Destructive mistakes

[atmars]

Every once in while, no matter how careful one tries to be, something ends up being wired to the wrong pin or overlooked in some way or another. Most of the time the result is an amp that doesn't function correctly or at all. But, in the reading of posts, every once in awhile is a report of a mistake that results in catastrophe (smoked PT, etc). It would be great if anyone would like to contribute examples of personal or theoretical mishaps that can or do let the magic smoke escape, so myself and others can be forewarned of some of the more expensive mistakes that can be made before we make them.

Thanks

[archaos]

+ 1  :glasses10:

[chocopower]

Once or twice i forget disconnect the discharge wire from B+ to ground when i swicht on the amp after make some mods or measurement.
Lucky me, i ALLWAYS use a bulb limiter for the first swicht on after any work inside a amp.

The funny is that i spent 2-3 minutes searching for the short circuit...

[bluesbear]

NEVER use a 5U4 in an amp designed for 5AR4's or 5Y3's unless you absolutely know for sure the PT can handle 3 amps on the 5v winding. Burn out the 5v winding of a BF Deluxe Reverb one time and you'll never make that mistake again! Sadly, I know!
Dave

[tubeswell]

It would be great if anyone would like to contribute examples of personal or theoretical mishaps that can or do let the magic smoke escape, so myself and others can be forewarned of some of the more expensive mistakes that can be made before we make them.

Um ... don't accidentally short your High Tension/B+ to ground or you'll smoke the PT

[kagliostro]

If you have a CT transformer and CT is connected to ground (if you don't want a doubled voltage)

NEVER use a bridge to rectify (with negative side connected to ground)

use only a pair of single diodes otherwise you burn the transformer and/or the bridge 

Kagliostro

[sluckey]

The first amp I ever built back in the '60s was a Sunn Sonora. It was true PTP and was up and running. I decided to add a power indicator lamp (old Fender style) so I connected it to the end of the filament string. Simple enough. Turned it on and melted the entire filament string together in about 5 seconds. The solder lugs on the lamp socket were shorting together. The filament string was run in a bundle with several other wires and laced up nice and neat with lacing cord just like the Sunn amps. It took a lot longer to rip the bundle apart and rewire than it originally took.   

[tubenit]

First amp I ever worked on was a Gibson Scout for a friend. I did not have a variac so I used a device that controls a router speed thinking it was probably a similar design. Totally smoked the PT in about a minute.

Tubenit

[alerich]

I killed a cheap Sperry multimeter once when I measured B+ one time on my Super Reverb with the meter set for millivolts. I don't miss it much and it was a good excuse to buy my Fluke 111. I have yet to damage any gear or components on my bench. Now, having said that...

[jerrydyer]

Every once in while, no matter how careful one tries to be, something ends up being wired to the wrong pin or overlooked in some way or another. Most of the time the result is an amp that doesn't function correctly or at all. But, in the reading of posts, every once in awhile is a report of a mistake that results in catastrophe (smoked PT, etc). It would be great if anyone would like to contribute examples of personal or theoretical mishaps that can or do let the magic smoke escape, so myself and others can be forewarned of some of the more expensive mistakes that can be made before we make them.

Thanks

 I cant beleive how many bonehead mistakes ive made. Just the other night wanting to swap a 10k into a spot that had a 100k. Grabbed anothe 100k and popped it in there. No change got mad .. went back the next day and realized.   

[HotBluePlates]

Back when I didn't know nuthin, there was an article in a guitar mag about how to transform a blackface bassman into a good rock amp (tweed amps were starting to become expensive, blackface amps were mostly still cheap). One of many changes was to switch from 6L6's to EL34's.

I don't remember if I made a wiring mistake at the sockets, or if the doubling of filament current was to blame, but the instant I switched the power on, the filament wiring got so hot it burned the cloth covering off the filament wires instantly! I shut it off, patched the wires with some heatshrink, and put the 6L6's back in!

Surprisingly, it didn't do anything bad to the filament winding, just burned off the insulation. And to think that was from double-current pulled through the winding.

[Dave]

Wired up a voltage doubler wrong one time. I didn't learn from the mistake though because it burned so badly that I couldn't see what I had done wrong.

