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Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

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Old 8th December 2011, 07:40 PM   #1
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Join Date: Jan 2007
Default In a Pinch

On a whim, I picked up a couple of 3V AC adapters that Radio Shack was clearancing for $2 each this afternoon. My initial thought was that I could lose the rectification stages and just wire the two transformers back-to-back for line isolation purposes.

Once I started cracking the cases, however, it occurred to me that their low voltage rating and small size pretty obviously dictated that they must be switching supplies. While this scuttled my original plan, I was pleased to find that each unit contained a couple of miniature 4.7uF electrolytics rated at 400V, as well as a quartet of 1n4007s and a metal film cap rated at 1kV.

While all of this stuff can be routinely sourced online, sometimes it's handy to have a quick source for oddball parts. This is particularly true of the high voltage caps that RS doesn't stock individually.

Along these lines, does anyone have any tips for scrounging everyday items for parts in a pinch?

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Old 9th December 2011, 12:13 AM   #2
Enzo is offline Enzo  United States
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Oh my.

Dumpster diving.

I started learning electronics in the 1950s, and a regular place to visit for me was the alley behind a couple local TV repair shops. I'd find old dead TVs they were throwing out. I'd either haul them home, or take the chassis from them. Then I got home and disassembled them saving as many resistors and caps and controls and tubes and transformers and god knows what-all. Mom throws out a dead alarm clock? Well at least there is one free power cord on it I can save. And SCREWS! EVerything is held together by screws, and stripping stuff down leaves a lot of screws for you.

And in that era, not long after World War 2, there were a lot of surplus military electronics stores. We had several in our area. SO I could go in them and buy old radar consoles, or radios, or other communication gear. SOme sold equipment by the pound, others tried to price things individually. Plus ther were the military spare parts. A 5k pot for something came sealed in a foil pouch wrapped in plastic, with a dessicant pack thrown in, then packing material all stuffed into a cardboard box with a descriptive label. Now 50-60 years later, I still have one of those pots unopened. I have plenty of pots in my drawer, and this one is more for show and tell than parts stock. But I got my start using those old resistors and things from TV sets.

Fast forward to today. I still find it cathartic to strip something down. Now and then I feel unproductive, so just for a diversion I get an old VCR and strip it. The older the better. From it I get a power cord, a massive collection of metric screws, a little power supply board with power transformer. I can use the transformer to make something, or even use the whole little board if its regulated voltages are useful. Most of the ICs are specific to the VCR, but if I had zero cash, I suppose I could suck out a couple adio op amps from the audio area. Lots of little C-clips too. The heads and other low signal level circuits will usually have some small shielded cable. That can be useful for shielding a small run of something. Like from an input jack back to a tube grid.

Dead VCRs are not hard to find. And still today there are electronics repair shops, and I bet there are trash bins behind them. CAssette decks are similar though maybe less bountiful. SOme screws, a power cord, a power transformer, small shileded wires.

I run a commercial shop, so I don't sell used or salvaged parts as a rule. But every now and then... One time I needed a small signal transistor. I forget the package, but smaller than a TO92. I just didn;'t have anything like it in my drawer. I then remembered I had stripped out a cassette deck the night before and the board was still in my trash. Sure enough, I found a small signal transistor on that board that worked like a charm. SO if you are a kid dabbling in small effect pedals or something, and have no money, I bet you could find a wad of little useful transistors in a cassette deck.

And a lot of that stuff has a headpones jack, usually on a little board. Might be useful.

CD players and DVD players have all gotten so specific any more that I find little else but a power cord on them. SOme don't even have screws, they snap together.

I have a few little TVs sitting around. Since the conversion to digital TV, they will remain forever useless now. They are on my strip-me-down list for when I find myself bored in the future. Same sort of parts bounty. Unlike audio circuits, some TV circuits do use higher voltage caps. On the other hand, as someone who has serviced many video monitors from the arcade industry, worn out caps is THE most likey failure in one. So don;t assume salvaged parts are good without testing them.

But anything that makes audio - cassette, VCR, CD player - will have some RCA connectors and probably a few op amps. Things like TVs that have speakers will also have small power amps to drive the speakers, maybe discrete, maybe an IC. And not to mention the small speaker itself as maybe useful.

Things like CD players also often have a boatload of small tactile switched behind the buttons - tiny push buttons.

