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AN ideal transformer has no wire resistance, but a real one does. Depending upon the wire size and number of turns the winding resistance could be half an ohm or 150 ohms or whatever. (Not limiting discussion to 6v now) Your 6v winding will have very low resistance, but some. Your B+ winding a lot higher. The wire resistance can be thought of as in series with the ideal current source. If it is only .2 ohms, your meter might not detect it, but as we have seen, as little as .43 ohms makes a diference. At least on the 6v.
As to our discussion of applying Ohm's law to your example, we can ignore the wire resistance as we explore the basic concept. But in practical application one should consider transformer wire resistance in calculations. For example, guys going nuts trying to figure out why one of a pair of power tubes always idles a few ma hotter than the other. When they measure the resistance of the output transformer winding they find one side is 75 ohms and the other side 125 ohms. Those resistances are in series with the tubes and the extra 50 ohms affects the current.
That wasn't a power transformer, but consider the B+ winding of a PT. One transformer has a winding resistance of say 150 ohms, and another a resistance of 50 ohms. That extra 100 ohms is in series with the current, so it will have a obvious effect upon sag. Same as putting a 100 ohm resistor in series with your rectifier.
And remember, the transformer doesn;t make current and push it out, the load draws current from it. No load, no current.
Wattage for resistors? As you point out, dissipation is not the limiting factor in many places. How about a 1meg grid return? Essentially zero current, so a 1/100th watt ought to work. But a lot of guys prefer to use 1w resistors in their amps. There are a lot of factors other than dissipation. One is thermal stability. Inherent noise. Another is voltage. A larger resistor may well be able to handle higher voltages. And simple mechanical strength, that can matter in something that vibrates all the time like an amp circuit next to a loud speaker.
As to our discussion of applying Ohm's law to your example, we can ignore the wire resistance as we explore the basic concept. But in practical application one should consider transformer wire resistance in calculations. For example, guys going nuts trying to figure out why one of a pair of power tubes always idles a few ma hotter than the other. When they measure the resistance of the output transformer winding they find one side is 75 ohms and the other side 125 ohms. Those resistances are in series with the tubes and the extra 50 ohms affects the current.
That wasn't a power transformer, but consider the B+ winding of a PT. One transformer has a winding resistance of say 150 ohms, and another a resistance of 50 ohms. That extra 100 ohms is in series with the current, so it will have a obvious effect upon sag. Same as putting a 100 ohm resistor in series with your rectifier.
And remember, the transformer doesn;t make current and push it out, the load draws current from it. No load, no current.
Wattage for resistors? As you point out, dissipation is not the limiting factor in many places. How about a 1meg grid return? Essentially zero current, so a 1/100th watt ought to work. But a lot of guys prefer to use 1w resistors in their amps. There are a lot of factors other than dissipation. One is thermal stability. Inherent noise. Another is voltage. A larger resistor may well be able to handle higher voltages. And simple mechanical strength, that can matter in something that vibrates all the time like an amp circuit next to a loud speaker.
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