Dave

[phsyconoodler]

I wired up a full wave bridge rectifier in a champ build once and it gave a nice 700v that quickly made the filter caps go up in smoke.LOTS of smoke.
  A good test for the smoke alarm.

[andrew_k]

Wired up a voltage quadrupler incorrectly and blew up a 330uF/200V cap in my face.

[RicharD]

This picture shows my biggest electrical mistake.  That is a 45kVA 480V:120/208V 3 phase step down transformer that went KABOOM with me standing 2 ft away.  The culprit was not installation but actually a defective secondary over current device coupled with a primary over current device that had fallen way out of spec over the years.  The secondary breaker had a dead short on the output which had I been paying attention could have easily been found with any old ohm meter.  The 480V breaker was an old FPE breaker which should have tripped long before that center transformer unraveled.  The mistake was not checking everything thoroughly with a meter.  The cause was a defective new piece of gear.  The escalator was worn out old gear.  To put it in perspective, that winding is easily 1/4" in diameter.  Had the cover been off, I would have been severely burned.  I would never ever light up a transformer like that with the cover off.

[Frankenamp]

Buttery:
Glad I haven't had that happen to me, but sumpthin on a smaller scale happened to an electrician buddy of mine who was wiring up a 3 phase, 230V sub panel off another one (daisy chain) Think it was 3/0 wire in a 1.5 or 2" conduit... 'bout 50 or 60 feet down a wall feeding some Molding machines. Well, his helper pulled the cable and was supposed to tie it to the bus bars of the new panel... well lunch came and went... and the helper forgot to finish the job and left the cables tied together (as they were pulled) inside the cabinet. ... ... ... The breaker did it's job just as the cables welded themselves to the inside of the conduit all the way back to the first panel. Much nautical terminology was used in the aftermath.

[Dave]

Yo ho ho!

Dave

[jerrydyer]

how about this, needed to make a speaker cable longer. While my friend watched . cut wires. stripped wires. resoldered wires. with heat shrink.   no extension..   he said "you didnt add any length" 

[jerrydyer]

how about buss wire against the solder tip wondering why solder gun isnt getting hot enough to tin the tip.

[rafe]

I was tapping around the inside of a live amp with the plastic handle of someone elses screwdriver (like a chopstick)
holding the screwdriver by the blade..... I hate to tell this one anyway  ...I got lit up like death row(see my icon) luckily  I was able to toss it acrossed the garage.......the steel went all the way through the handle so you could beat on it or something, like some chisels....that's pretty destructive

[simonallaway]

A friend of mine's first job out of engineering school was working with a guy that built/repaired church organs. One of his first tasks was to wire up solenoids to the wooden stops that controlled the air flow to the different ranks of pipes. They were in fact installing a system that could store presets and with the solenoids, recall them.

Apparently he wired them all the wrong way (something to do with the diodes) and when they turned the system on for the first time, 100 or so wooden stops instantly flew out of the organ fascia and splintered their way to the floor.

(I may be recounting the story incorrectly or embellishing, but you get the gist of it)

[tubesornothing]

Wow you guys sure make a lot of mistakes.  I never make mistakes...

 

[Dave]

Taking test voltage readings, a drop of my sweat fell onto the circuit board of a running Ampeg V4. Zap crackle pop smoke.

Sweat ---- its got electrolytes

Dave

[andrew_k]

Sweat ---- its got electrolytes

Well played.

[Dave]

Thank you. Try the veal.

Dave

[HotBluePlates]

Griping about overseas quality in another thread reminded me of my most destructive mistake. Forgive me for it not being amp-related.

Any, I was working at the Gibson plant, and I was buffing a Les Paul to take out some very minor scratches left over after the guys who do the real buffing were done. They use buffing wheels, which remind you of tires and an axle. The wheel itself is only a little smaller than some tires, and a pair of them are fitted to an axle spun by an electric motor at fairly high RPM.

When you buff a guitar with a lacquer finish, the wheel's cloth is spinning so fast that a good amount of friction is generated, and scratches are literally melted out of the surface. If you stay in one spot a fraction of a second too long or press too hard, you'll burn right through the lacquer down to bare wood.

