Comments on a B+ problem?
Posted: July 15th, 2016, 1:30 pm
Hello, all! I am building an amp using a DIYtube ST-70 driver board and tubes/transformers from a Heathkit AA-100 (got the idea here: http://www.diytube.com/phpBB2/viewtopic.php?t=799). I finally got everything powered up and discovered my B+ is 495 V when I would like it to be 430 V. I decided to attempt to fix this by adding 65V worth of Zener diodes between the center tap of the power xformer's secondary winding and ground (got the idea here: http://www.aikenamps.com/index.php/what-is-back-biasing). Here is my schematic:
Because I'm dumb, I didn't consider how this would affect my negative bias supply. It promptly blew the first filter capacitor (C13), I assume from overvoltage. Here is my plan to correct:
1. Make R12 0 ohms
2. Make R11 22.7K ohms (current is so low I think 1W will be ok)
3. Make C13 and C14 220V or more
Any comments on this plan? Is there anything I'm missing?
Because I'm dumb, I didn't consider how this would affect my negative bias supply. It promptly blew the first filter capacitor (C13), I assume from overvoltage. Here is my plan to correct:
1. Make R12 0 ohms
2. Make R11 22.7K ohms (current is so low I think 1W will be ok)
3. Make C13 and C14 220V or more
Any comments on this plan? Is there anything I'm missing?