
Circuit building: stop using antique parts (2014) - 6581
http://sensitiveresearch.com/elec/DoNotTIP/index.html
======
ChuckMcM
Sigh.

I like FETs as much as the next engineer but if you're going to write about
them, try to not make things worse.

In particular, this made me sad: _the 10K resistor to ground isn 't strictly
necessary, but it ensures that the MOSFET remains OFF if the arduino is
disconnected or it's pin is not an OUTPUT._

I was helping a high school student with a transistor project and he was
complaining that "half the FETs he bought were 'bad'". And they weren't really
bad, but they were destroyed. They were destroyed because, like our author,
the student had no understanding of how the FET worked and so didn't realize
that when you exceed the maximum Gate voltage on a FET it generally causes a
current to "jump the gap" to the source and that permanently breaks it. What
is even more, since the gate is essentially a capacitor, you can just touch
the gate with your finger and pass enough charge (without feeling a shock or
anything) to greatly exceed the gate voltage. Pick up the FET without being
grounded and "boom!" dead FET.

Now there is almost no way to generate enough current by touching a Bipolar
transistor to kill it, and so they continue to work for a long time while
plugging them in and out of breadboards.

Do they dissipate more power? Absolutely. Are they difficult to run in
parallel? Sure. But they are pretty robust parts. Sort of like the difference
between alkaline batteries and LiON rechargeable batteries. Sure the latter
are a "better" choice, you can recharge them after all, but if you use them
wrong they catch on fire, if you short an alkaline battery it gets hot but
doesn't go ballistic on you.

So those "antique" parts are generally very cost effective, very robust, and
easy to get. So they make excellent tools to teach you the basics. Do you want
to stay with them as you get more advanced? Probably not, but you're probably
not skiing on the same skis you learned on either.

/endrant

~~~
aexaey
Yep. It is indeed easy to ruin a FET with minuscule amount of static charge.
That is, unless there is a zener (or two, back-to-back) connecting gate to
source. Many modern FETs have this built right in. E.g. ATP214 [1].

[1]
[http://www.onsemi.com/pub/Collateral/ENA1712-D.PDF](http://www.onsemi.com/pub/Collateral/ENA1712-D.PDF)

~~~
Obi_Juan_Kenobi
That does sound like a very useful part for learning purposes, as well as
general robustness, but they don't appear to be particularly common. I get no
results on eBay, nor can I find through-hole packages.

Do you know of anything available like that?

~~~
mrob
NXP makes a version of the popular 2N7002 with ESD protection:
[http://www.nxp.com/documents/data_sheet/2N7002CK.pdf](http://www.nxp.com/documents/data_sheet/2N7002CK.pdf)

Surface mount only (like most modern transistors), but SOT-23 isn't too hard
to hand solder. There are lots of breakout boards for surface mount packages
available for prototyping, or you could even solder some mod wire directly to
each pin and put some hot melt glue on it to keep it in place.

------
PeanutNore
I build a lot of guitar effects, and that community is even worse when it
comes to attachement to obsolete components. The discontinuation of J201 JFETs
(in TO-92 through hole package at least) by Fairchild has caused a lot of
upset. My perspective, not widely shared, is that JFETs in general have been
made obsolete by depletion-mode MOSFETs, at least in audio circuits.

Part of the reason, I think, is that a lot of "designers" of guitar pedals
don't understand the math that determines component values for a particular
transistor in a particular circuit so they don't know how to either select a
modern transistor to replace an obsolete one based on datasheet parameters or
to change the collector / emitter / source / drain / etc resistor values to
work right with a new part.

~~~
busterarm
Guitar d00ds having obscure, nonsensical reasons for things because "mah
tones!"? Say it ain't so.

I mean, nearly every tube head on the market has an essentially pointless
standby/bypass switch because of the mistaken belief that you need to warm up
your tubes for some arbitrary amount of time in a modern amp and keep them
warm.

I forget which manufacturer it was that dropped the switch on one model and
saw sales plummet and got freaked out support calls asking why the switch
wasn't there. Next iteration had the switch back.

~~~
failrate
If I ever made analog audio equipment professionally, I would add an entire
series of switches and dials that weren't wired up to anything.

