BJTs being phased out? - Page 1
Forum section: electronics / general

author: eti
author_rank: Super Contributor
timestamp: October 13, 2020, 02:50:03 am
content: I'm watching an electronics fundamentals lecture series, and the tutor seemed to be implying that BJTs are being phased out; he said "BJTs are slowwwwwly being replaced by MOSFETS" ... or maybe I've put words into his mouth through misinterpreting what he said...Is this the case? I find it extremely hard to believe.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 13, 2020, 04:40:14 am
content: I wonder if the statement might be a misquote of a more quantitative one: MOSFETs surpass BJTs, in terms of number of transistors produced. A change which occurred, what, back in the 70s, early 80s?Back in the 70s, 7400 and LS TTL were still king for medium-high speed, board-level logic, and computing (and also ECL for the highest speeds). Meanwhile, MOS ranging from metal-gate CD4000 family, to NMOS and CMOS VLSI, took off massively, and never turned back. (VLSI = Very Large Scale Integration, thousands of transistors per die.) A single 8080 probably contains as many MOSFETs as a large card of 7400 (SSI scale) gates?BJTs were never able to integrate quite as well, whether due to heat dissipation (that card of TTL would dissipate a couple ten watts, easily) or, Idunno, signal quality issues and design complexity? (There was an Integrated Injection Logic, which uses open-collector outputs fanning in to current-sourced inputs; it's completely upside-down to design with, because there's only fan-in, no fan-out to speak of. Signal levels are around a Vbe, so, would be quite sensitive to noise by itself.)BJTs have been displaced in analog and mixed-signal spaces, too. I'm... not sure offhand what would be an example "breakthrough" shift to MOS, but there are lots of op-amps and such, mostly in lower voltage families, where mature CMOS (feature size ~200nm) dominates in affordable performance: higher bandwidth per supply current, greater functionality and integration (not just rail-to-rail inputs and outputs, but feed-forward techniques, precision auto-zero and chopper types), etc. (The feature size is relevant for two reasons: one, it's cheap of course; but two, it also performs better than bleeding-edge processes do. That's right, the transistors in a modern CPU actually perform worse, pound for pound so to speak; they're justso much smallerthat they can get away with much higher frequencies (but not proportionally higher!) and much higher integration density.)Commodity RF applications have been monolithic for some time. These are mixed-signal designs, including DSPs and high speed ADCs/DACs, as well as analog processing (filtering, mixing, PLLs, amps, etc.). They even use integrated inductors and transformers, in the higher frequency parts (>1GHz) -- crummy ones, but good enough to be useful! And these are all MOS, as far as I know.Even so, there are some newer applications of BJTs, or similar devices anyway. Many fabs use a SiGe process for advanced op-amps. These devices have even better transconductance and capacitance, allowing even higher bandwidth per supply current, without sacrificing the input noise that CMOS tends to have, nor being restricted to low voltages.Huh, I seemed to recall SiGe ICs were kind of an oddball or new thing, about a decade ago. Checking press releases, it looks like at least TI, LT and ADI (this was before the latter two merged) introduced parts with this process in 2006-2010. So it looks to be just another quiet innovation these days; you might never realize your op-amp contains germanium!Tim

author: magic
author_rank: Super Contributor
timestamp: October 13, 2020, 07:17:14 am
content: ^ A common occurrence in academia, and it affects all industries

author: tooki
author_rank: Super Contributor
timestamp: October 13, 2020, 08:36:23 am
content: Quote from: MasterTech on October 13, 2020, 06:34:44 amExcept that the instructor is basically correct: as others explained above, the MOSFEThasbeen displacing the BJT in many applications, and if we include the transistors embedded in ICs, then the MOSFET won ages ago, thanks to each of us owning many billions of them in our processors. Percentage wise, the MOSFET undoubtedly makes up the vast majority of transistors manufactured today.I only take issue with the wording “phase out”, which implies a premeditated, scheduled abandonment; that certainly isn’t the case. It’s just natural evolution of designs as the components themselves evolve. For example, one reason we can make modern, efficient switch mode power supplies is because of modern, efficient, low RDSonMOSFETs. So that contributed to the abandonment of linear power supplies (whose pass transistors, whether discrete or embedded in a regulator IC, are generally BJTs). Audio amplifiers (save for those in discrete hi-fi amplifiers) have largely switched to switching topologies as well, powered by... MOSFETs.

