Boom! Capacitor down!
So, I started my fire up procedures on my Blackeye 50 Deluxe build - and unfortunately I suffered a catastrophic capacitor failure.
First start up was with the standby off, no tubes in the build. I checked voltages for the switching and DC heaters - running steady at 12v DC. checked voltages out of the secondary to the standby switch...I was getting approximately 350v a side. Which was perfect. Shut the amp down. took a breath.
Then fired back up again. checked voltages again. This time I flipped a switch. Started to check voltages on the rectified voltage. Saw approximately 496. Which was definitely higher than expected, but the amp had no tubes - so without the tube load, I fully expected the PT to put off more stout voltages.
Then I shut off the amp again. Watched the voltages drain off the caps.
Fired up the amp again. Started checking voltages again, but I heard a sound and decided to turn off the amp again. a few seconds later....BANG!!!
C32 blew up ...and when I mean blow up, I mean there was paper and oil everywhere...and the can that used to be the capacitor was sitting next to the PI socket....blown completely out of the board. The axial leads still soldering in, but no cap connected to them.
Obviously, a setback and I wont be deterred.....But Im still scratching my head at this. I started tracing out every connection with my multimeter (which I did before this) and hopefully, I find something I missed. I'm hoping to find something wrong with my wiring, because that will put my mind at ease that a new cap will function OK.
One thing I did notice, was the ground point near the input. Not sure this is related....but do I need to be jumpering the CH lug with the ground point?
Any help or suggestions greatly appreciated!
Frank
Hey Andrea! I figured it out!
Turns out the problem was staring me right in the face! It was my power transformer My PT has the following taps.
Ive build a number of 2xEL34 amps all based on the marshall 2204 power/rectifier platform. So when I sourced this PT, I thought nothing of grabbing a PT with 350v secondaries - especially one that would give me the 14v I need for the switching....because I always use PTs with 350v secondaries for these amps.
So I just wired it up without realizing your schematic and layout was designed for a PT with 180V secondaries and a voltage doubling circuit in the rectifier (which is similar to what's going on in the 2203 power section - an amp Ive never built). The HV secondary center tap going in between the two 100uf capacitors was doubling the voltage on the B+ rail. C34/C35 held up, because I think the fact that they were tied in series increased their power handling...but the very next filter cap in line was C32....and thats why it exploded....and thats why fuses were popping when I had tubes in the amp.
So I pulled the center tap from in-between C34/C35 and temporarily tied it to ground....and as soon as I did that, voltages on C34/C35 went right down to 485v!!!!
So I did a little rewiring of the rectifier circuit....I went to a 4 diode center tap rectifier like in the 2204, I soldered the HV center tap to ground and I bridged the positive sides of C34 & C35 to use single 100uf 500v filter cap in C34 (my actual Friedman BE50 has a single 100uf in this location).
The amp immediately came to life. After my usual start up testing, I put in the good tubes I had planned for this amp - and Im happy to report that it sounds just like my actual BE50.
I'll post some pics in a new thread in the other section. But I wanted to thank you for your help and guidance throughout this entire process. Even though I had this issue with the power transformer, the circuit board made this build SO MUCH easier.
I am VERY tempted to put together a Deluxe Reverb next.