~~~
jandrese
You could label them like "warmth", "aggressiveness", "heart", and have people
go apeshit trying to figure out the best setting for their song.

~~~
PeanutNore
"Girth"

~~~
failrate
Zest, Ennui, Anticipation

~~~
zimpenfish
Frobulator on iOS has "orbit", "vexity", "doubt".

------
blackguardx
There is nothing wrong with bipolar transistors. They aren't antiquated. FETs
have definitely overtaken them in power applications (for good reason) but it
seems hard to displace them for small signal applications. Small signal FETs
just aren't that plentiful or cheap. There are many instances where a small
signal FET makes sense (level translators, etc) but the cost doesn't justify
its use. Using a 2n2222 and the like is appropriate.

On top of that, BJTs excel in many analog applications. There is a good reason
why many analog IC companies make parts using a BiCMOS process. If you are
doing a discrete analog design (generally for performance reasons) you often
need the performance of BJTs or JFETs.

~~~
Florin_Andrei
The article seems mostly right when it's about interfacing logic circuits with
loads that require even moderate currents. FET is king in this field.

I've a little aquarium and I've noticed how fish always get scared when lights
turn suddenly on or off. So I took an Arduino and wrote a timer app for it,
using PWM to slowly drive the output up over 60 minutes (sunrise), keep it at
max for a few hours, then drive it down slowly over 60 minutes (sunset). I
used a MOS-FET to drive the power LEDs directly from the Arduino. Works
fantastic, and the FET is cold at all times. A 2N3055 would have been pretty
hot most of the time.

I've been playing with electronics for a few decades now, so I can't be
accused of change for the sake of change. The old stuff still works, sure, but
there are new toys which are better in some cases.

~~~
aexaey
There is a purpose-designed Chinese chip exactly for your situation - control
brightness of a LED strip based on PWM input. Compared to a bare MOSFET, this
chip gives you higher efficiency, current-controlled (i.e. flicker-free)
output and ability to drive LEDs directly (without current-limiting
resistors).

PT4115, pretty cheap on ebay and other usual places.

~~~
Florin_Andrei
Well, the LED strip I use is a black box (from an electrical perspective). It
just needs 12V, no external resistors.

So I just hooked it up to 12V via the MOS-FET. The PWM signal from the Arduino
(plugged into the MOS-FET) does the job of changing the apparent brightness.

No need for magic chips in this context.

~~~
pareidolia
Your ledstrip probably also consumes about 15 watts per meter since integrated
current limiting resistors dissipate most of the energy; a black box with the
efficiency of a lightbulb.

------
Animats
If you want to switch power, MOSFETs are the way to go today. Voltage drop is
near zero. Digi-Key has over a thousand MOSFETs in TO-220 packages. Here's one
of the cheapest with a low gate threshold.[1] Probably good enough for most
Arduino on/off applications.

MOSFETs do have some problems. They can draw large gate currents for the first
few nanoseconds of turn-on, which can overload whatever is driving them. The
gate input is very vulnerable to electrostatic discharge during handling.
Device failure tends to be into the ON state.

I just went through a big struggle with MOSFET selection for a special purpose
switching power supply. The big through-hole parts have too much gate
capacitance and need too much drive at turn-on. Only in surface-mount could I
get something that would work.

That's the real problem with antique parts. The new stuff is surface-mount
only.

[1]
[https://www.fairchildsemi.com/datasheets/FQ/FQP4N20L.pdf](https://www.fairchildsemi.com/datasheets/FQ/FQP4N20L.pdf)

~~~
sounds
I would love to see something on digikey or mouser that allowed me to search
for MOSFETs in a way that was less painful.

Let's say you wanted to do a special purpose switching power supply. Digikey
doesn't have a column for gate capacitance (for the mosfet), or Q (for the
inductor). All that manual work to read datasheets is terrible, especially if
your design takes a little while to perfect and some of the components go end-
of-life, so you have to replace them.

I personally like to graph the cost-efficiency curve so I actually have to
tabulate lots of mosfets, inductors, and caps, then simulate them in a
spreadsheet.