author: richard.cs
author_rank: Super Contributor
timestamp: October 13, 2020, 09:39:29 am
content: Quote from: tooki on October 13, 2020, 08:36:23 amAgreed, phase out to me also implies an eventual complete removal. This is essentially not going to happen with BJTs. As I see it there are a number of applications that pretty much only work with BJTs, a number that pretty much only work with fets, and then a huge swathe in the middle where either could be used and within that area there's been a long-term drift from bipolar to fets.

author: OwO
author_rank: Super Contributor
timestamp: October 13, 2020, 11:05:27 am
content: No. Show me a FET based MMIC that can give you flat response (let's say within 6dB) to 5GHz and has reasonable noise figure. BGA616 fits the bill and it's BJT based.

author: tooki
author_rank: Super Contributor
timestamp: October 13, 2020, 12:59:03 pm
content: Quote from: OwO on October 13, 2020, 11:05:27 amGiven the nature of the original post, I don't think the OP is knowledgeable enough about microwave electronics to be able to answer your question.I think the rest of the thread already characterizes the situation well, which richard.cs's comment sums up perfectly:Quote from: richard.cs on October 13, 2020, 09:39:29 am

author: coppice
author_rank: Super Contributor
timestamp: October 13, 2020, 01:46:20 pm
content: I think we pretty much reached an equilibrium some time ago, where anything digital and quite a lot of analogue things use MOSFETs and some analogue things use BJTs. There are some exceptions where BJTs are still king for a switching application. If you want a cheap 1200V transistor as a primary switch in an SMPS that can sit across 3-phase mains, for example, BJTs are king.

author: tooki
author_rank: Super Contributor
timestamp: October 13, 2020, 02:11:22 pm
content: Aren't those all shifting to IGBTs? I mean, an IGBT is essentially a hybrid of the two, so the real answer is even more complex!

author: tooki
author_rank: Super Contributor
timestamp: October 13, 2020, 03:12:35 pm
content: Thanks for the added info! In that case, what's the IGBT's advantage that's leading to their increased use in high-power applications?

author: coppice
author_rank: Super Contributor
timestamp: October 13, 2020, 03:17:50 pm
content: Quote from: tooki on October 13, 2020, 02:11:22 pm1200V IGBTs get expensive. For higher power levels they may be the better choice. However, low power 1200V BJTs are super cheap, so for low power supplies in a lot of 3 phase control, monitoring and metering applications they are a great choice. That market is big enough that there are SMPS controller chips specifically designed to drive a high voltage BJT. For single phase 240V work you have a lot more choices of good cheap transistors with adequate voltage headroom. This is just an example application. There are others where the price of a suitable MOSFET or IGBT starts to rise rapidly above about 700V, and a simple BJT is an excellent choice.

author: David Hess
author_rank: Super Contributor
timestamp: October 13, 2020, 08:14:52 pm
content: Just adding to your list:- Bipolar transistors have a higher transconductance than FETs. This also leads to a higher gain-bandwidth product.- Bipolar transistors have a higher current density than FETs, which leads to less area (cost) for a given current.- Bipolar transistors have a lower voltage noise than FETs.

author: Benta
author_rank: Super Contributor
timestamp: October 13, 2020, 08:17:09 pm
content: Quote from: eti on October 13, 2020, 02:50:03 amThis will happen the same day that the 555 gets phased out. According to most posts on this forum (from my feeling, every third), the 555 will cure Corona, world hunger, overpopulation and global warming as well as solve almost every electronic issue imaginable.Don't worry, the BJT will survive.I'm much more worried about the JFET, which is a dying species.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 13, 2020, 11:12:56 pm
content: There was a device called the "ESBT" (Emitter Switched Bipolar Transistor) many years back, it's literally just a high voltage bipolar transistor with a low voltage MOSFET in series with the emitter.Quote from: David Hess on October 13, 2020, 08:14:52 pmMOSFETs that can switch on the order of 100A are not that uncommon (they're found on every modern motherboard), but a 100A bipolar is pretty exotic.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 14, 2020, 12:55:18 am
content: Quote from: NiHaoMike on October 13, 2020, 11:12:56 pmNot exotic, just old. They reigned in motor drives and such, alongside SCRs, until IGBTs displaced them (in all but the biggest applications, where SCRs and GCTs still reign supreme). BJTs of 300A (or more?) and 1200V, often with triple-Darlington configuration, are common salvage items. I wouldn't call it "exotic", but "obsolete" is appropriate.Incidentally, ESBTs are still available (for exactly what applications, I do not know?), and they made a bit of a resurgence when SiC broke onto the market with JFETs and BJTs -- what's old is briefly new again, then old again as SiC MOSFETs and IGBTs were introduced.Tim

