GRollins said:
Actually, the tone controls are on the backside...
and, if you look closely there are spacers between the top cover and the case because of my optimisum that it would all fit was misguided. The current I use is based on the application, I dial it in to match.
Unfortunately I just bought a pile of FETs and now I'll need to figure out how it works, again. I know I have a schematic somewhere...
Mike.
Does anyone know how to purchase very small self sealing bags? My former tech bought the ones that I have here, and I have never sourced them. They ARE perfect for TO-92 devices, and are relatively tough, so they don't puncture too easily. Even if they do puncture, and 1 or 2 devices escape, it is easy to find where they came from, because of the puncture in the bag. One of the advantages of these little bags is that they lay flat against each other, saving space. You could put 1000 devices under your mattress and not be bothered. If you have unmeasured devices, you can put them in a ' ? ' bag that can be sorted later, or used one at a time for a current source (with a series resistor), etc.
If you have unmeasured devices, you can put them in a ' ? ' bag that can be sorted later, or used one at a time for a current source (with a series resistor), etc.
Magura,
Your parts have never gotten mixed on the bench while you're building a prototype and trying different Vgs values, etc? You're a lucky fella.
apassgear,
As far as I know, we are all aging at the same rate. If I'm pulling ahead, then perhaps I should see if there have been any modifications to the Lorentz contraction equations that allow time to advance faster here than in other places. I mean, I know that I move slowly, but I didn't realize that the difference was sufficient to be relativistically significant.
Mike,
And I thought I was the only one who ever had to find old schematics in order to know what/how something did what it did.
John,
Don't get me wrong. I have a dedicated space for electronics for the first time in my life and I think that's really nifty. Finally, I've got somewhere to stack all the stuff and junk and things and whatnots that I've accumulated over the years.
I was wasting space with a lot of pieces of equipment that I wanted to salvage gizmos from, but never seemed to get around to doing so. (We all know that John would never keep stuff like that, but I'll bet the rest of you know what I'm talking about.) A while back, I declared a "Melt-down day" whereupon I girded my loins and attacked all those space-wasters, thus producing a pretty hefty pile of refuse and an embarassingly small pile of goodies. (Oh, to think of the energy I wasted carrying that nonsense around over the years.) Once the junk was carted off, I had space to walk...for about a month. A few survivors of the first Melt-down day have since crept out of hiding. I'm piling them up. Their time is coming...just as soon as I change this diaper, finish the amp I'm working on, feed the twins, prototype the phono stage I've been scratching on paper for the last month, harvest the peppers...okay, so maybe those old circuits aren't exactly cringing in fear. They know full well that they've got at least another decade to live at the rate things are going.
If the small ziplock bags are what you want, let me know and I'll send you a zillion or so. My wife works at a locksmith's shop and they get scads of the things with keys, pins, screws, you name it in them. I'm currently using a few of them to hold my remaining stock of Lovoltech JFETs, so it's not as though I'm unacquainted with the concept. I just stick a scrap of paper in the bag with Vgs and quantity so I can keep track of stock. They just don't work so well when I'm in and out of the bags, actively messing with the parts. But for stock...oh yeah, they're great.
Grey
Your parts have never gotten mixed on the bench while you're building a prototype and trying different Vgs values, etc? You're a lucky fella.
apassgear,
As far as I know, we are all aging at the same rate. If I'm pulling ahead, then perhaps I should see if there have been any modifications to the Lorentz contraction equations that allow time to advance faster here than in other places. I mean, I know that I move slowly, but I didn't realize that the difference was sufficient to be relativistically significant.
Mike,
And I thought I was the only one who ever had to find old schematics in order to know what/how something did what it did.
John,
Don't get me wrong. I have a dedicated space for electronics for the first time in my life and I think that's really nifty. Finally, I've got somewhere to stack all the stuff and junk and things and whatnots that I've accumulated over the years.
