Different 6.3V heaters connections

[CB Amp]

Hello,

For the 6.3V heaters connections, I usually use 2x3.15V windings on my power transformers to balance the voltage, with a mid point connected to ground.
But I often see a simple 6.3V winding, with one tag sometimes connected to the ground, and sometimes not.

What are the differencies, advantages of such circuits ? (except that a simple winding offers a less expensive PT)
When a simple 6.3V winding is not connected to the ground, does it means that it is always internally connected to ground (as some Fender amps) ?

Thanks for your help.

[Phil_S]

Sometimes the filament secondary is tapped in the middle, 3.15-0-3.15, in which case you simply connect the 0 to ground and the 3.15 outer legs to the tube socket(s). The 0 or center tap is a good thing, as it will reduce hum.

Sometimes (and rather common) the filament secondary is 3.15-3.15 (sometimes shown as 6.3-0). In this case, you can choose to run one leg of the winding to the tube socket and ground the other tube pin that supplies the filament, or you can just run one leg to each of the two pins on the socket. The latter is typical in guitar amps, where hum is something we want to avoid by creating an artificial center tap. This involves adding a 100 ohm resistor from each leg to a single ground point.

Either setup is OK. It is probably slightly cheaper to manufacture without the center tap.

[tubetek]

What Phil said is true...
Also, I've seen the power tubes wired (in a push-pull output section) without a center-tap but with one or the other filament lead grounded at the socket. The P-P output section cancels the hum pretty effectively if phased correctly.
The UNIVOX 1061 bass amp I have has 2 6.3 windings; one center-tapped and the other not. The center-tapped winding goes to the preamp tubes and the other goed to the power tubes only with a ground as described above. Hope this helps...
Tom

[jjman]

Some connect the CT to a positive DC source like the cathode of a cathode biased output tube. This is also to reduce hum.

[Andy Le Blanc]

and if your useing a directly heated tube..... the chathode resistor and cap
are connected at the centertap.... Ive seen a couple where a film cap is
connected to ground from the center tap even though the fil. AC is left floating