HEY DONT THROW AWAY THOSE BROKEN PC's PSU TOO!

[bassmannate]

I don't know. All I know is that we hire a shipping company called Transgroup to come and pick it all up. We load it into HUGE boxes on pallets and send it off. It's really a huge pain for those of us in the warehouse.

[JKowalski]

I'm well aware you are entitled to your personal opinion, I just thought considering it, you have nothing valuable to add to a discussion about salvage from old electronics.  And I'm sure your sound through a Tubescreamer into a Twin sounds exactly like you playing through a Clari(not) and Aqua Puss into a JCM 800.  Not sure why you're even a member here, really.   

What's with this infantile hostility?  Jeebers...nice to know we've got thread gestapo roaming around to keep everybody's thoughts and comments in line, huh?  Grow up, change your diaper, and stop trying to make enemies, clown. 

I don't know if you realize it, but your response was the worst one possible. You condemn him for childish insults, while making your own as well.

If you don't like what someone has said, please either do not respond or respond in an at least neutral and constructive way.

I love this forum for it's comparative civility to others on the web. I'd like to keep it that way, and I think everyone can agree with that 

[SpencerPedals]

I'm well aware you are entitled to your personal opinion, I just thought considering it, you have nothing valuable to add to a discussion about salvage from old electronics.  And I'm sure your sound through a Tubescreamer into a Twin sounds exactly like you playing through a Clari(not) and Aqua Puss into a JCM 800.  Not sure why you're even a member here, really.   

What's with this infantile hostility?  Jeebers...nice to know we've got thread gestapo roaming around to keep everybody's thoughts and comments in line, huh?  Grow up, change your diaper, and stop trying to make enemies, clown. 

I'm guessing you agree it was a valid point, hence the name-calling and, ironically, accusations of me doing the name calling.  I made a real point and you want to hurl insults, so I invite you to please do it via PM so people here can go about the talk of what they're finding.  Bickering in private is much more polite to the other folks who have understandably voiced their distaste for it.

Speaking of salvage, I've been running into a lot of transformers in old, random thing that would not have schematics floating around for them.  Having only built guitars, one amp, and stompboxes, I'm not too familiar with exactly how to identify them.  How does one go about finding specs on a transformer that is ill-marked and of unknown origin?  Or I'd also be interested in a good amp-related transformer reference, if someone has one.  The few searches I did didn't answer any of the kinds of questions I had.  This should probably be asked in an amp-building forum, but essentially what I'm getting at is: when I take things apart with these audio transformers, how can I go about figuring out what they would be well-suited for.  The organ I am parting out has a very large transformer on its amp and I don't want to use the amp itself and just hook it up in a cab; I'd like to use it for an amp of my choosing instead.  It was a tube organ and had a lot of grouped tube modules, with 5 or 6 tubes in each, with multiple small (strange looking) transformers along side them, and I was also wondering if those could be tested for usefulness.  I can upload a pic of that last part, if we have a guru in the house for that.

[JKowalski]

Speaking of salvage, I've been running into a lot of transformers in old, random thing that would not have schematics floating around for them.  Having only built guitars, one amp, and stompboxes, I'm not too familiar with exactly how to identify them.  How does one go about finding specs on a transformer that is ill-marked and of unknown origin?  Or I'd also be interested in a good amp-related transformer reference, if someone has one.  The few searches I did didn't answer any of the kinds of questions I had.  This should probably be asked in an amp-building forum, but essentially what I'm getting at is: when I take things apart with these audio transformers, how can I go about figuring out what they would be well-suited for.  The organ I am parting out has a very large transformer on its amp and I don't want to use the amp itself and just hook it up in a cab; I'd like to use it for an amp of my choosing instead.  It was a tube organ and had a lot of grouped tube modules, with 5 or 6 tubes in each, with multiple small (strange looking) transformers along side them, and I was also wondering if those could be tested for usefulness.  I can upload a pic of that last part, if we have a guru in the house for that.

For power transformers, just stick 120VAC on the primary and write down all the secondary voltages. Then, measure the size of the transformer, and compare it to various ones on mouser or somewhere - when you find one that is approximately the same size, look at it's VA rating and typically that will be a good approximation of the VA rating of yours. Those two things are all you really need to know most of the time.

For output transformers, hook up a function generator to the primaries and send it some easy value AC like 500Hz 10V P-P. Measure the AC voltage which appears on the secondary. Then, divide the input AC by the output AC. Finally, square the answer. This number represents the impedance ratio (it's a ratio cause its YOUR NUMBER / ONE ). Using this impedance ratio, you can figure out what the impedance of the primary winding is with a given load by multiplying the impedance ratio by the load (I.E. impedance ratio x 8ohms). You should get a value that is between 5K to 25K or so -  i think that's the standard range....) Finally, this number can be used to figure out what kind of power tubes the transformer is useful for. Tube data sheets have a standard value for this impedance. You can also approximate the VA rating in the same way as the PT, just look at output transformers on the web and compare dimensions until you find a match.

Typically, transformers are made in certain standard VA ratings, and so many of them conform to a standard size.

[aussie-guitars]

I've found many great parts by ratting old TV's and Stereo's people throw out, you would be surprised at what some people throw away.

[earthtonesaudio]

For power transformers, just stick 120VAC on the primary and write down all the secondary voltages.

For an unknown transformer, it's an EXTREMELY GOOD IDEA to use a very low voltage for testing the windings.  Like 2VAC or less.  The reason is that (especially if primary/secondary are not marked) you have no way of knowing what voltages will come out the other end, or if they might be lethal.

[JKowalski]

For power transformers, just stick 120VAC on the primary and write down all the secondary voltages.

For an unknown transformer, it's an EXTREMELY GOOD IDEA to use a very low voltage for testing the windings.  Like 2VAC or less.  The reason is that (especially if primary/secondary are not marked) you have no way of knowing what voltages will come out the other end, or if they might be lethal.

That's true. You don't want to stick 120VAC on the heater windings and have 10 kilo volts coming out the other windings!

If you really have no idea where to start, look at the DC resistance of the windings. For high voltage tube transformers, the high voltage windings will typically have a higher resistance then the primaries, and the primaries will have a higher resistance then the heaters. For example, on my 500VAC C.T. PT i have lying around, the resistances were

secondary: 312 ohms
primary: 12 ohms
heaters: 0.8 ohms

If you are taking this out of something, it really saves you a lot of trouble to write down where all the windings go before you remove it and sticky it to the transformer!

[Processaurus]

For desoldering parts, anyone use a blow torch or heat gun on the solder side to melt the solder, then wack the board on something to knock the parts out? That's the fast way, probably want to cover your eyes and face, wear gloves, and not breathe to deep...

[arizonabay]

I have a pc PSU which was sitting under my bad for more than a year.

I heard somewhere that caps can store so much current that they could kill you.

Can i harm myself while i took apart that PSU?

Can I bump this post as I am interested in any dangers that might be lurking in pc psu's

Thanks
Matt

[earthtonesaudio]

Most PCs don't require high voltages so the filter caps on the output side probably aren't lethal.  (But could still probably give you a strong "bite," and cause you to seriously cut your hands on the razor-sharp edges of the case when you instinctively jerk away!  One of the most common electronics-related injuries is getting cut.)

The input side, however, almost always contains one or more high-voltage, high capacity caps for filtering the mains supply voltage.  These should be treated as very dangerous.  There might be more dangers I don't know about, so find out as much as you can about the specific device you have before you go exploring. 

This should go without saying, but advice from an internet forum is not sufficient to protect you from the many dangers you might encounter in electronics gear.

[JKowalski]

One of the most common electronics-related injuries is getting cut.

I always burn myself with the soldering iron.

Or jab super sharp parts leads halfway through my fingers or up my fingernail.

[Cliff Schecht]

I have a pc PSU which was sitting under my bad for more than a year.

I heard somewhere that caps can store so much current that they could kill you.

Can i harm myself while i took apart that PSU?

Can I bump this post as I am interested in any dangers that might be lurking in pc psu's

Thanks
Matt

The residual charges that can hurt you are stored in the huge caps in the power supply. If you were to plug in the power supply for a bit, unplug it quickly and touch the caps then yeah, you're going to get shocked pretty badly. As it turns out though, just about every switching power supply has some sort of internal minimum load to ensure stability of the power supply. This minimal load will slowly drain charge out of the caps over time and means that if the power supply has been sitting for a while, all of the energy will be drained from those caps. It never hurts to short the capacitor leads together to ensure that no charge is present though, otherwise you may be in for a nasty surprise!

[doitle]

One of the most common electronics-related injuries is getting cut.

I always burn myself with the soldering iron.

Or jab super sharp parts leads halfway through my fingers or up my fingernail.

I definitely agree with cuts being the most common... I remember when I was repairing a friend's DVD Drive / Taking it apart and cleaning out a disc that shattered in there... When I was done I looked at my hands... it looked like I had been climbing barbed wire fences or something. I was COVERED in cuts.  I've got a strange... problem though that a lot of injuries like that I can't feel...

I also accidentally kicked the cord on my pencil soldering iron but caught it... You know, reflexes to catch something falling... Except it was all the way heated up. Anyhow I caught it on the top of my hand like balancing with the whole length of the tip touching me and I was like "phew"... and heard the hair on the back of my hand burning and went "Oh shi-!" and grabbed it by the handle... I had a big blistered soldering iron shaped burn on the whole back of my hand but I couldn't feel it... I don't know if it's an asset or a liability...

[jacobyjd]

One of the most common electronics-related injuries is getting cut.

I always burn myself with the soldering iron.

Or jab super sharp parts leads halfway through my fingers or up my fingernail.

That can be a dangerous thing if you're working with electronics.

Nice if you're a hockey goalie, though :-P
I definitely agree with cuts being the most common... I remember when I was repairing a friend's DVD Drive / Taking it apart and cleaning out a disc that shattered in there... When I was done I looked at my hands... it looked like I had been climbing barbed wire fences or something. I was COVERED in cuts.  I've got a strange... problem though that a lot of injuries like that I can't feel...

I also accidentally kicked the cord on my pencil soldering iron but caught it... You know, reflexes to catch something falling... Except it was all the way heated up. Anyhow I caught it on the top of my hand like balancing with the whole length of the tip touching me and I was like "phew"... and heard the hair on the back of my hand burning and went "Oh shi-!" and grabbed it by the handle... I had a big blistered soldering iron shaped burn on the whole back of my hand but I couldn't feel it... I don't know if it's an asset or a liability...

[SpencerPedals]

For power transformers, just stick 120VAC on the primary and write down all the secondary voltages.

For an unknown transformer, it's an EXTREMELY GOOD IDEA to use a very low voltage for testing the windings.  Like 2VAC or less.  The reason is that (especially if primary/secondary are not marked) you have no way of knowing what voltages will come out the other end, or if they might be lethal.

Do you use some sort of bench power supply to send smaller voltages as suggested?  Or have recommendations of one?  My current arsenal is set up for stompboxes, so I have yet to move on to larger equipment and apologize for my lack of knowledge there.

[earthtonesaudio]

I don't have any specialized equipment for this, but you'd be quite safe using an audio frequency oscillator circuit as your test oscillator.  Something like the GEOFEX "quick and dirty test oscillator" tweaked to output 60Hz would probably be fine.

[Cliff Schecht]

For power transformers, just stick 120VAC on the primary and write down all the secondary voltages.

For an unknown transformer, it's an EXTREMELY GOOD IDEA to use a very low voltage for testing the windings.  Like 2VAC or less.  The reason is that (especially if primary/secondary are not marked) you have no way of knowing what voltages will come out the other end, or if they might be lethal.

Do you use some sort of bench power supply to send smaller voltages as suggested?  Or have recommendations of one?  My current arsenal is set up for stompboxes, so I have yet to move on to larger equipment and apologize for my lack of knowledge there.

I usually do what Alex said with a function generator unless I miraculously have an autotransformer near by. Those are big and expensive though so I usually avoid them if I can.