Hi John,
I just spend some money on parts (couple hundred). Of course, more than I need now. I am very well stocked for many things also. The point that Grey has made is that most of us can not do what you do. I couldn't really afford to buy those parts, but I did. Grey has done the same also and was hit with the bomb that plagued US part manufacture. Part variability. It would help if the listed specs were more truthful.
Only recently has On Semi got their processes under control for semiconductors. Before that time I bought tons of parts to pick through and used the rest up the best I could in non-critical locations. I miss those Carver amps where I could use "flyers" up as commutators. Now, every one of them represents cash lost.
In a perfect world, we could all commit whatever cash was required to our hobby. It's far from a perfect world and many of us have wives that watch our spending also.
Grey, I do feel your pain here. Similar things have happened to me more than once.
-Chris
I just spend some money on parts (couple hundred). Of course, more than I need now. I am very well stocked for many things also. The point that Grey has made is that most of us can not do what you do. I couldn't really afford to buy those parts, but I did. Grey has done the same also and was hit with the bomb that plagued US part manufacture. Part variability. It would help if the listed specs were more truthful.
Only recently has On Semi got their processes under control for semiconductors. Before that time I bought tons of parts to pick through and used the rest up the best I could in non-critical locations. I miss those Carver amps where I could use "flyers" up as commutators. Now, every one of them represents cash lost.
In a perfect world, we could all commit whatever cash was required to our hobby. It's far from a perfect world and many of us have wives that watch our spending also.
Grey, I do feel your pain here. Similar things have happened to me more than once.
-Chris
Mind you, both the J310s and the J271s were within their respective specs, it's just that the specs aren't a 1:1 overlap and the J271s fell near the bottom of their range, which happens to be the end that doesn't overlap the J310.
Oh, well.
John,
Oh, trust me, I'm quite pleased to have so many matched pairs...triplets...quads...hell, I could run twenty or forty J271s in parallel and probably achieve something magical...if only I had J310s to operate in opposition. As it is, lacking sufficient complements, and lacking Idss N-ch matches, I've got near-useless parts unless I want to build a single-ended P-ch follower/P-ch CCS--something along the lines of Nelson's Zen circuit, or maybe a miniature New-Tron.
I normally buy parts by the hundred these days, simply because I match parts and frequently build multiple variations of circuits I come up with. I'm hard pressed to see how these little boogers will ever earn their keep, though. Even if I used a half-dozen in every circuit I ever build, I've got several lifetimes' supply.
Bummer.
Grey
Oh, well.
John,
Oh, trust me, I'm quite pleased to have so many matched pairs...triplets...quads...hell, I could run twenty or forty J271s in parallel and probably achieve something magical...if only I had J310s to operate in opposition. As it is, lacking sufficient complements, and lacking Idss N-ch matches, I've got near-useless parts unless I want to build a single-ended P-ch follower/P-ch CCS--something along the lines of Nelson's Zen circuit, or maybe a miniature New-Tron.
I normally buy parts by the hundred these days, simply because I match parts and frequently build multiple variations of circuits I come up with. I'm hard pressed to see how these little boogers will ever earn their keep, though. Even if I used a half-dozen in every circuit I ever build, I've got several lifetimes' supply.
Bummer.
Grey
GR - one thing you wanna look out for is that part numbers have been altered due to the lead-free uproar. I thought that Mouser had stopped stocking the Vishay PN4393, one of my favorite JFETs for just mucking around. It turns out that they have it, but the P/N is modified with a no-lead prefix, which made it hard for the search engine to find what I was looking for. Perhaps it's the same deal with the J310.
Having said that, my next buy of JFETs will be a large one, as they seem to be an endangered species.
Having said that, my next buy of JFETs will be a large one, as they seem to be an endangered species.
wrenchone said:
See my above post #2077. Getting the Fairchild part isn't a problem. They're common as grass.
wrenchone said:
Uh, unh...no way. Look at the Idss for those parts. Huge range. I just about guarantee you that I'd end up with something out of range for the J310s again. The last thing I need is more P-ch JFETs that I can't use. Besides, how would you test Idss on a TO-92 case with 135mA, but only 350mW Pd? You're at maximum dissipation at 2.5V. Yikes.
