in my day job as an electrician I had a huge selenium stack rectifier blow up right next to me. This was as we were powering up a 3300 volt, 1600amp board that had exploded earlier that day (it was a part of the closing circuit for the 3.3kV breaker) so I was already a little jumpy.
I also had a LOT of fun trying to find a new selenium stack rectifier at 2am, let me tell you. I winder how many other 20yo's would know what one acually IS
but forget the fire extinguisher, we had three fire trucks and two dozen firemen at the plant in 6 minutes flat
Minimizing Smoke
My dad taught me an old trick years ago. Install 40W or 60W, 120V incandescent lightbulbs in series with the V+ and V- supplies. At normal idle currents the bulb will glow dimly. If there is a short the bulb will glow considerably brighter. Being nonlinear, the bulb will limit the maximum short circuit current to a reasonable value (< 1A for most rail supplies) while acting as a low resistance at normal amplifier idle currents. Once you are sure the circuit is operating correctly remove the bulbs.
My dad taught me an old trick years ago. Install 40W or 60W, 120V incandescent lightbulbs in series with the V+ and V- supplies. At normal idle currents the bulb will glow dimly. If there is a short the bulb will glow considerably brighter. Being nonlinear, the bulb will limit the maximum short circuit current to a reasonable value (< 1A for most rail supplies) while acting as a low resistance at normal amplifier idle currents. Once you are sure the circuit is operating correctly remove the bulbs.
I had a nice fat DC power supply at TAFE & I remembered hearing a nice trick about making a cheap arc welder with two lead pencils.
So once pencil as + and the other as -, touch the two ends and you can draw out a nice big arc, this all proved true as did the huge temperature generated that the pencil designers had failed to take into consideration when coating the carbon centre of the pencil with wood! I mean what were the 2b designers thinking.
A nice fire in the middle of the bench concluded the experiment.
So once pencil as + and the other as -, touch the two ends and you can draw out a nice big arc, this all proved true as did the huge temperature generated that the pencil designers had failed to take into consideration when coating the carbon centre of the pencil with wood! I mean what were the 2b designers thinking.
A nice fire in the middle of the bench concluded the experiment.
Perfect!!
Hi analog_guy,
You get a whole bunch of "attaboys" for mentioning this tip. I'm going to be trying this the next opportunity I get. Thank you!
-Chris
Hi analog_guy,
That's actually a great idea! I hadn't even thought about this, but of course the idea is perfect! Once you stop to think about how the resistance of a lamp varies, it makes so much sense that you feel stupid for not thinking of this on your own. I don't know about you, but I feel really stupid right about now.
You get a whole bunch of "attaboys" for mentioning this tip. I'm going to be trying this the next opportunity I get. Thank you!
-Chris
Hi _-_-_Adam,
I used to operate carbon arc follow spots. You haven't lived until you've seen these in action. They are pretty loud too. You can feel the heat when one of these hit you on stage over 100 feet away. For a real thrill, try to strike the arc from off. It's violent.
Know how to tell a follow spot operator? Look for the sunburn in vertical stripes on the guy's cheek. These will give you a tan if you aren't careful. The guy may be deaf as well. I don't think they are used much any more.
-Chris
I used to operate carbon arc follow spots. You haven't lived until you've seen these in action. They are pretty loud too. You can feel the heat when one of these hit you on stage over 100 feet away. For a real thrill, try to strike the arc from off. It's violent.
Know how to tell a follow spot operator? Look for the sunburn in vertical stripes on the guy's cheek. These will give you a tan if you aren't careful. The guy may be deaf as well. I don't think they are used much any more.
-Chris
I always tested my amps from a lab supply initially. Since it uses LM317/337s it has very limited output current so can't cause such damage quickly.
If this is unavailable, use your full power supply (once it has been tested with a light bulb in series) but with 100ohm 10W resistors in each power lead. These should help to limit the damage if something is wrong, but are low enough to let you test DC offset, output oscillation and other functionality before a full power test
If this is unavailable, use your full power supply (once it has been tested with a light bulb in series) but with 100ohm 10W resistors in each power lead. These should help to limit the damage if something is wrong, but are low enough to let you test DC offset, output oscillation and other functionality before a full power test
Yeah, I have been thinking more of us maybe should consider getting a variac
I have found several at prices no higher than possible burned components
Any suggestions about how big we should go fore
Would this one work ? http://www.conrad.de/ce/de/product/516503/REGELTRAFO-ESS-102/2170290
Or is this just a no good isolating vario, and we need an auto vario trafo ?
