In the continuing saga of this 100 watt build using a Weber chassis and PT, I have a problem with extremely high DC. It started when I first turned on the standby switch without realizing that I had mistakenly used a 5.6K instead of a 56K as a balance resistor on the screen supply caps. To clarify, I installed one 56K and one 5.6K. It immediately smelled hot and I measured something like 700Vdc one on of the screen caps. I shut if off at once and that's when I noticed my error. Both resistors were burned of course, but it did not blow a fuse. i was out of 56K 2W mo's, so I used 100K's instead as recommended in the Wiki article on bleeder resistors.
I checked the PT voltages and with 120Vac in using the Variac, which I should have done the first time but didn't, I measured 362Vac on the HT taps. Nothing looks burned or smells like it was burned so I don;t think I damaged anything. I then removed the HT fuse and set the input voltage at 50.2. That is the closest I could get to a round number. I got the following readings which I have noted on the JPEG below.
50.2 volts in was as high as I dared go without going overvoltage on the caps again. Any help would be greatly appreciated. I forgot to mention that I have gone over the wiring three times using the SLP-XL schematic, and everything is correct.
Here is a link to a high-res photo of the work: http://i169.photobucket.com/albums/u217 ... f0a48f.jpg
Thank you everyone
Ivabiggun
HT very high post rectifier
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HT very high post rectifier
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Re: HT very high post rectifier
You used a bridge rectifier,that is wrong!!
Use 2 diode 's on the outher taps and the center tap is ground.
Now you have a voltage doubler witch explain the 700volt +
Or use the right transformer 2x 180volt centertap
Erik
Use 2 diode 's on the outher taps and the center tap is ground.
Now you have a voltage doubler witch explain the 700volt +
Or use the right transformer 2x 180volt centertap
Erik
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Re: HT very high post rectifier
Hi Erik, thank you for the reply. I am building this for someone and they do not want to buy another PT. It never occurred to me that I could not wire this as a voltage doubler. If you look at the Weber schematic it uses one on his Copper Caps which are supposed to emulate a tube rectifier.
Oh well, we learn by doing.
It was doubling 350 volts, no wonder it was so high. Today's lesson is: "Don't be in a hurry and use your Variac."
Thank you for the help.
Ivabiggun
I suppose I should redo it as a full-wave center tap like the 1987 circuit. Three of the caps are leaking DC so I will have to replace those. ![Embarassed :oops:](./images/smilies/icon_redface.gif)
![Laughing :lol:](./images/smilies/icon_lol.gif)
Thank you for the help.
Ivabiggun
"Sign zee papers, old man"