Resolved: First time build- Blowing fuses

[jgeoffreyharris]

Hi Everyone,

I'm hoping you can help me out or point me to another resource. I recently built a stock Crack unit, and my resistance readings were right on the money. I powered the unit on as instructed- tubes glowed properly, LEDs lit, everything looked good visually. I began testing, and my voltage readings looked good until I got to terminal 20. The probe sparked on 20, and I blew the fuse. Since then, it's blown the fuse immediately upon startup every time. I've double-checked my wiring, cleaned up some of my sloppier solder points and rechecked resistances. Resistances still check out, but I can't get the unit to power on without blowing a fuse. I'm using standard .5A fuses (I don't believe they're fast fuses). Any help is appreciated!

Best,

Joel

[Doc B.]

The probe makes a spark when it hits two terminals at once that are at different potentials, like B+ and ground. My guess would be that you also touched either 19 or 21 when you touched 20 and blew one of the UF4007 rectifiers. With the amp unplugged measure across the leads of each rectifier and look for a very low reading. If one reads very low resistance compared to the other three it is blown.

[jgeoffreyharris]

Thank you so much for the help, Doc! I rechecked my work, and all cap and rectifier orientations were correct. So, after cleaning up some sloppier solder points, I moved up to a 1 amp fuse to see if the unit would power on. I thought I would find some abnormal voltage readings and report back. Turns out everything was right on! I ran the amp for a few hours on the 1A fuse, then moved to a .5A slow blow fuse. Everything sounded great, no problems at all.

I just put in the Speedball kit, and it sounds even better! I'm super-satisfied, and was surprised by how robust and durable the amp actually is. It sounds fantastic despite the fact that I assembled it! Thanks again for all your help!

Best,

Joel

[Doc B.]

Glad you got it sorted out. Congrats!