js22
Active Member
My virst venture into tube audio: an audio generator. Because nothing is as sweet as the sound of a sine wave......
I found a nice article and schematic online.
So far, testing is going well. I disconnected the two 40 uF supply filter caps and tested them for leakage at 400-ish volts. No substantial leaks, so I reconnected them to rectifier, but not to the rest of the circuit. I now have the unit powered on through a variac and plan to let it sit for a while.
The voltmeter is connected to the output of the power supply. So the rectifier is working, the caps haven't exploded, and my hair isn't all pointing straight out. But I have some questions.
1) I brought the variac (gradually) up to about 104 VAC which gave me a DC voltage of 450V. This is the rating of the caps, and also the working voltage of the design. If I plug the unit into the AC outlet directly, I'll be over 450V my a bit. Is this safe? Normally I would *never* run caps at their rated voltage.
2) What to do if I buy new caps? Can I still go with 450V ?
3) Looking ahead, there is a cap in the upper left part of the circuit, 16 uF/150VDC. It's part of the oscillator. It seems to me that if the 6AU6 tube were missing or inoperable, the cap would gradually charge up to the full 450V of the supply; it's simply in series with about 121k ohms. That seems pretty dangerous. Is that just the way it is, or am I missing something?
I found a nice article and schematic online.
So far, testing is going well. I disconnected the two 40 uF supply filter caps and tested them for leakage at 400-ish volts. No substantial leaks, so I reconnected them to rectifier, but not to the rest of the circuit. I now have the unit powered on through a variac and plan to let it sit for a while.
The voltmeter is connected to the output of the power supply. So the rectifier is working, the caps haven't exploded, and my hair isn't all pointing straight out. But I have some questions.
1) I brought the variac (gradually) up to about 104 VAC which gave me a DC voltage of 450V. This is the rating of the caps, and also the working voltage of the design. If I plug the unit into the AC outlet directly, I'll be over 450V my a bit. Is this safe? Normally I would *never* run caps at their rated voltage.
2) What to do if I buy new caps? Can I still go with 450V ?
3) Looking ahead, there is a cap in the upper left part of the circuit, 16 uF/150VDC. It's part of the oscillator. It seems to me that if the 6AU6 tube were missing or inoperable, the cap would gradually charge up to the full 450V of the supply; it's simply in series with about 121k ohms. That seems pretty dangerous. Is that just the way it is, or am I missing something?