I was wasting space with a lot of pieces of equipment that I wanted to salvage gizmos from, but never seemed to get around to doing so. (We all know that John would never keep stuff like that, but I'll bet the rest of you know what I'm talking about.) A while back, I declared a "Melt-down day" whereupon I girded my loins and attacked all those space-wasters, thus producing a pretty hefty pile of refuse and an embarassingly small pile of goodies. (Oh, to think of the energy I wasted carrying that nonsense around over the years.) Once the junk was carted off, I had space to walk...for about a month. A few survivors of the first Melt-down day have since crept out of hiding. I'm piling them up. Their time is coming...just as soon as I change this diaper, finish the amp I'm working on, feed the twins, prototype the phono stage I've been scratching on paper for the last month, harvest the peppers...okay, so maybe those old circuits aren't exactly cringing in fear. They know full well that they've got at least another decade to live at the rate things are going.
If the small ziplock bags are what you want, let me know and I'll send you a zillion or so. My wife works at a locksmith's shop and they get scads of the things with keys, pins, screws, you name it in them. I'm currently using a few of them to hold my remaining stock of Lovoltech JFETs, so it's not as though I'm unacquainted with the concept. I just stick a scrap of paper in the bag with Vgs and quantity so I can keep track of stock. They just don't work so well when I'm in and out of the bags, actively messing with the parts. But for stock...oh yeah, they're great.
Grey
My sorting jig ain't as pretty (?) as Mike's (a PCB with spacer legs), but it's the same general idea. I have 5 sockets, which cover all the Jfets and small signal Mosfets I'm inclined to use, with pin sockets to plug in a pair of DVMs for VGS and drain current. My jig runs off a pair of 9V batteries.
I used to match parts in advance according to IDSS, rope the parts together with tape, and mark the measured values on the tape. Now
I match on demand by starting with a pile of fets and a piece of paper. Each fet gets a space on the paper with measured VGS at the ID of interest, and I use this info to put pairs together. I generally won't accept a match looser than 0.010 volt. It helps that I don't have cats or kids....
I used to match parts in advance according to IDSS, rope the parts together with tape, and mark the measured values on the tape. Now
I match on demand by starting with a pile of fets and a piece of paper. Each fet gets a space on the paper with measured VGS at the ID of interest, and I use this info to put pairs together. I generally won't accept a match looser than 0.010 volt. It helps that I don't have cats or kids....
A stack of paper envelopes, standing upright in a box of the same size, keeps them tidy and easy to catch.
The Idss number is written on the envelope and they're closed with a paperclip.
Glueing a piece of xerox paper on anti-static foam of the same size keeps the parts safe in position, piccy=>
The Idss number is written on the envelope and they're closed with a paperclip.
Glueing a piece of xerox paper on anti-static foam of the same size keeps the parts safe in position, piccy=>
Attachments
Hi Jacco,
I do the same thing that you do, except that I put them in drawers. Large amounts go in a bag together (one number to bag) and I sit down and sort some every now and again. Works for me.
Hi Grey,
-Chris
I do the same thing that you do, except that I put them in drawers. Large amounts go in a bag together (one number to bag) and I sit down and sort some every now and again. Works for me.
Hi Grey,
Yes. This becomes a balance between how much your time is worth and what the parts are worth.
-Chris
There is easy, there is cheap, and there is the mass production way.
I have pointed out one easy (low instrument cost) and efficient way to sort and store parts.
In production, we usually have a special test jig, that is essentially composed of a test socket, meter and power supply. This makes selection faster, even when you get bored with the process. Test over 50 parts, and this makes sense.
I have also specified that Idss is a good way to measure. The reason is that two of the same device type with the same APPROXIMATE Idss work pretty well together in most circuits. You can be 1ma or even 2 ma off in some circuits, without too much problem. The real problems is when you have a 3 ma device and try to match it with a 13 ma device. This rarely works.