I know about the specialized design tools done by each manufacturer that will
recommend parts and do a design for you based on your criteria. I want
something that does a much broader search for parts though.

Maybe I should write one. :)

~~~
TD-Linux
Digikey does have the gate capacitance, just specified in a weird way - gate
charge @ voltage. Most higher power FETs are always specified @ 10V gate, so
it's directly equivalent.

~~~
sounds
Thanks! I wasn't able to figure out if it really was directly equivalent.
(Thanks also to sibling comment pointing out Mouser has the same.)

------
Severian
The irony is that the MOSFET he suggests to use, the NTD4906N, is listed as
obsolete on Digikey.

Which is why I pointed out. A lot of reasons people use antiquated components
is probably because documentation and reference schematics are easy to find
and have probably been refined to be very reliable.

~~~
HeyLaughingBoy
Also what you have on hand. 20 years ago I bought about 100 LM324's for a dirt
cheap price. I drag one out whenever I need a non-precision amp or comparator.

------
AceJohnny2
I've recently gotten back into hobby electronics, trying to revive all that EE
knowledge I haven't used in 15 years, and one thing I sorely lack is knowledge
of common components to use.

Online electronics stores are no help because of the overload of possible
components.

Is there some sort of Cookbook out there I could refer to for up-to-date
examples of common circuits and electronic tasks? I mean, I otherwise totally
would've used a 2N2222 transistor for some tasks, because I wouldn't know
better.

~~~
TD-Linux
A lot of manufacturers have parts designed as drop in replacements for older
parts, sometimes even with similar looking part numbers. Another thing that I
often do is use Digikey's search and check their stock quantity to find out
what's "popular". For example, if I want an op amp, I'll go to that category
on Digikey and then first enter a quantity and sort by price. Then I'll start
adding constraints - for example, for a 324 replacement, I might want it to be
through hole (I nearly always do SMD designs though). From that, I
unsurprisingly find the LM324 (it's still one of the cheapest!). But I also
find the MCP6002, which is lower voltage but has rail to rail inputs and is
designed for a capacitive load - perfect for driving a microcontroller ADC.

The truth though is that it's not like the old parts got any worse, and are
still often the cheapest choice. You have to add additional constraints (I
want lower loss, better performance etc) for something else to be "better".

~~~
PeanutNore
I'm using the MCP6002 to drive the ADC of an ATTiny85 for a guitar pedal that
replicates Game Boy sounds. It's got both rail to rail input and output and it
all works happily on 3.3v.

------
mrob
Mechanical relays are not obsolete. They can have lower resistance and
capacitance than solid state equivalents. A good relay is a very close
approximation to a plain wire when closed. Relays are still commonly used for
RF switching.

~~~
karlkatzke
I use mechanical relays to switch AC power for pumps and similar AC motor
loads using DC signals from Arduinos and similar.

I have very very little experience with electrical engineering (I'm in the
Lego mindset of I plug things in according to things I find online until they
work), but is there something I should be using instead with 120V ~3-5 A
loads?

~~~
guyzero
You could use an opto-coupled triac but honestly for a hobby project a relay
is a lot simpler.

[http://www.electronics-
tutorials.ws/blog/optocoupler.html](http://www.electronics-
tutorials.ws/blog/optocoupler.html)

------
spott
The response referenced by Hackaday: [http://hackaday.com/2015/08/17/you-can-
have-my-tips-when-you...](http://hackaday.com/2015/08/17/you-can-have-my-tips-
when-you-pry-them-from-my-cold-dead-hands/)

------
lpmay
There's not much of substance to this article. The world of electronics is a
bigger place than turning a load full on or full off with a Mosfet. A couple
exercises if you want to see why having some BJT's around is handy: Try to
find a Mosfet that turns on at 0.6 Vgs. Compare the leakage Ids leakage of a
Mosfet to the Ice leakage of a comparable BJT. I also take issue with the idea
that "all that extra stuff" is drawn in the Mosfet symbol for "no reason". The
body diode alone is an important factor to consider EVERY time you use a
Mosfet. When you read schematics every day, you're trained to recognize when
diodes will forward conduct in your circuit and having that drawn in the
Mosfet symbol helps you immediately see problems that would otherwise make it
into your final circuit.

------
coreyp_1
Don't tell me that a LM386 is bad without telling me why and what to replace
it with. If you don't, then you're not actually helping me at all, but rather
it just sounds like you're spreading FUD.

