[gitarretyp]

All of this pertains to a ps audio hca-2 amp.

I've modded this amp pretty extensively, which included replacing the stock bridge (8A 400V monolithic bridge) with 16 MURS160s in a series configuration. These were in my amp for over a year functioning fine, until i plugged my amp back in after a thunderstorm. When i plugged it in, two of the diodes in seperate legs literally exploded and charred the top of the case. I chalked this up to a power surge of some sort.

To check if it was just the bridge that died, i soldered the stock bridge back into place and everything worked fine. So, i ordered 4 of the 8A 1200V fairchild stealth diodes to make a new bridge. Well, as soon i plugged the amp in, one of these diodes exploded. I have checked, re-checked, checked again, and once more for good measure checked the wiring, and it's fine.

So, my question is what could be causing this? Was the first one a surge and the second simply a faulty diode? Is there something funny about the stealth diodes not handling surges well?

[Dan Banquer]

Did you check the data sheets for surge current?, and the duration of the surge the diode is spec'd for?
                  d.b.

[gitarretyp]

The stealth is spec'd at 100A for halfwave 1 phase 60Hz, the murs at 140A for 8ms, and the stock (kbu8g) is spec'd at 300A with no time given. Maybe that was it, and i should step up to the 15A 600V stealth spec'd at 200A for halfwave 1 phase 60Hz.

[Dan Banquer]

The stealth is spec'd at 100A for halfwave 1 phase 60Hz, the murs at 140A for 8ms, and the stock (kbu8g) is spec'd at 300A with no time given. Maybe that was it, and i should step up to the 15A 600V stealth spec'd at 200A for halfwave 1 phase 60Hz.

Depending on how much capacitance there is in the power supply there can be quite a bit of surge current at turn on. This could well play a major factor in how much "inrush current" those diodes will see. Beefing up the diodes may well help, as well as slowing down the "inrush current".
I use a AC line input filter with chokes in series with the hot and neutral to slow this up. There are other techniques as well.
         Best of Luck;
                   d.b.

[OTL]

So, this design worked successfully for more than a year across many power-ups of the gear?  If so.....

...something downstream has occured that is drawing sufficient current to extingush your diodes, unless of course your current replacement parts don't meet spec, or are significantly different than the original parts used for modification, or one or more of the "surviving" diodes are shorted to some degree.

The old "half split" method applies here.  If possible, remove one channel of draw and test.  Continue to remove/lift components to cut the current circuit in half until the diodes survive.

This method should get you down to less than a dozen components.  Troubleshoot/replace based upon cost vs. time.

One last thought, perhaps replace the entire series chain?

Good luck.

OTL