author: Benta
author_rank: Super Contributor
timestamp: October 14, 2020, 10:26:54 pm
content: @blueskull:I'm with you all the way in your description of JFET applications. They are wonderful devices.That doesn't change the fact that only very few are available today. Almost no major semiconductor manufacturers have them in their portfolio. And the ones that still have them are "pruning" their availability list.Today, only specialty manufacturers such as linearsystems.com supply a comprehensive line of JFETs, like the famous 2SJ74/2SK170.Like I said, it's a dying species.

author: LeoGray
author_rank: Newbie
timestamp: October 14, 2020, 11:56:45 pm
content: Quote from: blueskull on October 14, 2020, 01:48:07 amI never know JFET could be used for high voltage. I always want to make a electroadhesion thing that uses around 10KV. But never found a good cheap solution for discharging switch.Do you mind expending a little bit on the high voltage switching part? What's the buzz word I should search to find good articals and examples?Thanks in advance.

author: EEVblog
author_rank: Unknown
timestamp: October 15, 2020, 10:01:41 am
content: Quote from: Benta on October 13, 2020, 08:17:09 pmI'm feeling a Save the JFET T-Shirt coming on...

author: bsfeechannel
author_rank: Super Contributor
timestamp: October 15, 2020, 04:46:58 pm
content: Quote from: Benta on October 14, 2020, 10:26:54 pmThere's a discrete JFET inside every single electret microphone capsule. Maybe it is becoming a product for niche applications.Quote from: EEVblog on October 15, 2020, 10:01:41 amNot a bad idea. I've already rescued a bunch of stray JFETs off the streets and now they are happily living in my loving parts bin.

author: coppice
author_rank: Super Contributor
timestamp: October 15, 2020, 04:56:23 pm
content: Quote from: bsfeechannel on October 15, 2020, 04:46:58 pmTrue, but MEMS microphones are killing the market for electret microphones.

author: tszaboo
author_rank: Super Contributor
timestamp: October 15, 2020, 05:01:38 pm
content: Quote from: EEVblog on October 15, 2020, 10:01:41 amWe really should! Otherwise how do we make current mirrors to reflect on society.OP: BJT is cheaper than MOSFET so its not going anywhere.

author: tooki
author_rank: Super Contributor
timestamp: October 15, 2020, 06:20:47 pm
content: Quote from: coppice on October 15, 2020, 04:56:23 pmIs that true outside of severely space-constrained applications like cellphones and the mikes built into phone earpieces (be it inline in the cord or integrated like in AirPods)? I haven't gotten the impression that any other applications have embraced MEMS mikes.

author: coppice
author_rank: Super Contributor
timestamp: October 15, 2020, 06:31:46 pm
content: Quote from: tooki on October 15, 2020, 06:20:47 pmThat's 99% of all mics, isn't it? The electret mic market was mostly phones and cell phones. Phones have almost gone. Cellphones have moved to MEMS mics. Most other mics are condenser or dynamic. There were once some very high quality electret mics, but they seem to have gone, and now we only have condenser, ribbon and dynamic mics for high quality applications. Condenser mics also use a JFET, but their volumes are millions, not the hundreds of millions we see with cellphones.

author: tooki
author_rank: Super Contributor
timestamp: October 15, 2020, 06:34:29 pm
content: Quote from: coppice on October 15, 2020, 06:31:46 pmIn terms of sheer unit sales, perhaps. But other applications (like recording, stage and PA mikes, the ones in voice recorders, webcams, etc.) are hugely important and aren't going anywhere.