~~~
cr0sh
About the only thing "bad" with the LM386 is how finicky it is with component
selection and layout. It's a great little amp when it works well, but
sometimes it will go dopey on you just looking at it sideways. It actually
works better in a PCB situation (breadboarding is where it can be wonky in
operation - ymmv).

As far as a replacement part? I don't think there are many alternatives there
(at least with the same size, and easy to configure - there are a few stereo
ICs I've seen used for class-D amps, but they weren't as simple to use or as
small).

------
duskwuff
The obsolete part I'd really like to see everyone get away from is the 741
operational amplifier.

The 741 was introduced in the late 1960s. It's completely outclassed by modern
general-purpose op-amps; there is absolutely no reason to still be using it
today.

------
dyselon
Is there a good reference for potential upgrades to old, obsolete-ish parts? I
definitely understand that many of the old logic ICs, transistors, and op-amps
have been displaced by better parts, but I don't always know how to identify
them short of a parametric search on digikey and hoping there's not some sharp
corner I missed. I'd find a lot of value in a page that had some
recommendations for "Are you using <OLD PART> for <PURPOSE>? Consider <NEW
PART>!"

~~~
CamperBob2
Not really, because as so many commenters have pointed out, the choice to use
"antique" parts is more of a value judgement than a violation of natural law.

When in doubt, your best move is probably to see what Horowitz and Hill have
to say. AoE3 has a _lot_ of specific component recommendations.

------
joezydeco
MOSFETs driving motors or large coils without spike protection? Good luck with
that. Have a fire extinguisher handy.

------
retrogradeorbit
There's still plenty of reason to use discontinued components in DIY. And that
reason is the form of the component's package.

This is a problem for me when building high end audio circuits. A lot of the
modern components are only available in surface mount forms. I find this with
matched transistor packages. Like a matched quad. There are modern components,
like AD's MAT14 [1], but if you are building your own circuits and using
through hole components your ONLY choice is discontinued components. They
simply are not made in a through hole package anymore.

At some point I'll be forced to move to surface mount, but at the moment
getting old components is a lot easier. And those old components are as good
as the new ones. Just different packages.

If anyone knows of a modern precision matched quad like the MAT14, but in a
traditional package, please reply with the component!

[1] [http://www.analog.com/media/en/technical-
documentation/data-...](http://www.analog.com/media/en/technical-
documentation/data-sheets/MAT14.pdf)

~~~
pmorici
I disagree. Using a stencil and paste with a cheap toaster oven is easier to
make high quality boards than with PTH and an iron. It's fast and almost
always comes out great.

~~~
retrogradeorbit
"easier". Just pull apart a toaster oven. Reconfigure it. Rewire it. Get some
paste. Make a stencil. You know. Easy peasy. Get the software. Learn how to
use it. Get the stencils printing. Easy. Oh, you've got registration problems.
Come on! Its easy! So much easier than spending one minute ordering a through
hole component.

You see, its not actually "easier". Its "easier" to _you_ because you already
have the equipment and are already doing it. Hey! I already know this! This is
easy!

~~~
Kliment
Hey, I teach SMD soldering to absolute beginners, many of whom have never done
ANY electronics. Within an hour and a half they have a working board with
"advanced" components like QFNs and 0402 passives attached. Nobody goes
without a working board. Only equipment needed is a pair of tweezers, a metal
squeegee for paste deposition and a plain off-the-shelf $10 hotplate. No fancy
anything. It's not a setup you'd use for high-volume production, but who gives
a shit, it's enabling technology for hobbyists to use modern parts. I call it
"surface mount electronics assembly for terrified beginners". If you can make
it to an event I'm teaching at, I'll give you a free class, as you're EXACTLY
the kind of person who would benefit most from seeing that there's a middle
way between relying on increasingly unobtainium components and having to have
a pile of fancy expensive stuff to be able to work at all.

~~~
moron4hire
How do you make the solder paste stencil? How do you make the PCB traces?

