Power supply help!

[gary f]

Simple question I guess

I'm building this circuit to supply plates for my amp at 315 and 305 volt. Main transfo is 275-0-275 volt.

Right now, in theory, I should get less than 300 volt at point A and B, but I get 420 volt approximately. WHY?

I should have maybe 250 volt. Am I correct?

Thank you
F

 

[wa2ise]

If there isn't enough of a load, the voltage will be higher. With no load, the filter caps will eventually charge up to 275 times 1.414 volts, about 385V for a powerline at 120V, but if your powerline is a little higher, and the 275-0-275V secondary is its voltage under load, these two factors would put the unloaded output voltage even higher to the 420V you're seeing.

 

[gary f]

There is no load right now...

Did not thought that this could cause a problem....
Thanks

Should I put my tubes in and try?
F

 

[gary f]

And my power line is 125 volt AC. Very interresting
F

 

[Rtop84]

Did you measured it without load?

 

[gary f]

Yes I did. No load.

Is that bad??

F

 

[Rtop84]

Yes. Absence of load causes higher voltage.If you convinced that your amp is good you can, but better solution is putting high power resistor.

 

[Sheldon]

http://www.duncanamps.com/psud2/

PSUD is your friend. It's free, it's easy, it works.

Sheldon

 

[lndm]

Is your transformer an old one that would have given 275/0/275 back when mains voltage was lower? Your result does not seem surprising. The resistor will develop a voltage drop only after there is current running through it. Connect your amp and the rails should come right down.

 

[Sherman]

And my power line is 125 volt AC. Very interresting
F

You should also try measuring the AC voltage with a true RMS meter. I believe you'll then find your AC mains at 120V or less.