You want to know something really scary? I just went to Vishay/Siliconix and they no longer list the J270/J271. Does anyone know whether they've divested the part or is it simply gone?
The J310 and siblings are still listed, for what it's worth.
The ticket would be to find some J304 N-ch, which spec 5-15mA Idss and hope to match my J271s against those, but they are...you guessed it...unobtainium...even though they still show on the Vishay/Siliconix website. Anyone know where to find some?
Grey
Hmm - I sort by Vgs at a given drain current. I have a jig set up so that I can look at just about any common JFET or small signal MOSFET at switch selectable drain currents of 1,2,5,or 10 ma current,which covers just about all situations of interest to me. I'm working on a simpler jig where the current sources for test are continuously adjustable, so I can sort using just about any drain current within reason. If I get a little time, I'll try looking at typical Vgs values at 5mA in my stash of J310s, J175s, and J176s, as well as some J113s I have around. and report the spread I find.
I have an ulterior motive anyway, as I have an amp partially built up that was the result of some discussion on another thread regarding JC's amps. I'm trying to decide at this point whether I want to stuff the inputs with the usual Japanese suspects. or some older devices with lower transconductance. I've been eyeing my stash of J310s for some time, but was thinking more of using them in a unipolar differential input.
I have an ulterior motive anyway, as I have an amp partially built up that was the result of some discussion on another thread regarding JC's amps. I'm trying to decide at this point whether I want to stuff the inputs with the usual Japanese suspects. or some older devices with lower transconductance. I've been eyeing my stash of J310s for some time, but was thinking more of using them in a unipolar differential input.
john curl said:
Unfortunately, it is. The Vishay/Siliconix website lists four distributors--none of whom seem inclined to actually stock the parts.
From this point forward, I can either try to find parts to match the J310s, which "should" have been the J271, or I can try to find parts to match the J271s, in which case it looks as though the J304 is my best bet judging from the Idss specs (not a perfect overlap there, either). But no one seems to carry J304s.
You'd think their distribution would be better than it is, but it's about like trying to find Toshiba parts.
Grey
Your search for parts is still pretty limited. IF you want to play, you have to pay. That's life. Just remember that just one tire on a new Porsche will set you back at least $500. And that is with no guarantee for road hazards. In perspective, fets are still cheap, just more expensive that they used to be.
For most anyone who wants to work with jfets:
I recommend trying to get Toshiba single parts, first. The reason is that they are still somewhat available, low noise, high Gm, and good complements.
You should always get more than you are going to use for one project. Think about it like you would think about ordering solder. You don't buy it by the meter length, do you? You usually buy it by the pound or something similar. It is still there and useful when you want to make your next project.
it is the same with fets. T0-92 size fets take very little space. You can probably put 100 in the palm of your hand. Storage? A plastic bag does perfectly.
IF you own a multimeter, you can easily sort and match your fets. I usually sort them into separate plastic bins, but you can use tiny plastic bags just as easily. Just mark the Idss that you measure on the outside of the bag(s). You can then put them all into a larger plastic bag and put them into a drawer.
Measuring Idss takes a multimeter (doesn't have to be a very good one), a 1 to 10 ohm resistor, and a nine volt battery. A transistor socket makes it easier, but clip leads will work just as well.
All you do is short out the gate to one of the other leads and set it to ground. Then to the extra lead you attach to a 10 ohm resistor and to the other end of the resistor, you put the 9V battery. You then clip lead the voltmeter terminals across the 10 ohm resistor.
If you get you battery polarity right, then you will read the Idss of the fet from the reading of the voltmeter, divided by the resistor value.
For example, if you are measuring a fet and 0.2V is read on the voltmeter, then you have an Idss of 20ma. You put it into a small plastic bag reading 20ma.