Hi Lars,
I use a 2 amp auto-former style variac on my bench, it covers most things I need to do. For larger amplifiers and tube amps, you might want to look in the 5 ampere range. Larger amps still need something along the likes of a 10 ~ 15 ampere unit. I have the 2 A bench unit, a 5 A unit that is also isolated, and a 10 A variac as well. I also have isolation / step up / down transformers for 230 VAC stuff.
Since you are in Europe, cut all those current ratings in half. If you have a 5 A unit, you don't really need a 2 A unit.
I also run into situations where I need to power up different parts of a circuit and have control over everything. A Carver PM 2.0 would be an example of that. Anything using a switching power supply needs more than one variac to power up safely. With a switcher, I power up the housekeeping stuff first using a DC power supply. Then I may use another DC supply to apply controlled power to the filtered mains portion. After that, I use a variac to increase the AC mains voltage while running the housekeeping stuff off a DC supply. At some point, the switcher will supply enough energy to run the housekeeping supply, running the DC supply through a diode allows a safe and automatic hand-off between the two operating modes. There are amps out there that have multiple supplies, more than just two. That's where the other small variacs come in.
I guess the short answer is that you need to assess your own type of work to determine what you need. Having a little too much is fine, large overkill is a pain to live with unless you build it into your bench. The 10 A variac I have seldom comes out to play, but it's worth it's weight in gold any time it's needed.
For the difference in money, you may be wise to opt for the "REGELTRAFO ESS 104". That would equate to an 8 A unit in North America. You could then run a 120 V device up to 4 A - so still worthwhile.
I pop fuses in my little one sometimes when I forget it's turned up when I turn the variac unit on. I'm really careful about this, but it still happens. I have a circuit breaker ready for the next time I have to work on it. Fuses cost!
-Chris
I use a 2 amp auto-former style variac on my bench, it covers most things I need to do. For larger amplifiers and tube amps, you might want to look in the 5 ampere range. Larger amps still need something along the likes of a 10 ~ 15 ampere unit. I have the 2 A bench unit, a 5 A unit that is also isolated, and a 10 A variac as well. I also have isolation / step up / down transformers for 230 VAC stuff.
Since you are in Europe, cut all those current ratings in half. If you have a 5 A unit, you don't really need a 2 A unit.
I also run into situations where I need to power up different parts of a circuit and have control over everything. A Carver PM 2.0 would be an example of that. Anything using a switching power supply needs more than one variac to power up safely. With a switcher, I power up the housekeeping stuff first using a DC power supply. Then I may use another DC supply to apply controlled power to the filtered mains portion. After that, I use a variac to increase the AC mains voltage while running the housekeeping stuff off a DC supply. At some point, the switcher will supply enough energy to run the housekeeping supply, running the DC supply through a diode allows a safe and automatic hand-off between the two operating modes. There are amps out there that have multiple supplies, more than just two. That's where the other small variacs come in.
I guess the short answer is that you need to assess your own type of work to determine what you need. Having a little too much is fine, large overkill is a pain to live with unless you build it into your bench. The 10 A variac I have seldom comes out to play, but it's worth it's weight in gold any time it's needed.
For the difference in money, you may be wise to opt for the "REGELTRAFO ESS 104". That would equate to an 8 A unit in North America. You could then run a 120 V device up to 4 A - so still worthwhile.
I pop fuses in my little one sometimes when I forget it's turned up when I turn the variac unit on. I'm really careful about this, but it still happens. I have a circuit breaker ready for the next time I have to work on it. Fuses cost!