author: tooki
author_rank: Super Contributor
timestamp: October 15, 2020, 06:59:44 pm
content: Second reply after you edited to add everything that follows the single sentence quoted above.Quote from: coppice on October 15, 2020, 06:31:46 pmUhhhh… electret mikes were in practically every tape recorder. They're still widely used in webcams, laptops, and all manner of audio devices. They're still in every landline or VOIP phone and headset.Quote from: coppice on October 15, 2020, 06:31:46 pmAt home, yes, they're going that way. In businesses, not really. They may not be true circuit-switched landline phones any more, they're VOIP, but they still use handsets with electrets. Call center style headsets also use electrets.Quote from: coppice on October 15, 2020, 06:31:46 pmYes, I think we established that!Quote from: coppice on October 15, 2020, 06:31:46 pmThat is categorically untrue. Electrets are still omnipresent in pro audio such as broadcast TV. Because of the poor performance and longevity of early electrets, pro audio distanced itself from theword"electret" and just calls them condenser mikes, because electretsarea subtype of condenser mikes. (It simply means a condenser mike that is pre-polarized, as opposed to ones that need external polarization power.) As such, I think it's eminently possible that a significant percentage (perhaps even a majority?) of "condenser" mikes are actually electret condensers. (In pro audio, you'll see reference to "true condenser" to try and signify an externally polarized condenser mike, even though that phrase is technically imprecise since it attempts to mislead one into thinking that electrets aren't truly condenser mikes.)For example, the Sennheiser MKE 2 is a$350lavalier microphone. In a spec sheet, Sennheiser describes it as a "pre-polarized condensor  microphone". And "pre-polarized" is literally the definition of an electret, so it means it's an electret mike in actuality.Again, I don't dispute that the billions of cheap mikes in cellphones and cellphone accessories have largely moved to MEMS, but to claim that the electret is dead is, well, dead wrong.

author: rsjsouza
author_rank: Super Contributor
timestamp: October 15, 2020, 07:13:13 pm
content: Quote from: EEVblog on October 15, 2020, 10:01:41 amThe UJTs are a much more endangered species...2N2646 forever!(I still have a bunch from the ol' days)

author: coppice
author_rank: Super Contributor
timestamp: October 15, 2020, 07:13:35 pm
content: Quote from: tooki on October 15, 2020, 06:59:44 pmHave you been in an office lately? The VOIP phones are mostly ageng. Call centre still need them, but a huge number of desks no longer have a phone on them. Webcams and laptops seems to be using MEMS mics now, and the better ones use multiple mics for beam forming, so they need them to be very small.

author: coppice
author_rank: Super Contributor
timestamp: October 15, 2020, 07:14:13 pm
content: Quote from: rsjsouza on October 15, 2020, 07:13:13 pmI miss the UJT. Its such a fun, flexible device.

author: tooki
author_rank: Super Contributor
timestamp: October 15, 2020, 07:46:41 pm
content: Nice of you to just ignore everything else I said, coppice…Quote from: coppice on October 15, 2020, 07:13:35 pmYes, frequently.Quote from: coppice on October 15, 2020, 07:13:35 pmAnd a huge number still do. In some companies, phones have gone away, but in many, they're still widely used. Industries and companies vary wildly in their communication styles.Quote from: coppice on October 15, 2020, 07:13:35 pmCertainly not universal. I could only find three webcam models that use them. On the other hand, even high-end webcams (like my Logitech Brio 4K) use electrets.Quote from: coppice on October 15, 2020, 07:13:35 pmI saw that in a live streaming camera (which connects to a phone, not a computer), but not webcams. Would make sense though!Again, not saying that MEMS mikes aren't stealing a lot of sales volume from electrets. Just that electrets are FAR from obsolete, at least right now.

author: Benta
author_rank: Super Contributor
timestamp: October 15, 2020, 08:17:38 pm
content: Quote from: EEVblog on October 15, 2020, 10:01:41 amNot a bad idea. Just printing the JFET symbol on a T-Shirt would make 99.999999% of the population wonder what it's about.I love it!

author: Cerebus
author_rank: Super Contributor
timestamp: October 15, 2020, 08:55:12 pm
content: Quote from: EEVblog on October 15, 2020, 10:01:41 amThe JFET Preservation Society.Even got a ready made Society song, just mash-up "The Self Preservation Society" from The Italian Job.

author: bsfeechannel
author_rank: Super Contributor
timestamp: October 15, 2020, 10:03:17 pm
content: Quote from: rsjsouza on October 15, 2020, 07:13:13 pmYou're rich!Digi-Key sell them for almost6 bucks a pop.

author: tszaboo
author_rank: Super Contributor
timestamp: October 15, 2020, 10:06:16 pm
content: Quote from: tooki on October 15, 2020, 06:59:44 pmI was under the impression, that condenser mikes are the ones, that have no built in circuits. Just a metallized sheet hanged in a frame. While electrets have a small metal tube, one end open, and typically they have a JFET or other transistor built in. Electret is actually the name of the material that is used as the dielectric, and for condenser microphones the dielectric is air. So they need more voltage.

