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DIY Disasters

Nov 25, 2017 at 10:20 PM Thread Starter Post #1 of 15
mourip

mourip

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I have had several experiences with my own equipment and one with a friend's that resulted in either an explosion(small), smoke, and\or burning. I have been doing DIY for about 35 years and have never had a serious fire but have received a couple of bad shocks. I thought that I would start a thread regarding DIY to see if others have cautionary tales to share.

I will go first...

Shocks: In the early days of building tube amps and modifying them I had two episodes that gave me a profound respect for high voltage. Once I was working on the underside of an FM receiver that was powered on and my tool slipped causing a short. That event kicked me out of my chair and the "hot" chassis dropped to the floor, luckily not on me. Another time I just spaced out and touched a bare 400 volt wire. That put a hole in my finger. In the last 30 years I have been much more cautious.

Letting the smoke out: I once had a Dynaco MkIII resistor burn up. Luckily I heard a pop and turned around to see it burning so that I could power it off. Another time I had built a small Tripath amp which was battery powered. In the process of plugging in a switchable battery charger into the cheap rear panel socket I bent the center pin against the ground sleeve. The battery saw a dead short and poured its heart out melting the internal wiring and filling the room with acrid smoke. The amp and battery were OK but the house smelled pretty bad. In the case of my friend, her 2A3 amp had a solid state heater rectifier which decided to die. This short overheated the power transformer and basically melted it. It was replaced and a smaller value fuse installed as the original one never popped!

Take home lessons:

1. Never leave tube equipment on when you are not home or nearby.
2. Always use fuses of the correct value and definitely use one.
3. When testing voltages, especially in tight spaces use probes with clips/hooks. Keep one had in your pocket.
4. Always over specify DIY parts. Don't use old capacitors. When they blow it can be pretty exciting.
5. Always check power wiring multiple times when connecting it up.
6. Use a shorting resistor to discharge power supply capacitors on a powered off amp. They can carry charge for a long time.

Let's share our disaster stories and safety tips. It could save a life or a home...
 
Nov 28, 2017 at 12:24 PM Post #3 of 15
All the rules above are super important, thanks for sharing! I personally like to have another person around when I power up a high voltage amp for the first time for testing.

A few more:
Fuse the hot, not the neutral
Don't power cycle a tube amplifier too quickly
A properly grounded chassis is essential
 
Nov 28, 2017 at 12:50 PM Post #4 of 15
Disaster ? The worse scenarios can kill you, but DIY is where the fun is at, for my own opinion because I love DIY :D

Definitely blowing Capacitors are so much fun Just as much as the disaster
 
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Dec 1, 2017 at 7:28 AM Post #5 of 15
I apologize, but I'm still stuck on this: "Once I was working on the underside of an FM receiver that was powered on ..."

The absolute, number one rule when working on something electrical is to make certain the power is OFF. In industry, there are significant procedures and often built-in mechanisms to ensure that power is off when working on lethal voltages. This collection of procedures/mechanisms is referred to as "lock-out/tag-out." It means just what it says: physical, keyed locks are used to prevent anyone from powering a circuit and clearly visible tags are also used to mark the switch/breaker.

That's not practical when working on our electronics-based devices, but making sure the unit is turned off and not plugged in is a minimum precaution. I especially don't agree with this 'one hand behind the back' (or pocket) stuff. That's admitting you're playing Russian roulette from the outset. Are you willing to bet your life on keeping a hand behind your back?

If you have to measure something with potentially lethal voltage (that includes line power), then figure out how to use clamps or something similar with your meter. Attach them prior to turning the device on. Power it up without touching anything, note the meter reading, then turn it off and unplug it.
 
Dec 1, 2017 at 4:37 PM Post #6 of 15
"If you have to measure something with potentially lethal voltage (that includes line power), then figure out how to use clamps or something similar with your meter. Attach them prior to turning the device on. Power it up without touching anything, note the meter reading, then turn it off and unplug it."

I would certainly agree and this was one of the events that prompted me to start the thread. I pointed out what might happen if you did it the wrong way but neglected to explain how to do it properly.

Thanks.
 
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Jun 5, 2018 at 7:20 PM Post #10 of 15
When opening up old vintage stuff, especially if there's plastic involved, be very careful as it can become brittle (or maybe was just brittle and under-speced to start with).

Found this out when I was opening up a 1970s-ish vintage pair of Stax SR-3s and almost immediately broke some of the screw holes off. I still have the drivers but haven't figured out anything viable yet for a replacement enclosure. First attempt was an aperiodic (semi-closed) pair of ear cups made using some sound isolating headphones with melamine foam and velour cloth over a vent hole for damping, but they sounded awful. Definitely not up to the original Stax reputation, although that just might have been some hubris on my part to assume I would get that right on the first try.
 
Jun 29, 2018 at 7:51 AM Post #11 of 15
altie said:
When opening up old vintage stuff, especially if there's plastic involved, be very careful as it can become brittle (or maybe was just brittle and under-speced to start with).

Found this out when I was opening up a 1970s-ish vintage pair of Stax SR-3s and almost immediately broke some of the screw holes off. I still have the drivers but haven't figured out anything viable yet for a replacement enclosure. First attempt was an aperiodic (semi-closed) pair of ear cups made using some sound isolating headphones with melamine foam and velour cloth over a vent hole for damping, but they sounded awful. Definitely not up to the original Stax reputation, although that just might have been some hubris on my part to assume I would get that right on the first try.
Click to expand...

I poke around a little and have found that old plastic almost always becomes brittle. The only difference seems to be to what degree. I looked it uponce and it's apparently from the platicisers outgassing, or something along those lines. Always handle with care.
 
Jul 9, 2018 at 12:12 PM Post #12 of 15
Quasimodosbelfry said:
I poke around a little and have found that old plastic almost always becomes brittle. The only difference seems to be to what degree. I looked it uponce and it's apparently from the platicisers outgassing, or something along those lines. Always handle with care.
Click to expand...

Somewhat related, some of the glue (for fabric, I think) used in vintage speakers turns to dust that probably shouldn't be inhaled. I learned that while working on a pair of DCM TimeWindows. Of course, the gorilla snot slathered all over the drivers adhering them to the enclosure was still harder than titanium plated chromium.

Also, the fiberglass batting they used in the cabinets was great for my hands, eyes, and lungs.
 
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Jul 12, 2018 at 11:48 PM Post #15 of 15
I once had an Audio Research D-40 tube amp. Right after I had set the bias (it was sitting on my kitchen table, no speakers hooked up), I noticed that one of the rack handles was loose,
so I decided to tighten it. Keep in mind that this was before I fully understood the kind of voltages that tube equipment operate at. The loose rack handle bolt was just behind the fuse.
While tightening the bolt, I let the hex wrench touch the back of the fuse pin. This was with the amp unplugged, but the power cap's were still charged. I got a boom that sounded like
someone fired a .38 special in the house, and a fireball the size of a softball. After checking the schematic, I discovered that I had grounded 450 volts. The part of the wrench that
touched the fuse holder had a small dimple in it.

Good thing it was the wrench and not my finger. I guess Forest Gump's momma was right.
 
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