Then the next fet might read .15V. This would be 15ma Idss, so you would use another small bag and label it 15ma. It is that easy. Of course, if you measure a device and it is 14.5ma, you might put it in the 15 ma bag, because it is close enough to work as a pair. I have hundreds of these little bags in my lab. This is how it is done. Is this so complex or difficult? Once you have enough matched pairs, you can work on their complements by simply reversing the battery. After a while, you have a whole group of complementary differential matched pairs that you can use. You may have some odd values too, but they can be useful for current sources, or even low noise series pass cap multipliers. I use them this way every day.
I recommend trying to get Toshiba single parts, first. The reason is that they are still somewhat available, low noise, high Gm, and good complements.
You should always get more than you are going to use for one project. Think about it like you would think about ordering solder. You don't buy it by the meter length, do you? You usually buy it by the pound or something similar. It is still there and useful when you want to make your next project.
it is the same with fets. T0-92 size fets take very little space. You can probably put 100 in the palm of your hand. Storage? A plastic bag does perfectly.
IF you own a multimeter, you can easily sort and match your fets. I usually sort them into separate plastic bins, but you can use tiny plastic bags just as easily. Just mark the Idss that you measure on the outside of the bag(s). You can then put them all into a larger plastic bag and put them into a drawer.
Measuring Idss takes a multimeter (doesn't have to be a very good one), a 1 to 10 ohm resistor, and a nine volt battery. A transistor socket makes it easier, but clip leads will work just as well.
All you do is short out the gate to one of the other leads and set it to ground. Then to the extra lead you attach to a 10 ohm resistor and to the other end of the resistor, you put the 9V battery. You then clip lead the voltmeter terminals across the 10 ohm resistor.
If you get you battery polarity right, then you will read the Idss of the fet from the reading of the voltmeter, divided by the resistor value.
For example, if you are measuring a fet and 0.2V is read on the voltmeter, then you have an Idss of 20ma. You put it into a small plastic bag reading 20ma.
Then the next fet might read .15V. This would be 15ma Idss, so you would use another small bag and label it 15ma. It is that easy. Of course, if you measure a device and it is 14.5ma, you might put it in the 15 ma bag, because it is close enough to work as a pair. I have hundreds of these little bags in my lab. This is how it is done. Is this so complex or difficult? Once you have enough matched pairs, you can work on their complements by simply reversing the battery. After a while, you have a whole group of complementary differential matched pairs that you can use. You may have some odd values too, but they can be useful for current sources, or even low noise series pass cap multipliers. I use them this way every day.
wrenchone said:
I've been waiting to see if there were any other comments on this. I do the same, I pretty much know what current I want to run and have a jig I built many years ago that lets me flip through and note IDSS, the pinch off IDSS and same at the the current I plan to run them.
I reason that this is important if I want the N and P-channels to respond in a similar manner.
Mike.
Attachments
Good grief, Mike...you forgot the tone controls.
(Next time use a bigger project box. How the dickens do you get your fingers in there?)
I rarely use a pre-chosen current. The current I use is generally dictated by the circuit rather than vice versa. It's easy enough to measure Idss and at least as versatile.
I remember a post by Karen (once a member of the Pass Labs crew--since gone on to other endeavors) in a thread regarding matching of devices. People were talking about ways to keep track of matched devices. She posted something to the effect of, "Well, you silly guys, obviously all you have to do is put them in separate drawers!"
And let them eat cake, too, while you're at it.
Obviously she hadn't priced parts drawers recently, which is fine as long as Nelson's buying. Even the cheap little P.O.S. 60 drawer units at Lowe's were over $20 the last time I priced them and that's been a couple of years. (Be sure to inspect them carefully before buying. They nearly always have broken drawers.) If you've got any number of parts to store, you're going to drop money that would probably be better spent on parts. The better drawers cost real money. I got lucky and snatched up a lot of parts drawers when my favorite local parts house went out of business a couple of years ago. I miss them, but am glad to have the drawers.