-Chris
How about constructing a full functional workshop supply instead 
Seems more convenient to be able to power up a new raw module, BEFORE connecting to final supply or installing into box
And for testing modding experimentals
Shoot ... vario trafo is only with single "primary-secondary" windings....so it would need yet another isolating supply trafo
Seems more convenient to be able to power up a new raw module, BEFORE connecting to final supply or installing into box
And for testing modding experimentals
Shoot ... vario trafo is only with single "primary-secondary" windings....so it would need yet another isolating supply trafo
Attachments
Something like that yes.Shoot ... vario trafo is only with single "primary" windings....so it would need yet another supply trafo
Just regard the Variac as a varible AC voltage source. With the variac on it's lowest setting you can switch on the equipment you need to test & gradually increase the mains voltage. A lot of amplifiers will probably stabilise with 0V DC on their outputs with as little as 20V AC in the UK (10V AC in USA) input. Just don't try to drive any speakers or loads without increasing the AC input voltage further
E2A:-Anything with regulated supplies might be a little more problematic in this respect.
Post #4 here has a setup with a bulb, variac, and isolation transformer. Should we all have one of these setups?
http://www.diyaudio.com/forums/pass-labs/5848-what-kind-variac.html
http://www.diyaudio.com/forums/pass-labs/5848-what-kind-variac.html
my "war" story... In the beginning of my career i blew up three power supplies for a $5M computer (this was in the 80's and this was state of the art computers of the 80's -the mini computer). Each PS cost $100K and was about the size of a modern dishwasher.
after my third experience of flames and smoke i looked very carefully at the PS module and realized that i had been trying to connect a PS made for dual 110v into dual 220v.
the CFO at the company ordered an audit of engineering processes after that, telling everyone that we can't afford 'experiences' like that too often.
i didn't feel like a very big man i tell you that!
however, 20 years later i kept at it. i now have a whole bunch of patents in computer hw and software. i designed some of cpu's that members of this site use daily and i never looked back at my almost career ending experience.
i'd suggest you use this experience as an opportunity to understand what happened rather than as discouragement.
good luck!
after my third experience of flames and smoke i looked very carefully at the PS module and realized that i had been trying to connect a PS made for dual 110v into dual 220v.
the CFO at the company ordered an audit of engineering processes after that, telling everyone that we can't afford 'experiences' like that too often.
i didn't feel like a very big man i tell you that!
however, 20 years later i kept at it. i now have a whole bunch of patents in computer hw and software. i designed some of cpu's that members of this site use daily and i never looked back at my almost career ending experience.
i'd suggest you use this experience as an opportunity to understand what happened rather than as discouragement.
good luck!
Yes i'd love something like that, but i wouldn't like to find the cash for a 13A variac or a 3KW isolation transformer. Buying is bad enough, then you need to install them, the variac would be heavy enough but the transformer would be a two man lift
Talking of explosions & rectifiers... I was testing a 200 cell (2V lead acid cells) 500A battery charger (used to either charge or power the trains that workers used to get in & out of the Channel Tunnel when it was being built) when the rectifier stack went up like a roman candle. I'll never forget that in my life, the heatsinks ended up as slag, there was nothing left of the diodes
Another time i managed to short out a battery bank with a pair of pliers.. The pliers started to vapourize before my eyes. All i saw was this intense white light - you can just about imagine it. Still got the pliers with a rather large amount of steel missing, i kept them as a reminder
Hi jaycee,
As you know, your hobby bench is something you build up over the years, and I've been building mine for over 30 years (maybe even 40 or so ... Hmmmm. yes, I've been at it for over 40 years and still have some original stuff.)
Old hipot testers contain a variac, as do many old industrial panels. Just stay on the lookout. As I mentioned earlier, a 2A model (1 A for you) does most everything I need. The rest is just icing on the cake.
Hi event horizon,
Hi Lars,
Huh? I missed your meaning I think.
Hi DreadPirate,
Nelson's requirements are more srtingent than normal. You will only be using a variac for initial power up or troubleshooting. You will not be running anything up to full power, but Nelson might.
Building a test panel as I have is fun and enjoyable. So it should be for anyone else. You will learn to love some form of AC voltmeter and ammeter. Analog meters are highly recommended for this. The trend is more important than an exact number. You only need to know an approximate value.
-Chris
That's equivalent to an 8 A North American type. Yes, those are expensive here as well. So, do as we all do. Go to auctions, check out flea markets and never pass up a Hamfest. Network with others in your area. It's amazing how much extra stuff people have that can be traded for.