author: coppice
author_rank: Super Contributor
timestamp: October 15, 2020, 10:30:13 pm
content: Quote from: NANDBlog on October 15, 2020, 10:06:16 pmCondenser mics, electret or otherwise, are impractical without some electronics close to the sensor. The impedance of a condenser mic is very high, so as soon as you pass its signal through some mic cable it would be heavily low pass filtered by the capacitance of the cable. Therefore you need electronics to bring down the impedance. The usual solution is based on a JFET.Condenser mics usually consist of a rigid metal plate close to a thin plastic sheet coated in a thin metal film. This structure is chosen to be as light and flexible as possible. Sound waves vibrate the plastic sheet. There needs to be a polarising voltage between the two plates, which the sound wave can modulate. This is produced either by an external high voltage, or by using a plastic film consisting of highly polar molecules, which is produced in a strong electric field. This film is an electret, and has a permanent high voltage across the film. This removes the need for an external polarising voltage.

author: tooki
author_rank: Super Contributor
timestamp: October 15, 2020, 11:04:39 pm
content: Quote from: NANDBlog on October 15, 2020, 10:06:16 pmcoppice does a great job answering in detail. But the upshot is, no, those construction details aren’t what defines an electret vs non-electret condenser mike.Quote from: tooki on October 15, 2020, 06:59:44 pmIt seems my hunch was right: while reading up on electrets to try and answer NANDblog’s question, I came across a statement from Shure (one of the big names in pro audio mikes) claiming that “probably 95% of the condenser microphones on the market are the electret type”.Another sourcefound during the same trawl says that MEMS overtook electret capsules in sales in 2014, but that most MEMS microphones are also electret-based! “The MEMS microphone designed is largely based on the design of the electret condenser microphone capsule.” (This I did not know.)

author: David Hess
author_rank: Super Contributor
timestamp: October 16, 2020, 01:36:32 am
content: Quote from: NiHaoMike on October 13, 2020, 11:12:56 pmSome high performance switching designs still do that when an IGBT is not fast enough.QuoteIGBTs take advantage of the same thing; have you ever seen a 100 amp IGBT? Where this matters is at high voltages where MOSFET die size becomes huge.

author: eti
author_rank: Super Contributor
timestamp: October 16, 2020, 02:06:11 am
content: Pendant hour is it? These point by point, pick-apart multi-quoting reply posts truly smack of "no no no, no matter what you say, I'm going to pick apart, analyse and refute absolutely everything you've said, wait and see, and I WILL be right!"Being right is hugely overrated, and also a great waste of one's time. It makes me think many people have naff all better to do than "prove" their (supposed) ability to know more than the other man.Lighten up - it's not that important in the overall scheme of life, and will you recall who "won" on a forum conversation, when you're in the final hours of your life?I also sense a disproportionate dose of confirmation bias is present in a lot of these types of threads, and I don't just mean EEVblog, this bullshit is epidemic net-wide from people who can't accept they're not THAT clever all the time, are only human and make mistakes and miscalculations like everyone else.Calm down, get off your chairs and go for a walk.

author: coppice
author_rank: Super Contributor
timestamp: October 16, 2020, 02:46:05 am
content: Quote from: tooki on October 15, 2020, 11:04:39 pmInteresting. The fairly modern mics I've seen schematics for, or seen inside, had pumps to push the 48V phantom power up to a high voltage. Electrets have real benefits. They can create a really big bias voltage. I had a pair of Pioneer electret headphones in the early 70s. Condenser headphones, like the Stax models, could produce wonderful sound, but struggled to reach high volumes, because they didn't want an extreme bias voltage running down the cable. No problem with the Pioneer electret headphones. They would reach pain levels while maintaining high fidelity.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 16, 2020, 03:19:42 am
content: Quote from: David Hess on October 16, 2020, 01:36:32 amIsn't that the realm of SiC and GaN transistors nowadays?QuoteActually have a few of those in an assembly on the bench. Rated for quite a bit more than 100A, I got it instead of something closer to the 50A or so I actually need for my application because it's cheap.

