I had never seen or heard an electrolytic cap explode ..... until this evening. Quite a bang and quite a mess. Metal cap scratched my cheek ..... eye protection saved my eyes ..... but my undies were unprotected ......
Don't forget that eye protection.

Cheers,
Ian

Yep, when they go it's like letting a big clockspring go. Sometimes it can seem like the application personal protective equipment can go overboard but in reality there can never be enough. Bad habits do die hard and I'll admit I don't use goggles as much as I should because that was the doctrine when I entered the workforce. Rather than consider whether something is safe to do or not it was the bad old days of, "your the apprentice, you want to learn a trade, get up that ladder and get at it!", rather than, is the job too high to work from the ladder safely, do I need goggles or earmuffs, do I need someone to foot the ladder, do I need to use a boomlift instead, have I checked the work method statement to see if there is any issue we've forgotten, etc.

Lads who want to become tradesmen or other site workers these days will have their OH&S Whitecard before they leave school now, done as part of the school syllabus. In fact I don't think they can get into a trade course until they have one. Workers certainly won't make it onto a building site without one as it has to be produced when completing induction programmes. So the doctrine of safe work practices is drummed in before they go on the job.

I can't imagine there is a body function I'd rather not lose before my eyesight. It seems like the most important of our senses. For the other problems, there's NappySan.

Rinse in cold water first or you will set the stains in.

I did exaggerate the need for Nappy San ..... but not the bang.

The lesson here is that I never put fingers or hands near the equipment when doing a "gradual power-up" with unfamiliar equipment. If I want to test a circuit at the same time, I do it with pre-attached leads ..... turn on, check multimeter, turn off. Accidentally touching a 'live' component would be highly likely if probibg the circuitry at the same time.

I will be having a good think about how I approached this equipment ..... first change ..... buy a full face mask at Bunnings ....

Cheers,
Ian

Not an uncommon occurrence with swichmode supplies, and even the occasional crossover.
I had a pair of speakers I let a friend borrow only to find out he used them for a thrash metal band!! Sure enough the horns had stopped. But the crossover caps which were now just 2 wires had saved the horns!

the crossover caps which were now just 2 wires

Seem they were very cross over their treatment.

I would point out a couple of things here. It is not always a good idea to "run valves up" using a Variac.
You can poison the cathodes doing that.

There are two things to note with Electrolytics. If they have been left for a long time unused, they will (as they are chemical) loose polarity as the oxide layer that gives them their polarity is eroded.

They then present as a short circuit & can explode. This is one reason for not turning on an old valve radio that has be sitting idle for an indeterminate time.

Secondly, several do not appreciate, nor understand the Silicon Diode & Filament rectifiers. If left unloaded, which is basically the situation with a filament rectifier supplying heater tubes, the voltage will climb to close to twice EMF.

Modern caps rarely give a "Surge" voltage. Most only a working voltage, which one (new) failed to achieve recently & I have had a few 450V ones die quickly also. The safety margin on many now is a dream, as is quality.

On a filament, rectifier supplying heater valves, with 250VDC, I will not use a cap of less than 500V and you will note that most of the old Ducons etc. had a Peak Voltage (PV) or Surge Voltage (SV) of 525V

Marc

I didnt know that about running up on a Variac Marc, good to know!
Josh

Unfortunately with the effluxion of time and evidenced by some articles in a place that should know better. An understanding of the electron tube is being lost. Some things were done with valves, the way they were for good reason.

Marc