When it comes to complementary differential, it is the similar parts that need the most matching. N-N, P-P. A reasonable difference, maybe 5ma, can be tolerated between N and P pairs. The single resistor between the pairs tends to compensate for the differences, and forces a compromise.
I have pointed out one easy (low instrument cost) and efficient way to sort and store parts.
In production, we usually have a special test jig, that is essentially composed of a test socket, meter and power supply. This makes selection faster, even when you get bored with the process. Test over 50 parts, and this makes sense.
I have also specified that Idss is a good way to measure. The reason is that two of the same device type with the same APPROXIMATE Idss work pretty well together in most circuits. You can be 1ma or even 2 ma off in some circuits, without too much problem. The real problems is when you have a 3 ma device and try to match it with a 13 ma device. This rarely works.
When it comes to complementary differential, it is the similar parts that need the most matching. N-N, P-P. A reasonable difference, maybe 5ma, can be tolerated between N and P pairs. The single resistor between the pairs tends to compensate for the differences, and forces a compromise.
I used to buy only what I needed to complete a given project. That's easy if you're doing a paint-by-numbers circuit where you're working from a schematic of a proven circuit, but not as effective when you're developing circuits from scratch. Once I got serious about new circuits, I began buying parts by the hundred. Not coincidentally, that's about the same time I got serious about storage. I used to buy the cheap plastic drawers, but got fortunate and bought a bunch of "real" parts bins when the parts store went out of business. Time is my most precious commodity and I can't afford to waste a single minute. I'm lucky if I get twenty minutes to work on a circuit. If I spend fifteen of those minutes having to dork with parts, I might as well just give up for the day--I can't even get things turned on and warmed up in five minutes. If drawers can cut my time overhead down to one or two minutes, it's a no-brainer. The alternative is getting nothing done at all and that's unacceptable.
I keep meaning to whip up a circuit similar to the one Mike posted above, but never seem to get it done. Given that anything like the Blowtorch requires matched parts, there's more to it than just plucking parts out of a box at random. Particularly when you have to buy in bulk so as to have a pool of parts to seek matches in.
Grey
I keep meaning to whip up a circuit similar to the one Mike posted above, but never seem to get it done. Given that anything like the Blowtorch requires matched parts, there's more to it than just plucking parts out of a box at random. Particularly when you have to buy in bulk so as to have a pool of parts to seek matches in.
Grey
If I may share my own experience with you on JFET matching.
Within the few years I am doing DIY audio, I have probably measured over a thousand JFETs. Initially I also did what everyone did -- measure Idss. And I was lazy and used to only measure one transistor in a matched pair (2SK389 / 2SJ109). Until I got myself a PC scope with functions generator, and I started testing them from 0.1mA to Idss.
And to my surprise, not an insigificant portion of 2SK389/2SJ109's are outside the 3% matching spec. And even the majority have close to identical Idss, there are still examples amongst those where one FET has a higher transconductance than the other, and thus the Id vs Vgs curves of the two FETs only match at 1 point. Of course there are also examples where they match over the entire range within 0.5%.
So for those who has a functions generator and a scope, I strongly recommend measuring over the entire working range. It takes me 5 minutes to set up, and then it is as easy as measuring with a multimeter (using a socket). It takes less than an hour to measure 50 FETs. Of course the data evaluation takes longer afterwards.
Patrick
Within the few years I am doing DIY audio, I have probably measured over a thousand JFETs. Initially I also did what everyone did -- measure Idss. And I was lazy and used to only measure one transistor in a matched pair (2SK389 / 2SJ109). Until I got myself a PC scope with functions generator, and I started testing them from 0.1mA to Idss.
And to my surprise, not an insigificant portion of 2SK389/2SJ109's are outside the 3% matching spec. And even the majority have close to identical Idss, there are still examples amongst those where one FET has a higher transconductance than the other, and thus the Id vs Vgs curves of the two FETs only match at 1 point. Of course there are also examples where they match over the entire range within 0.5%.