One man's trash is another man's treasure, after all.
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Old 9th December 2011, 03:15 AM   #3
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Location: Jeffersonville, Indiana USA
I blew up an amp driver pcb including about 20 diodes and a few rice grain caps. No problem- I had a wyse terminal PCB fished out of the trash with all that stuff. Most of the resistors & capacitors went into the junk bags too. My collection of resistors & capacitors started with R***** S***** grab bags in the 1960's, but resistors disk and film caps from old TV's, terminals, went in there. I have stuff sorted by decade so I don't have to paw through too big a pile. The transistors are usually too high voltage to fool with, but I pile them up just in case. Electrollytic caps I dont' save, they are usually worn out or the rubber is age cracked.
PCAT power supplies are full of useful things like scrap wire in 5 colors, diodes, small resistors & caps, opto-isolators, turn on surge thermistors, lightning supression MOV's, fuse holder clips. They blow up about once a year, I have a stack of 4 or 5 dead ones. I've rewound a couple of PCAT toroids to make 25 turn chokes to prevent RF hash getting into preamps etc. Maybe some day I'll get energetic and try to redesign one of these PCAT supplies to make some useful voltage besides +5 @ 20 A, etc. Usually an E-cap and a few Fet's is what is blown up. The opto-isolators are slated to make an amp safety circuit, to use detected ouput DC to turn on a triac grounded to the input power circuits, to pull a 120 VAC coil relay and break the speaker circuits instead of shorting the output and burning the PCB lands as OEM.
Old PC's at the charity resale shop are useful for $3 also. Besides dead power supplies, they have LeD,s switches, fans, and the cases I have cut up to make brackets for 8 ohm 450 watt resistors, fan shrouds for my amp, and other useful things.
Old organs are full of limited bandwidth power amps, speakers, switches, fans, solenoids, relays, inductors, RLC parts, fuse holders, etc etc. People are glad to get them moved out of the house. Some of them are worth restoring, but I have a friend that has a storage shed full of free Wurlitzers. One is wonderful, but the second, third, fourth, beg to be turned into something else. I'm looking at a Hybrid organ with Hammond tone generators for pitch stability, op amp triangle waves Hammond didn't have until the 500 lb 360 E-cap X66, and Wurlitzer tone filters. W stabilized their pitch oscillators with a 50W electric heater- so primitive (and ineffective).
Isn't retirement wonderful! So much trash, so little time.
Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300

Last edited by indianajo; 9th December 2011 at 03:28 AM.
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Old 9th December 2011, 06:50 AM   #4
Enzo is offline Enzo  United States
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We all start somewhere. It is easy for an old boy to look down his nose at some youngster, but I've been there. Had plenty of time and no money. Old used parts were better than nothing, and good enough for learning. And once in a while they can even bail out a pro from a sticky situation.
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Old 9th December 2011, 07:04 AM   #5
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Location: San Antonio
I have done/still do a lot of this sort of thing. In fact I just mentioned in another post... I cut the chip amp audio circuit from a dead projection TV main board. It only needs input caps and a power supply. And some cleaning. Below is a webcam shot. So sometimes it's possible to scrounge an entire subassembly. I've found some big screen TVs with 5532-based audio circuits. If you run across a broken Peltier electric cooler grab it and extract the heatsink. They're always sizable aluminum jobs that'd probably cost you $20 or more store-bought. LEDs, LM358s, LM339s, diodes are all fairly ubiquitous. TVs are probably a best bet for HV parts. But unsurprisingly, true oddball parts aren't easily found in everyday items.
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Old 9th December 2011, 08:56 AM   #6
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Location: Rotherham, England
And don't be afraid to pop around to your local pro audio or AV company to see if they have any junk that's not economical to repair. Many's the company I've visited that has something like a pile of old Crown Powerbase amps holding up a workbench or propping a door open. If you explain yourself, most will be quite happy to donate stuff to the cause.
Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
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Old 9th December 2011, 02:05 PM   #7
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Great posts! Sofaspud reminded me of a recent conversation with a coworker. His rear-projection TV finally gave up the ghost and he upgraded to an LCD, but he was considerate enough to ask if I had any interest in scavenging the old set for parts. It was hard to turn down the adventure, but space in the apartment is at a bit of a premium with a newborn. 8]
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Old 10th December 2011, 12:59 AM   #8
Enzo is offline Enzo  United States
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There is a thought. Pro audio/ guitar amp shops. I run one. Sitting next to me is a dead Bogen solid state amp. power amp section is blown, and I won;t ever repair it. But good power transformer and other useful stuff in it, not to mention sturdy metl housing for some project. If some interested novice came to my door, I;d give it to him. Or her. I think most of us have a pile of dead things hanging around "you never know when it might come in useful." Probably could be talked out of some of it.

I have some regular visitors, guys trying to learn about audio electronics on their own. I offer advice and the occasional part. Interesting to watch their progress over time. They start out not knowing which end of a battery does what, and progress through voltage and resistance, and eventually we are talking about biasing a transistor. I can;t be the only tech around willing to talk to hobbyists and help them out.
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