Including a C- winding on a filament transformer

[AllenB]

The transformer is to have a shielded primary. The secondary, which supplies 2.5V to the filaments will be tapped and connected to a cathode feedback winding on the output transformer.

Will adding a bias voltage winding require more screening or filtration?

 

[kevinkr]

I would use a separate transformer since rectifier switching spikes could appear on the center taped filament winding which is then feed to the cathode winding on the output transformer you mentioned.

In fact to minimize the potential for high frequency cross - talk between the two channels it is probably a good idea to use a separate filament transformer for each channel. (Unless budget or space dictates otherwise in which case you should mention concerns about capacitive coupling between windings, the audio component is common mode to the winding so coupling via mutual inductance should not be a significant issue.)

 

[AllenB]

I hadn't considered using a shared core across channels. Anyway, with hand winding I'm more confident winding them separately.

I guess the bias windings could share a core, or even a winding if regulation was OK. They will be well filtered.Maybe I could share this core with a winding I intend to supply a tertiary output transformer DC flux cancelling winding. It will be needing more current but the source presented to the load will be high impedance, or maybe constant current.