I finished my build and decided to fire it up. I measured the DB bias first and these where almost 0 mV, which seemed a bit odd to me. When I measured the power supply voltage I noticed that it measures 1.4 Volts, no matter in which direction I turn the potentiometer (RR3). I verified that the input pin of the LM317 sees the rectified 34 Vdc. I verified that resistors RR1 (121R) and RR2 (2K) are not defective and have the correct values.Checked if the potentiometer is working. It does. All diodes in the voltage supply section are working too and placed in the right direction according to the silk screen.
Some more informations about my build:
In the diamond buffer section I'n using two pairs of 2SC2238/2SA968. As these have a reverse pinout I soldered them to the MOSFET locations according to the image here: http://diyforums.org/MiniMAX/MiniMAXbjt.php
RB8L/R, RB9L/R are jumpered out, hope that I understood that well
Double checked all other transistors and they're all in the right place. For QB1L/R I used J310's instead of PN4392's
I checked the polarity of all caps and they are all positioned the right way.
I'm using a way oversized torroid 24Vac (225VA) transformer. So surely not running out of power here.
Any ideas what might be wrong here?? I'm thinking that it could be a faulty LM317, but maybe anybody has experienced problem this before and knows how to solve it
I have made to little posts here, so I'm not yet allowed to attach any images. Here's a link to a picture of the almost finished board. Please notice that the LM317, tubes and RB14L/R where not yet installed or jumered when I took this picture.
Edited by zwack - 7/17/13 at 12:37am