Transformer Voltage Question

[shark38j]

I am working on a project with a Classic Tone #40-18016 power transformer.  This is my first amp project and I expected the rectified voltage to be around ~450V DC.  It seems to be much higher.  As I bring it up on the Variac I reach 400V around 50V AC from mains.  Am I missing something?  I have the two red leads hooked to the bridge rectifier and the center tap floating.  Any information would really be appreciated.

Measured Voltages

Voltage from Variac: 13.4V AC
Voltage out of Transformer: 78V AC
Rectified Voltage: 110V DC

Thanks,
Marc

[davidwpack]

Are All your tubes in? If not the voltage will be higher.

[shark38j]

Yes tubes are in and I have verified plate voltages

[sluckey]

I am working on a project with a Classic Tone #40-18016 power transformer.  This is my first amp project and I expected the rectified voltage to be around ~450V DC.  It seems to be much higher.  As I bring it up on the Variac I reach 400V around 50V AC from mains.  Am I missing something?  I have the two red leads hooked to the bridge rectifier and the center tap floating.  Any information would really be appreciated.

Measured Voltages

Voltage from Variac: 13.4V AC
Voltage out of Transformer: 78V AC
Rectified Voltage: 110V DC

Thanks,
Marc

That transformer will give you in excess of 900V B+ using a bridge rectifier. It was not meant to be used with a bridge. YOU MUST USE A CONVENTIONAL TWO DIODE RECTIFIER WITH THAT PT!

[shark38j]

Ok, my understanding was that 330v - 0 - 330V meant that I would get +330V to -330V from it, 660V P-P.  Your saying that I will get a peak of 660V from it, which is about what I'm getting.  Is there a way to use the center tap to cut it in half?

[sluckey]

Sure. Disconnect the negative terminal of the bridge from ground. LET THE NEGATIVE TERMINAL FLOAT. Then connect the transformer centertap to chassis ground.

Bring it up on a variac and the voltages will be more what you expect.

[sluckey]

Everything working now???