• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

calculating total current draw

Hi all,

Could someone check this out for me - I think I must be wrong.

I have an amp that uses 4 6L6, 2 6FQ7 and 1 12AT7. All valves are 6.3V and the total current draw for them all is 3.6+1.2+0.6= 5.4A at 6.3V.

Now I want to roughly figure out what current this amp will draw from the mains supply. A quick calculation on ohms law says that that equals 34W. Now I know the B+ and various other bits and pieces will add a bit more, but the plate on the back of this amp says 250W. Fuse fitted is 4A.

Whats the correct way of getting a reasonably close estimate on this?