So for those who has a functions generator and a scope, I strongly recommend measuring over the entire working range. It takes me 5 minutes to set up, and then it is as easy as measuring with a multimeter (using a socket). It takes less than an hour to measure 50 FETs. Of course the data evaluation takes longer afterwards.
Patrick
I just got a new MCM catalog today. They still seem to sell 2SK170, and 2SJ74 devices. Each device is priced at under $1 ea. Is this really a high price to pay? Please, don't waste my time, if you balk at this opportunity.
One could buy 25ea and get them sent anywhere in the USA for less than $50. Then you can sort them with your RS voltmeter, and store them in any package you want. Because these are Japanese parts, you can expect a fairly tight spread in the Idss, whatever they offer you. Less than 3 to one. Now, is this so difficult?
Now, in Europe, you might contact Borbely for your parts.
One could buy 25ea and get them sent anywhere in the USA for less than $50. Then you can sort them with your RS voltmeter, and store them in any package you want. Because these are Japanese parts, you can expect a fairly tight spread in the Idss, whatever they offer you. Less than 3 to one. Now, is this so difficult?
Now, in Europe, you might contact Borbely for your parts.
I don't have a problem with their pricing, but the last time I ordered from MCM, I got GR parts. For some circuits it matters. For some it doesn't. For me it usually does since I like to push things as hard as possible.
And no, they wouldn't tell me what they had in stock ahead of time. It was catch as catch can. In fact, I have yet to find a place that will tell you whether they have GR/BL/V in stock. You order. The truck comes. You get a surprise. Sometimes good, sometimes not so good.
Actually, I've never gotten V. That would be a nice surprise.
Grey
And no, they wouldn't tell me what they had in stock ahead of time. It was catch as catch can. In fact, I have yet to find a place that will tell you whether they have GR/BL/V in stock. You order. The truck comes. You get a surprise. Sometimes good, sometimes not so good.
Actually, I've never gotten V. That would be a nice surprise.
Grey
Hi John,
Yes, the 2SJ74 (who knows what rank) will be $0.98 US in a 25 lot, 1.11 in 10 lots (10 lots are for the home DIY guy). The 2SK170 (whatever) is more reasonable at $0.77 USD in 25 lots and 0.81 in 10 lots.
You know what? I've been spoiled by low prices earlier in time. What bugs me is that I did lay in a good stock of those numbers and more. They went with the shop. Now, the prices are a bit high for many average people. No choice now but to design without them.
I could take the same stance as you, John. I don't because I do understand the average guy just as I understand market forces. I must admit that I am use to knowing exactly what I am buying before I lay my money down. How hard is it to indicate the device rank? Yeah, that's a question for MCM.
Show a little compassion for your fellow man. I guess that's all I'm saying here.
-Chris
Yes, the 2SJ74 (who knows what rank) will be $0.98 US in a 25 lot, 1.11 in 10 lots (10 lots are for the home DIY guy). The 2SK170 (whatever) is more reasonable at $0.77 USD in 25 lots and 0.81 in 10 lots.
You know what? I've been spoiled by low prices earlier in time. What bugs me is that I did lay in a good stock of those numbers and more. They went with the shop. Now, the prices are a bit high for many average people. No choice now but to design without them.
I could take the same stance as you, John. I don't because I do understand the average guy just as I understand market forces. I must admit that I am use to knowing exactly what I am buying before I lay my money down. How hard is it to indicate the device rank? Yeah, that's a question for MCM.
Show a little compassion for your fellow man. I guess that's all I'm saying here.
-Chris
GRollins said:
I purchase most of my Japanese parts from www.bdent.com Perhaps not the cheapest around, but very reliable and well stocked. They have 2SK170/2SJ74 in stock and you can order GL/BL/V to your choice. They ship via USPS (pretty cheap) or if you shell $25 you can have your parts next day via UPS courier.
- Status
- Not open for further replies.