The reason for recommending regulated DC for the filaments is that in my experience some of the concerns like stable filament voltage from a low transformer or biasing to minimize hum, are no longer a problem with DC filaments. You don't have to bias DC filaments to reduce leakage hum, because it doesn't exist.
However if you do stick with AC the voltage might be near the ideal 6.3V if the transformer isn't 100% loaded. Since your rectifier tube can handle 500V from cathode to filament, I don't see why you can't use one half of your 6-0-6V to power the rectifier. But, if you do get too much hum with the CT connected to ground, biasing might get a little tricky with the common connection, because there will be some leakage from the rectifier cathode, and that noise is not a nice sinewave. It will couple through the transformer secondary to your audio tubes.
However if you do stick with AC the voltage might be near the ideal 6.3V if the transformer isn't 100% loaded. Since your rectifier tube can handle 500V from cathode to filament, I don't see why you can't use one half of your 6-0-6V to power the rectifier. But, if you do get too much hum with the CT connected to ground, biasing might get a little tricky with the common connection, because there will be some leakage from the rectifier cathode, and that noise is not a nice sinewave. It will couple through the transformer secondary to your audio tubes.
Thanks guys for the advice. 
So I'll bias the heater on the amplifier tube as described and leave the heater on the rectifier alone.
Do I have to connect the CT to ground?
The transformer is 24VA, so 4A at 6V. The EZ81 needs 1A, the 6H30 needs 0.85A. The mains here seems to always stay above the rated 230V, so I think I should be getting above 6V fine.
If I have to, I can also get a separate transformer for each tube, or even go DC.
So I'll bias the heater on the amplifier tube as described and leave the heater on the rectifier alone.
Do I have to connect the CT to ground?
The transformer is 24VA, so 4A at 6V. The EZ81 needs 1A, the 6H30 needs 0.85A. The mains here seems to always stay above the rated 230V, so I think I should be getting above 6V fine.
If I have to, I can also get a separate transformer for each tube, or even go DC.
One of us is confused. You have a single secondary winding, giving 6-0-6V. You intend using one half of the winding to power the signal valve heater, and the other half to power the rectifier heater. Therefore whatever bias you put on it will necessarily apply to both valves. You can't make an independent choice.Navyblue said:
You have to connect the winding to something, as a heater circuit must always have a voltage reference. The simplest option is to ground the CT. This is also the best way of reducing any capacitive feedthrough from the rectifier cathode to the signal cathode.
Why does such a simple issue get so complicated?
Please pardon me if this seems rudimentary to you. This is the part that I don't understand. When the heater is biased, and then grounded, wouldn't it get unbiased?
I think you are overestimating me.
As I said earlier, I am new with this thing.- Status
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