Calculations to determine the speed and intensity of the destruction of any device via electricity must involve the resistance / impedance of the current source, the stored energy that it contains, and the resistance / impedance of the device being "tested." Yes, a vacuum tube can explode rather violently under certain conditions.
I have an old HP6448B power supply for working on big tube amps. It is rated for 600 volts (turned up to 650) at 1.5 Amps (turned up to 1.7). It is an old style 60 Hz switcher which is slow. The current limiter takes nearly a second to kick in and there is 1000 uF of capacitance directly across the output inside the supply. A dead short across the output will produce a BIG BANG and any small component in its path will simply disappear. An arc from a resistor to the ground plating below it on a PC board blew a hole through the board. If an arc occurs in a vacuum tube with little other resistance in the path this supply will make it explode. This supply scattered two 6HJ5's all over my workspace. An early (1990's) poorly constructed Chinese KT88 shattered all by itself in an otherwise working guitar amp due to an internal short caused by the vibrations from the speaker.
An attempt to quantify or predict the possible outcomes of a failure mode like these is an exercise in frustration since there are too many unknown variables. All experimentation along these lines should be undertaken in a safe manner with good eye (an other) protection. I have blown up a lot of otherwise useless electronic components just because I can. About 40 years ago I bought a big box full of 470 uF 50 volt capacitors for a DIY project, but they were old and of poor quality, so most of them were "tested" by plugging them in to the US 120 volt power outlet on the other end of a 50 foot extension cord. Many of them simply exploded immediately on power up but some just went open or vented. There was a huge variability in the reaction to this abuse that can not be predicted since no two capacitors are exactly the same. These had 1971 dates on them so modern low ESR capacitors are likely more uniform.
I've been involved in the space industry before, and the rule of thumb is take a commercially reasonable price and put three or four zeros afterwards.
True, the BOM is scary, but the part specifications are quite extensive: accuracy, temperature, pressure, decompression, humidity, mechanical/electrical shock, etc.. To blow up such a part, as I did, took some very expensive test equipment, a faulty manufacturing process and a very tired engineer.
Hey, I remember those.... we used to have them all over the metrology labs in Southern Cal - when we used to have an actual aerospace industry before the nuts in Sacramento ran it out of town...
How about the HPIB programmable power supplies, eh? Those are the ones we had in the ATE station I used to blow up my board. Big rack mounted power supplies... seven racks of instruments with an scanner interface adapter for the ITA. We used to write TPS with ATLAS/Fortran in an HP1000F.
Those were the days.... work all day with that HP stuff, party most of the night and somehow squeeze a nap, a shower and a toothbrush in there...
Got Up
Got out of bed
Took a shower'n combed my head
On the way downstairs
To program stuff with HP-IB
I grabbed some expresso
And went into a dream...
Aaaah..
Watch the caps blow up
The diodes burst in flame
And the safety guys
Will bury me under paper and pen...
It turns out that those test stations had a reset button. The way it worked was to latch all of the commanded voltage bits to ONE and then reset them to zero. As you can imagine, the Einsteins that designed that didn't think that would create a huge SPIKE on the output of ALL power supplies.
I believe I was the first (and only) one ever to try the Big Red Reset Button. No one at the USAF depots ever used it, I guess. It did quite a bit of damage.
Last edited:
D
Deleted member 550749
I have been known to get frustrated with some of my projects that will not function as expected. I built a little guitar amp that used tubes from a common AA% table radio. After trying everything I can think of to make it work several times, I gave up and jut turned the power supply all the way up feeding 400 volts into a circuit that expected about 120 volts. The maximum plate voltage spec for the 50C5 tubes was around 120 volts. I was expecting death by power supply hoping to see the little proto board fry into a useless pile of junk which would go in the trash. I was quite surprised to see it live and scream out some real nice overdriven tones. I backed the voltage down to 340 where nothing was glowing and it still sounded good. That was several years ago and that test board still works and has provides the info needed for a successful 20 watt amp design. The Phoenix board that rose from the fire successfully passed the full power (20 watts) continuously for 12 hours test with no blown parts or degradation in performance.
There is something very wrong the way she's handling that tool.
Is that a soldering iron of some sort?
And, who handled PC boards like that nowadays... anyhow?
Reminds of the day, back in the 80s, when they need some pictures of our lab for the company magazine and investor newsletter.
So they asked us to set up one of the test stations and they took pictures of our team. Nice! We thought... all of our hard work and we will be acknowledged.
But after our pictures they went and brought in a guy from marketing and a woman from HR. Gave them white lab coats and goggles and posed them handling some hardware. Well, we were mighty pissed off... so, this is what we did, we set him up poking an expensive looking RF board with NO ESD wrist strap... AND... we set her up handling the HP1980B scope which was obviously set up in self test with a 1KHz signal. I mean, you could see his hands touching expensive hardware (it was actually a prop)... and the scope's lead was obviously clipped to the test signal post... and set on AUTO TEST....
Every engineer, technician and manufacturing person in the company knew that.. and if they didn't, they found out. That was one very famous issue of the company newsletter: I figure the ESD trainers must have used that picture for years: How Not To Do It.
I mean, we even wore shirts and ties for out team picture. Pfff!...
Is that a soldering iron of some sort?
And, who handled PC boards like that nowadays... anyhow?
Reminds of the day, back in the 80s, when they need some pictures of our lab for the company magazine and investor newsletter.
So they asked us to set up one of the test stations and they took pictures of our team. Nice! We thought... all of our hard work and we will be acknowledged.
But after our pictures they went and brought in a guy from marketing and a woman from HR. Gave them white lab coats and goggles and posed them handling some hardware. Well, we were mighty pissed off... so, this is what we did, we set him up poking an expensive looking RF board with NO ESD wrist strap... AND... we set her up handling the HP1980B scope which was obviously set up in self test with a 1KHz signal. I mean, you could see his hands touching expensive hardware (it was actually a prop)... and the scope's lead was obviously clipped to the test signal post... and set on AUTO TEST....
Every engineer, technician and manufacturing person in the company knew that.. and if they didn't, they found out. That was one very famous issue of the company newsletter: I figure the ESD trainers must have used that picture for years: How Not To Do It.
I mean, we even wore shirts and ties for out team picture. Pfff!...