Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: shark38j on May 29, 2019, 02:48:10 pm
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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
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Are All your tubes in? If not the voltage will be higher.
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Yes tubes are in and I have verified plate voltages
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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!
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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?
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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.
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Everything working now???