There are a couple of threads on here about this subject already. Here are two of them, a search may reveal more.
Wiring Filaments with Center Tapped Secondaries
Filament transformer center taps
Wiring Filaments with Center Tapped Secondaries
Filament transformer center taps
Standard practice is to use 6VCT transformers and tie the centre tap to ground or a HV reference (for elevating heaters).
That said, I've used 12VCT transformers, and used one "half" of the transformer for left and the other for right. 9/10 times, I use the chassis as ground and wire pairs in series for 12VDC operation though.
That said, I've used 12VCT transformers, and used one "half" of the transformer for left and the other for right. 9/10 times, I use the chassis as ground and wire pairs in series for 12VDC operation though.
^^^^^^^^^ That.
Since tubes work with such high impedances *and* are electrostatically controlled, it´s easy for tube elements (in this case the cathode) to pick induced hum even though interelectrode capacitances are apparently so low (a few pF).
Add that you have "the enemy inside the gates" and 50/60 Hz voltage is thousands of millivolts , compared to feeble a few millivolts Audio being amplified, and you see that Audio grounding filaments (besides DC referencing as mentioned above which of course is needed) is an important precaution.
Since tubes work with such high impedances *and* are electrostatically controlled, it´s easy for tube elements (in this case the cathode) to pick induced hum even though interelectrode capacitances are apparently so low (a few pF).
Add that you have "the enemy inside the gates" and 50/60 Hz voltage is thousands of millivolts , compared to feeble a few millivolts Audio being amplified, and you see that Audio grounding filaments (besides DC referencing as mentioned above which of course is needed) is an important precaution.
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