Through-hole 1% non-magnetic metal film resistors are getting hard to come by. And spending a buck a pop for them gets old quick, not really knowing if they're non-magnetic types until you receive them.
Some of you no doubt already know this, but quite a few excellent through-hole passive parts (especially 1% metal-film NM resistors) can be salvaged from 70's- and 80's-era test equipment. Many of these pieces have little or no market value any more and can be picked up for scrap value. It makes a lot of sense for a hobbyist to keep a few pcb's from them in the garage as a source of parts for ongoing projects. Of the major brands, here's a brief list of ones to keep an eye out for.
HP: Anything HP with analog circuitry and made in the USA from say late-70's to late-080's is chock-full of Dale CMF55 non-magentic resistors, with a sprinkling of RN60 to RN70s when needed. Typically hundreds of them per unit. After that they moved more to Roderstein (which are magnetic) and then to surface mount. Units made in Germany use mostly Rodersteins.
Most of HP's axial film caps were made by TRW, which tend to be very good. Most radials are Wima.
Wavetek: Wavetek function generators used TRW RN55's exclusively, all of them non-magnetic and excellent.
Tektronix: Old Tek stuff is more hit and miss. They used a variety of vendors for metal films, some magnetic, some not. I don't tend to save Tek pcb's for parts.
Interstate Electronics: A bit of a sleeper. These guys used very high-quality parts throughout. I just scrapped one of their P25 pulse generators; it has 140-150 Dale RN60 NM's on the main pcb. Nice heatsinks too.
Generally, any piece of gear for which DOD or DOE was the primary customer probably has high-quality passive parts inside.
Ones to avoid:
Systron Donner. Not worth the trouble, IMO.
Fluke. Their precision resistors were nice, but their general-purpose parts were nothing special.
Feel free to add to the list.
Some of you no doubt already know this, but quite a few excellent through-hole passive parts (especially 1% metal-film NM resistors) can be salvaged from 70's- and 80's-era test equipment. Many of these pieces have little or no market value any more and can be picked up for scrap value. It makes a lot of sense for a hobbyist to keep a few pcb's from them in the garage as a source of parts for ongoing projects. Of the major brands, here's a brief list of ones to keep an eye out for.
HP: Anything HP with analog circuitry and made in the USA from say late-70's to late-080's is chock-full of Dale CMF55 non-magentic resistors, with a sprinkling of RN60 to RN70s when needed. Typically hundreds of them per unit. After that they moved more to Roderstein (which are magnetic) and then to surface mount. Units made in Germany use mostly Rodersteins.
Most of HP's axial film caps were made by TRW, which tend to be very good. Most radials are Wima.
Wavetek: Wavetek function generators used TRW RN55's exclusively, all of them non-magnetic and excellent.
Tektronix: Old Tek stuff is more hit and miss. They used a variety of vendors for metal films, some magnetic, some not. I don't tend to save Tek pcb's for parts.
Interstate Electronics: A bit of a sleeper. These guys used very high-quality parts throughout. I just scrapped one of their P25 pulse generators; it has 140-150 Dale RN60 NM's on the main pcb. Nice heatsinks too.
Generally, any piece of gear for which DOD or DOE was the primary customer probably has high-quality passive parts inside.
Ones to avoid:
Systron Donner. Not worth the trouble, IMO.
Fluke. Their precision resistors were nice, but their general-purpose parts were nothing special.
Feel free to add to the list.
Why are you worried about magnetism? Normally this only shows up at high currents and low-impedances where the tiny inductive reactances can start to have an effect on signal quality (such as loudspeaker output relays and terminals/connectors). For low level signal processing this is normally well below the noise floor.
Try this experiment. Build one channel with non-mags and one without. See which one sounds better to you.
Conversely, why buy new when you have perfectly good, if not superior, used ones sitting around?
(Reduce, reuse, recycle...)
No, the correct test is using an AP analyzer and do some proper measurements. The distortion levels are absolutely below human perception by orders of magnitude when you start comparing different metal film resistors!
Wish I had one!
Why is that 'the correct test'? In my book, the fact that a particular test does not reveal a difference that you can clearly hear just means the test is inappropriate.
BTW, I don't have an AP, either, and don't lust for one.
It is a bit odd to diss my suggestion of listening to one of each, and then claim that the measured distortion levels are "below human perception"...
I will confess, it is only this year that my opinion on this matter has changed. What made the difference is working on headphone amplifiers. Much easier to hear such differences.
Having said all that, my purpose in posting this was not to argue this point, it was just to bring to people's attention this great source of high-quality parts, some of which are heading towards unobtanium. Tons of such equipment finds its way to recycling centers and landfills every day. It makes total sense for a hobbyist to reuse such parts.
I usually scavenge as much as I can before I throw out electronics but can’t say I unsolder and save resistors. For one I usually use 1% precision, two my pcbs have standard lead spaces that probably won’t match resistors that are pulled, it’s a lot of work removing sorting. But I give you credit for wanting to re-use.
Same here until recently. I've taken hundreds of pounds of pcb's to the recycler and never thought about scavenging the small resistors. From now on they will get checked with a magnet first. BTW, these are all 1% or better...
Thanks for the kind thoughts. It was a fun time and great learning experience.
Saw that you have a patent involving linear phase power in supplies. I've found that linear phase
is very important in audio electronics. Can you list your US patent number?
Found the application.
Output Impedance Compensation for Voltage Regulators
is very important in audio electronics. Can you list your US patent number?
Found the application.
Output Impedance Compensation for Voltage Regulators
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Maybe there is a reason they are scrap.
Why would anybody pull old - used -overheated - stumps (you can´t call those "legs") parts for new builds stinks of magic- make_believe - TOC - nonsense ; pick one or more.
The worry about "magnetism" is the cherry on the cake.
Maybe the Mojo associated with old respected Brands will rub on your new projects?
"Hey, this amp/preamp was made with HP - Wavetek - Tektronix parts!!!!" Wow!!!!
Builder pride DEFINITELY plays a part on this 😉
But nothing which can pass a double blind test.
Here, I m not even suggesting *measuring* anything, since you SO MUCH despise it 😉
So you claim a non magnetic resistor will sound different than a normal one?
Gimme a break!!!!
The problem with second hand pcb's is its likely they have been scrapped because something failed.
How do you know the salvaged resistor hasnt failed without testing every one ?
I pay 2p £0.02GBP for a resistor so salvaging is wasting my time and money.
I get mine from a RS Components who are a very reputable dealer.
How do you know the salvaged resistor hasnt failed without testing every one ?
I pay 2p £0.02GBP for a resistor so salvaging is wasting my time and money.
I get mine from a RS Components who are a very reputable dealer.