Did I mention those wheels were spinning really fast? The motor also has a good bit of torque to it. If you bring a squared-off edge to the wheel such that it can catch on the edge, it will burn the lacquer at a minimum. Worst-case, it will snatch the guitar right out of your hands.

Which is exactly what happened to me. I was just about done with the guitar, and was polishing a portion of the headstock when I did a dumb thing and moved the face of the headstock so that the edge was uppermost while the wheel is spinning down towards my feet. The wheel snatched the guitar out of my hands, slammed it to the concrete floor and snapped the neck of a Les Paul clean off at the body.

I swear everyone in the factory stopped what they were doing, and started laughing and clapping! The head of one of the "lines" came over to me and handed me a tag that said "SOLD"... When he saw the look of horror on my face, he added that he was just kidding, but that I would be paying for the next one I broke!

[Tiny_Daddy]

I was assisting a professor with replacing a gas regulator tube in a huge motor-generator control panel filled with mercury rectifiers, thyratrons etc. The idea was to connect a string of zener diodes across the OD3 and reduce the voltage slightly. Well the prof clipped the diodes in with everything running and we were suddenly knee-deep in flames (ball lightning?) The zeners were in pieces on the floor and the motor-generator didn't even grunt. Somehow we lost interest in that project.

[craneclimber]

The mistake was not checking everything thoroughly with a meter.

So easy to do,
So easy to skip.

I would never ever light up a transformer like that with the cover off.

Yes, or stand to the side when you power it up.

[panhead]

I was checking plate voltages on EL34s on an amp last week and one of my wife's pugs jumped at my leg. The meter probe slipped and shorted the plate pin to the filament circuit. Big spark and blown fuse. Replaced the fuse and fired it up again. This time the 5AR4 arced a few times and fizzled out (taking out the fuse again). Replaced the 5AR4 and the fuse after checking the power tranny and all is well. I guess the first zap toasted the recto and the second fire-up finished it off.

[TubeGeek]

I've never had any major amp mistakes....fingers crossed...knock on wood...but I did have an interesting moment while working with Intel.  I was a robotics technician responsible for a toolset that moved silicon semiconductor wafers around with a robotic arm.  During the initial setup of a new machine I was levelling the robot arm and teaching the x, y, z positions and when I finished I loaded up a container full of what I thought were test wafers.  Nope.  Somehow the operators handed me a full lot of production wafers and when I ran the test, the robot positions were not perfect yet...the robot did not save my teachings and 25 wafers shattered before my eyes and 50k was just flushed down the tube. Needless to say I never made that mistake again.

[LooseChange]

Had my share... Live and let learn. Don't want to talk about it. 

[jojokeo]

You all have a great sense of humor. I love reading these and laughed my butt off. Really good idea for a thread, almost theraputic. Dave you are a comedian, panhead's doggy distraction is awesome, HBP's striving for a perfect finish - got one, rafe lighting himself up like a 60's x-mas tree, all really great stuff.  Thanks for sharing and glad no one was seriously or permanently hurt. jerrydyer - I've done exactly the same thing w/ the buss wire as I keep it above my bench on a wooden dowel next to my solder roll and other rolls of wire but the one where you spliced the speaker wires w/ the friend even watching was solid! I want what you two were having. 

I have a number of electrical stories but for me the one that takes the top prize is when while at work, I was asked to check out a problem that was at some batting cages of a local high school. I thought great, I can take some cuts too after I get it up and running and eagerly set about to get over there and fix the issue. It wasn't the newer kind w/ the two wheel's that turn but the old spring loaded arm types. I was rotating the motor & arm assy manually when all of a sudden - WHAM! The arm came down and slammed into the open thumb palm part of my hand, slicing into it down to the bone.  Did I mention that it was spring loaded?!? Luckily I was near a hospital, I had surgery and they fixed me up, and it was my right hand and not my left. After a couple of days  from leaving the hospital w/ a huge wrap on my hand like a giant Q-Tip, I cut away some of wrapping so that I could hold a pick and managed to lightly strum a few chords. It was then I realized I was going to be okay to play again.    I never got the problem at the batting cages fixed and never got to take any swings either, but did get 6 weeks off from work during the middle of summer to hang at the beach so it wasn't all bad.