the choke.
A capacitor is used to couple-in the RF to the filament,
both filament wires.

I don't think that your RF input signal passes the center tap of
an AC transformer irrespective of type or taps.


Geert Jan PE1HZG

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