As you know, your hobby bench is something you build up over the years, and I've been building mine for over 30 years (maybe even 40 or so ... Hmmmm. yes, I've been at it for over 40 years and still have some original stuff.)
Old hipot testers contain a variac, as do many old industrial panels. Just stay on the lookout. As I mentioned earlier, a 2A model (1 A for you) does most everything I need. The rest is just icing on the cake.
Hi event horizon,
That's not really reasonable, or if you need something like that, the parts you save would easily cover buying new with new cabinet also. People, think surplus stores and other sales. Even garage sales might reveal some cool stuff.
Hi Lars,
Huh? I missed your meaning I think.
Hi DreadPirate,
Nelson's requirements are more srtingent than normal. You will only be using a variac for initial power up or troubleshooting. You will not be running anything up to full power, but Nelson might.
Building a test panel as I have is fun and enjoyable. So it should be for anyone else. You will learn to love some form of AC voltmeter and ammeter. Analog meters are highly recommended for this. The trend is more important than an exact number. You only need to know an approximate value.
-Chris
Yup, I remember those slip-ups...My first encounter seven years ago - After successfully P to P'ing a Gainclone, I pressed my luck and bought a pricey Zappulse amp (V2.1) modules and had it working first time up. Really impressed myself (kinda hard to really trip up tho). Then I decided to upgrade the caps to bigger caps and re-powered it but accidentally reversed the rails... boy was I mad. It was 2:00am.
My latest fiasco was soldering a loose neutral wire onto an IEC power connector inside an amp, while connected to the mains (again, in a hurry and 2:00 am). I was real careful not to touch the hot lead, but it didn't matter. Nice big spark and smoke. Talked to a couple EE's at work the next day and finally realized what I did. A direct short. My face was literally inches away... won't do that again....
I have finished my basement where my "Electronics Lab" is, and have added three things - a whole house surge protector at junction box (to protect my precious amps from a nasty line spikes and MAYBE a lightning strike in the neighborhood - $50 at Menards), a Ground Fault outlet on first outlet of all circuits, and my "Lab" circuit has an Arc Fault at the junction box. I feel better knowing I have a Ground and Arc Fault protecting me in the event I do something stupid AGAIN.
Oh, I have also bolted up a fire extinguisher too. And finally a Variac!
My latest fiasco was soldering a loose neutral wire onto an IEC power connector inside an amp, while connected to the mains (again, in a hurry and 2:00 am). I was real careful not to touch the hot lead, but it didn't matter. Nice big spark and smoke. Talked to a couple EE's at work the next day and finally realized what I did. A direct short. My face was literally inches away... won't do that again....
I have finished my basement where my "Electronics Lab" is, and have added three things - a whole house surge protector at junction box (to protect my precious amps from a nasty line spikes and MAYBE a lightning strike in the neighborhood - $50 at Menards), a Ground Fault outlet on first outlet of all circuits, and my "Lab" circuit has an Arc Fault at the junction box. I feel better knowing I have a Ground and Arc Fault protecting me in the event I do something stupid AGAIN.
Oh, I have also bolted up a fire extinguisher too. And finally a Variac!
Last edited:
Progress report....
Hi bryantramos79,
I just thought I'd let you know the progress. I have not applied power to it yet.
3 resistors and 2 output transistors definitely gone, but the rest look good. Hey, don't give up on DIY, you did a good job placing the components and your soldering skills are good. Neat job all round.
I feel the problem was using the BD140 with the circuit on the DX website for the Vbias.
I have cleaned the PCB, replaced the dead components and made a new Vbias circuit. I just need to find a power supply. My test PSU found a permanent home in my main system....I must fix that.
Fingers crossed for when I apply power for the first time.
regards
Hi bryantramos79,
I just thought I'd let you know the progress. I have not applied power to it yet.
3 resistors and 2 output transistors definitely gone, but the rest look good. Hey, don't give up on DIY, you did a good job placing the components and your soldering skills are good. Neat job all round.
I feel the problem was using the BD140 with the circuit on the DX website for the Vbias.
I have cleaned the PCB, replaced the dead components and made a new Vbias circuit. I just need to find a power supply. My test PSU found a permanent home in my main system....I must fix that.
Fingers crossed for when I apply power for the first time.
regards
Attachments
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.