Help! 5e3 electrolytic capacitor explosion !

[sdlogan9]

Hey guys -

I wired this amp up put in the rectifier tube powered it up and started to take voltages and with in one minute or so the first 16uf blew like a M1000 firecraker!

I am sure it is something super simple, I just dont want to ruin anything when I power it back up.


What should I do first? I have not powered it up since this happened.

[xtian]

Wow! Exciting! Polarity looks correct in your photos...

What voltage(s) did you measure, before the bang?

[JazzGuitarGimp]

A very long time ago, I remember hearing that electrolytics, on rare occasion, are wired backwards at the factory (mismarked). I don’t know if that holds true in this age of total automation, but this could explain why this happened.

Ciao,
Lou

Edit: another possibility is a miswire in the rectifier circuit, if the PT secondary is wired to the first cap, placing AC on it, it will definitely explode. The 100K resistor to the second cap would likely limit its current to the point where it would not explode: at least not immediately.

Edit 2, A shorted rectifier tube would also cause an explosion.

[sdlogan9]

I honestly don't remember exactly what the readings were. -I never really had the time to measure all of the test points

What can I do from here? Can I turn it back on with out frying anything? That is my main concern.

[pompeiisneaks]

It really depends. If you had only the rectifier tube in, it's possible it just slid past the max voltage of 475 of that cap. I built a tweedle dee deluxe (very similar circuit with some dumble tweaks) and after a few power on cycles of testing etc, it blew up too. I can't recall if mine was 450 or 475, but the voltages post rectifier were a lot closer to 500 as I recall. I ended up buying a new cap that was higher rating and that sorted the problem.

~Phil

[pdf64]

The first few powering ups after significant events, eg construction, repairs, service, should be done via a suitable light bulb limiter.
A very low wattage bulb here would have reduced the voltage supplied to the amp.
Or a variac could be used before the limiter to reduce the voltage.
Whatever, just plugging it into the regular outlet opens the door to bad things happening; some degree of mitigation for these seems sensible, good practice.
All that mess will need completely cleaning up, it’s conductive
It looks like there’s a death cap at the fuse holder?

[turbofeedus]

IMO one of many reasons to invest in a variac.
Increasing the AC input slowly allows the caps to form more gently, and very well may have given you indication something is wrong in a way that was more smokey and less explodey.
I grabbed this one off amazon: https://www.amazon.com/YaeCCC-Transform ... 780&sr=8-6
and installed this DMM: https://www.amazon.com/gp/product/B00YY ... UTF8&psc=1

[Masco]

Had a sprague atom internally wired backwards once. I caught it before it poped. I do use a variac AND a light bulb limitter...

[T Wilcox]

Last week while adding a pilot light to an ab763 deluxe build I scooted the chassis sideways forgetting it was balanced on the tube and V3 12at7 got caught and bent the tube socket. quick visual inspection of the tube and it looked fine....I thought
Powered the amp up, checked bias and then started playing. immediately noticed it sounded crappy and then sounded like a little fire cracker went off. Powered down immediately and saw some smoke coming from the V3 socket.. doh
turns out the 12at7 had a small fracture. Even after the pop the tube still had the getter.
found the cathode 25ufd 25v cap blew out and the cathode resistor was burned up. a few minutes passed and I again looked at the tube and the getter was white.

Anyways point of this story is, after letting the smell dissipate for a day or so. I de-soldered the 2 fried components and used paper towels and some q-tips with a little deoxit and wiped out all the splatter from the electrolytic cap exploding. re-soldered in the 2 components and it is like it never happened.
Yours looks like you have a bit more mess but shouldn't be too hard to cleanup

Good luck on the cleanup!