Bags are fine. Bags are cheap. Bags are quick and easy. I've got some stuff in bags. But my problem is that I can never find the confounded bag I want. It's always slithered its way into some forgotten corner. And every once in a while the seam splits, which can really make life difficult.
My problem is that I've got a 6' wide by 14' long space that also has to hold transformers (well over 100, ranging from several bigger than my head down to little-bitty ones), caps (electrolytics eat up space fast), resistors, heat sinks, tubes, semiconductors, circuits, etc. John, I wish I had the equivalent square footage of your 'small apartment.' I barely have room to walk. Oh, yeah...don't forget the water heater, my punching bag from karate days, mic stands from back when I played in bands, a monster duct coming out of the heat pump at knee height which goes up to the ceiling, and of course the test equipment, most of which is in a six foot rack in the middle of the floor. At least I got smart and put wheels on the rack so I could move it...or at least I could up until I hemmed it in with stuff, mostly books and heat sinks. Fortunately, most of my books live upstairs.
Incidentally, keeping parts in drawers, bags, whatever, works great as long as they're just sitting around, but once you pull them out of the drawer, they look just like any of their kin. I use a dab of White-out on the case, then write either the characteristic that's important to me or a number that I can look up in a spreadsheet that has all the pertinent info for that device. Otherwise, you're going to waste time retesting in order to figure out which drawer they go back into at the end of the day.
Yes, if they're TO-92s it takes a steady hand and small numbers--but better to spend the time once than to do it over and over through the years.
Grey
(Next time use a bigger project box. How the dickens do you get your fingers in there?)
I rarely use a pre-chosen current. The current I use is generally dictated by the circuit rather than vice versa. It's easy enough to measure Idss and at least as versatile.
I remember a post by Karen (once a member of the Pass Labs crew--since gone on to other endeavors) in a thread regarding matching of devices. People were talking about ways to keep track of matched devices. She posted something to the effect of, "Well, you silly guys, obviously all you have to do is put them in separate drawers!"
And let them eat cake, too, while you're at it.
Obviously she hadn't priced parts drawers recently, which is fine as long as Nelson's buying. Even the cheap little P.O.S. 60 drawer units at Lowe's were over $20 the last time I priced them and that's been a couple of years. (Be sure to inspect them carefully before buying. They nearly always have broken drawers.) If you've got any number of parts to store, you're going to drop money that would probably be better spent on parts. The better drawers cost real money. I got lucky and snatched up a lot of parts drawers when my favorite local parts house went out of business a couple of years ago. I miss them, but am glad to have the drawers.
Bags are fine. Bags are cheap. Bags are quick and easy. I've got some stuff in bags. But my problem is that I can never find the confounded bag I want. It's always slithered its way into some forgotten corner. And every once in a while the seam splits, which can really make life difficult.
My problem is that I've got a 6' wide by 14' long space that also has to hold transformers (well over 100, ranging from several bigger than my head down to little-bitty ones), caps (electrolytics eat up space fast), resistors, heat sinks, tubes, semiconductors, circuits, etc. John, I wish I had the equivalent square footage of your 'small apartment.' I barely have room to walk. Oh, yeah...don't forget the water heater, my punching bag from karate days, mic stands from back when I played in bands, a monster duct coming out of the heat pump at knee height which goes up to the ceiling, and of course the test equipment, most of which is in a six foot rack in the middle of the floor. At least I got smart and put wheels on the rack so I could move it...or at least I could up until I hemmed it in with stuff, mostly books and heat sinks. Fortunately, most of my books live upstairs.
Incidentally, keeping parts in drawers, bags, whatever, works great as long as they're just sitting around, but once you pull them out of the drawer, they look just like any of their kin. I use a dab of White-out on the case, then write either the characteristic that's important to me or a number that I can look up in a spreadsheet that has all the pertinent info for that device. Otherwise, you're going to waste time retesting in order to figure out which drawer they go back into at the end of the day.
Yes, if they're TO-92s it takes a steady hand and small numbers--but better to spend the time once than to do it over and over through the years.
Grey
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