[Boatanchors] 120 - 240vac and output

[Vic Rosenthal]

Ron wrote:

> Vic,
> No one will disagree with your example but the point here is that the 4X 
> you calculate is simply due to the fact that 2 Squared is 4.  The 
> specific answer to your specific example is  4. My fear is that your 
> specific example will give everyone the impression that 4X is the 
> general answer when it is not!   The general answer is the square of the 
> current.

Not so.  The voltage drop in the wire is directly proportional to the current, 
E=IR.  That's the first factor of two.  The second factor of two comes from the 
fact that the transformer has to multiply the voltage of the line twice as much 
for the same secondary voltage.  Any example will give the same result as long 
as the relationship of the input voltages is 2:1.   The general answer is the 
square of the ratio between the line voltages!  Remember, all I'm talking about 
is voltage drop due to line resistance, not power.

>  You are correct for your specific example but
> you example becomes really complicated when you start to go further and 
> add the fact that the loading on the secondary is non- linear and then 
> you value of 4 floats all over the place as the voltages and currents 
> settle to the load line of the amplifier current voltage curve. That is 
> specifically why you would work losses using currents and not voltages.

The whole thing started because someone wondered why an amplifier makes less 
power on 120V than 240V.  I responded that, given the same wire size and length 
in the line circuit, the secondary voltage drop due to the line resistance was 
4X greater in the 120V example.  Obviously other things come into play; as you 
point out, the amplifier tube may not be able to draw as much current at a lower 
plate voltage, so the power output will be even less.  And if you install a 
dedicated 240V line, it will probably have an even lower resistance than the 
usual 120V house circuit.

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco