Resistors and stuff

[Peter Venkman]

So I can across some old power supplies, telephones, VCRs, and mother boards for old computers. I've been harvesting the caps, resistors and diodes out of them just to get some mobility in my hands and help out my eyes when it comes to solderinng such small components. I've found glass diodes, ceramic, film, and germanium diodes, and a metric ass ton of resistors. I down loaded and app to help identify the resistors based on the color codes and they all seem fairly useful, however most of them at 1/2 instead of 1/4. I know that 1/4 is pretty much the go to size for resistors on these tagboard builds but what would happen if inswappednout some of the 1/4s for the 1/2s. I have a ton of different varieties and instead of being blue with 5 color bands, they are tan with only 4 color bands. I know that I'll be able to use almost all the capacitors and diodes I've found but I'm just wondering should I even bother pulling out the tan resistors. I've pulled out an LOT of blue ones but not nearly as many that were tan

Also anyone know of an app for identifying capacitors. The resistor app i downloaded is great for my dyslexia.

[rocket88]

Honestly nothing different will happen, as they can handle the power of a pedal without any issues. They'll just take up more space on the board and may not lay flat like on the layout. The tan resistors are probably carbon film, which there's nothing wrong with. They usually have a slightly lower tolerance, either 10% or 5%, so if you have resistor makes 10k it really could be 10k + 10% or 10k - 10%.

Not sure about an app to identify caps. But, I do not a few sites that tell you how to read the markings.

[PEPPER!]

Recycling stuff is good and it's great practice for de-soldering and learning to recognize components.  I've built whole pedals with recycled parts.  Some caps are labeled with the modern international code (104=100n/.1uF, etc) and some are not. I recently got hold of a huge bag of old 60s & 70s components from a retired TV repairman and I sorted the non-obvious stuff by looks, then by whatever code I could find on them, then finally measured them with a multimeter to sort them.  It can hard to determine the voltage rating of a mystery capacitor, but if it's not electrolytic it's likely to be high enough to use in stomp pedal without a problem.  If is electrolytic and and it's old (like 80s or earlier) maybe test a couple to see how close to the printed capacitance you really are.

I have an older iPhone & know they have a couple of free/cheap electronics buddy type apps for identifying resistors & caps.  I just printed out a couple of the capacitor code charts & remember them well enough now that I rarely look.

Pulling the resistors is up to you.  I'll only pull old carbon comp (brown) resistors if they are the nice old Bradley-Allen ones because they look cool and I can sometimes use the spares for old tube amps.  I'll also pull 2W and 5W resistors  - the big blocky ceramic guys - and leave the rest alone as new ones are so cheap.  That said, you're fine using a 1/2W resistor instead of a 1/4 in a stomp pedal.

More good parts to harvest - knobs, trimmers, potentiometers, LEDs, small transformers, op-amps, power and regular transformers, covers for large transformers, little tin shielding boxes, and wire.  

[Frank_NH]

I've recycled parts from my OWN builds that, for various reasons, didn't turn out as I'd liked.  I generally harvest the caps, sockets, ICs, transistors, and diodes - but only if the leads are long enough and they are undamaged. Resistors I tend not to harvest, but if the leads are long enough, I may pull some selected values.  Toss the rest in the trash.

[Silver Blues]

Yeah salvaging stuff is great fun. I have built lots of things with salvaged parts. I have a large collection of old broken boards to pull from, even one with an almost complete-range selection of 1/8W metal film resistors that I pull from if I need a part to span 3 rows. I think your resistors question has been answered already, but as far as apps go, if you have an Android device, my go-to app is ElectroDroid. Basically everything you'd ever need in there with a nice GUI.

[induction]

I agree with all the above advice except for this bit:

PEPPER! wrote

If is electrolytic and and it's old (like 80s or earlier) maybe test a couple to see how close to the printed capacitance you really are.

Any old electrolytics you find you should just throw away. All electrolytics go bad after a while, no exceptions. They go bad faster if they aren't held under a polarizing voltage (ie. in circuits that haven't been used in a while, or even untouched, still-in-the-box NOS). When they go bad, they usually go short circuit (ie. they turn into a jumper). This often results in a circuit that simply stops working (and good luck figuring out why), but if you use them as power filters, they can short the positive and negative voltage rails (which can kill your power supply), and may even explode (which can kill other components on your board, and smells awful). Frustratingly, sometimes they will still test within tolerance on a cap meter.

In one lab I worked in, we had several turbopumps for maintaining vacuum inside our particle accelerator. Each turbopump had its own controller. One year, all the controllers started failing, one after another - they just refused to turn on, which meant the accelerator was out of operation until they could be repaired. The company that made the controllers gave us an estimate of about $2k per controller plus shipping just to look at them (actual repairs were extra), and a turnaround time of about a month per controller. The first time it happened, I bought a bunch of electros from Radio Shack on a hunch, and just replaced every electro in the controller. Problem solved for less than $3 with only a few hours of downtime.

[Frank_NH]

"In one lab I worked in, we had several turbopumps for maintaining vacuum inside our particle accelerator. Each turbopump had its own controller. One year, all the controllers started failing, one after another - they just refused to turn on, which meant the accelerator was out of operation until they could be repaired. The company that made the controllers gave us an estimate of about $2k per controller plus shipping just to look at them (actual repairs were extra), and a turnaround time of about a month per controller. The first time it happened, I bought a bunch of electros from Radio Shack on a hunch, and just replaced every electro in the controller. Problem solved for less than $3 with only a few hours of downtime. "

That's a great story, induction!  Radio Shack saves the day!

I too don't care too much about old caps in general.  I ** do ** care about caps being at least close to the value written on the part.

Question - if a cap goes bad (shorts out) does that only reveal itself if there is electricity flowing through the cap?  That is, with the voltage off, a cap will still be an open circuit, correct?  That would be helpful to know when I debug circuits, looking for bad components.

[induction]

Frank_NH wrote

Question - if a cap goes bad (shorts out) does that only reveal itself if there is electricity flowing through the cap?  That is, with the voltage off, a cap will still be an open circuit, correct?  That would be helpful to know when I debug circuits, looking for bad components.

In my experience, when a cap goes bad, all bets are off. It may read as a short circuit on the resistance setting of your DMM, and still read within tolerance on the capacitance setting. Or it might not. Sometimes they work fine for a while, and then intermittently crap out. They make troubleshooting a real nightmare. The way I deal with it is 1. Don't use old electros in new builds, and 2. If you find an old electro in a circuit that's acting up, replace it. Maybe that fixes it, maybe not. If not, well, at least you won't have to replace that cap in the near future.

According to RG, the shelf life of good quality electros that never get used is about 5-10 years. Using them regularly (subjecting them to polarizing voltage) extends their life because the voltage can help them self-repair. But if the circuit is such that the cap gets hot when it's turned on, then the lifespan diminishes because heat aids in their degradation.