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 16, 2020, 03:31:08 am
content: Indeed, the 2N2646 UJT, being in a metal can is expensive and essentially in the brink of extinction.But the 2N4870/1 in a plastic TO92 package is significantly cheaper.PUTs like the 2N6027/8 are another nifty device, although more closely related to thyristors than transistors.Neither is, or will become, a mainstream device anymore.

author: tooki
author_rank: Super Contributor
timestamp: October 16, 2020, 08:49:41 am
content: Quote from: coppice on October 16, 2020, 02:46:05 amGiven how mature both electret and non-electret microphone technology is today, I think that what ultimately matters is how carefully the capsule (and the device it’s in) has been designed, and that top quality can be achieved with either technology, when low cost isn’t the primary decision driver.

author: tom66
author_rank: Super Contributor
timestamp: October 16, 2020, 09:41:59 am
content: Up until a few years ago discrete BJTs (e.g. MMBT3904) used to be half the price of equivalent NMOS transistors (e.g. 2N7002), useful for small loads. I see now the price has reached parity so it seems that for most applications any cost advantage there is now gone.

author: coppice
author_rank: Super Contributor
timestamp: October 16, 2020, 09:49:03 am
content: Quote from: tom66 on October 16, 2020, 09:41:59 amFrom my experience with small ICs, I assume the cost of packaging a small discrete, like a 2N7002, now greatly exceeds the cost of the silicon itself. So, the cost of the device is only marginally affected by which transistor is inside.

author: tom66
author_rank: Super Contributor
timestamp: October 16, 2020, 10:10:03 am
content: Quote from: coppice on October 16, 2020, 09:49:03 amStill, there was a price difference, 2N7002 being about twice the price of MMBT3904. We are talking about parts with a sub 1-2p BOM cost though.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 16, 2020, 12:40:34 pm
content: Quote from: coppice on October 16, 2020, 09:49:03 amPerhaps the next step is some sort of simple IC designed to take the place of a small transistor, the value add being built in protection against ESD, overcurrent, and overheating? Such a device, if cheap enough, would work nicely for interfacing sensitive logic to the external world.

author: tom66
author_rank: Super Contributor
timestamp: October 16, 2020, 01:00:54 pm
content: Quote from: NiHaoMike on October 16, 2020, 12:40:34 pmSuch ICs already exist. MOSFETs with built in pull down resistors, ESD protection etc., or NPN transistors with base resistors on the same die. Then you have things like load control devices that can switch a high side load with overcurrent and slew rate protection, for instance TI TPS22919. Many of them are sub 20 cents in volume which when you consider placement costs of the passive components required to replicate them is not bad at all.

author: schmitt trigger
author_rank: Super Contributor
timestamp: October 16, 2020, 01:30:18 pm
content: A positive development in the small signal bipolar transistor are the built-in bias resistors.Makes using them a breeze.

author: tszaboo
author_rank: Super Contributor
timestamp: October 16, 2020, 07:13:21 pm
content: Quote from: NiHaoMike on October 16, 2020, 12:40:34 pmWhat you describe is called "load driver", "relay driver", and MOSFET driver, solid state driver, and so on

author: bsfeechannel
author_rank: Super Contributor
timestamp: October 20, 2020, 02:15:46 am
content: Quote from: Benta on October 14, 2020, 10:26:54 pmThe truth is that JFETs have never enjoyed the widespread use that BJTs or MOSFETs have. This is the 1976 transistor catalog of IBRAPE, a subsidiary of Philips.You can see some audio signal-, power-, horizontal output- and radio signal transistors among them. But the only JFET is the venerable BF245. So the "pruning", if it ever existed in fact, started long ago.What is ironic is that the bipolar transistor was discovered when physicists were trying to build the first FET, but failed. The BJT appeared as an enhancement over the original transistor and provided the ideas to finally create the (J)FET. However, despite the fact that JFETs most closely resemble the behavior of a pentode, by that time the BJT was already established as the semiconductor replacement for tubes. A few years later the MOSFET came up and rendered the JFET further irrelevant as a general purpose solution. Had they succeeded in inventing the JFET before the BJT, who knows how different history would be.In all those years what I've seen JFETs do was to work as LF/RF front ends, RF oscillators, switches for analog signals, electronically controlled resistors and constant current sources or sinks. And some obscure or very specialized applications.My hope is that in 20 year's time baking your own JFET, or any other semiconductor, be as inexpensive as producing your own PCB and you will be able to have it done to your specs for 2 bucks.