~~~
Kliment
You can get PCBs made very cheaply these days (dirtypcbs are an example of how
cheap), and for $20-$30 you can have a sheetful of stencils lasered for you so
this is mostly academic, but:

PCBs: You can make PCBs by toner transfer, phototransfer, or milling, just
like you'd make PCBs for through hole designs, except you don't need the
precision drilling you'd need for through hole parts. The transfer methods
need an etch stage, which you can do at home with fairly safe chemicals these
days, see for instance
[http://quinndunki.com/blondihacks/?p=835](http://quinndunki.com/blondihacks/?p=835)
for a very detailed tutorial. With a bit of care you can do double layer this
way, but if you need lots of layer interconnections it's better to outsource
PCB production. It's WAY easier to make PCBs for surface-mount designs at home
because there is a lot less drilling involved.

Stencils: If you have a laser cutter available, cut them from construction
paper. They'll only work once, but you can make a bunch. If you have one of
those label cutting machines, those work too. If you're etching your PCBs, you
can etch stencils from thin copper sheet, using the same method. Another
excellent material that is already the correct thickness is the wall of an
aluminium beverage can. Toner transfer works well for these and can give
excellent detail. Remember most have a plastic coating on both sides, so file
the outside with the image until you get naked metal (check with a
multimeter), transfer on that and then etch. You can get presensitized sheets
of various metals for phototransfer as well. If you only have a handful of
pads you can also plop bits of solder paste on with a toothpick.

What about breadboards? The most common surface mount packages have breadboard
adapter boards available. If there isn't one for the one you want, etch a
board with a bunch of 2.54mm pitch pads along the edge (no holes, you want the
board vertical so you have lots of breadboard space available). Stick any
decoupling caps and pullup/pulldown resistors straight on the PCB so you don't
clutter your breadboard with them, solder a bunch of header pins sideways, and
there you go. You can put a label for the kind of part it is right into the
copper.

Again, unless you're in a hurry or the board is very simple you probably want
to outsource PCB production. If you do that, get a stencil made as well. If
you can combine a bunch of stencils into one file, they probably won't charge
you any extra for a stencil the size of 5 boards compared to one the size of
one, so with a bit of planning you can get stencils EXTREMELY cheaply. And you
can do tens to hundreds of boards with a single stencil if you take good care
of it.

For alignment between stencil and board, if you're getting both manufactured
for you, place two holes on opposite corners of the PCB that are exactly 3mm
in size, and two identical holes in your stencil. Then you can use normal M3
bolts and nuts to fix them together, and it's super-easy to fine-tune
alignment with the bolts in place but not yet tightened. There are pre-made
stencils you can buy which have a selection of component footprints, so if you
have say a little breakout board with just one difficult component you can
apply paste to that with the stencil and do the others with the toothpick
method or with a syringe dispenser (safety note: NEVER put solder paste in
glass syringes, only use plastic ones).

My point in all this? If you can make through-hole stuff you can make surface-
mount stuff, and probably with less effort.

------
platz
Although I am on board with OP's reccomendation, I think many folks using
arduino are in the milliamp range; they are not driving amps of current. So
the 'constant factor' of obtaining less well known parts from digikey is
significant.

Do you really want to provide any more disincentive for budding hobbyists?

------
kazinator
> _40% of the power is pissed away as heat in the stupid TIP120!!! wtf!_

You can find a BJT about just as antiquated with a lower VCE(sat).

Also, maybe don't run a motor off 5V and then complain that the transistor is
eating too much of that voltage.

------
happycube
The irony here is that the NTD4096N is discontinued/NLA. (There are other
suitable parts in the price range, though.)

------
deepnet
Page author is Tom Jennings, the creator of FIDONet, the BBS network that pre-
saged the internet.

[https://youtu.be/_Cm6EFYktRQ?t=2m32s](https://youtu.be/_Cm6EFYktRQ?t=2m32s)

------
jhpankow
You can have my 2N2222's when you pry them from my cold dead hands.

~~~
kosma
Did you mean "your hot dead hands", heated by all that dissipated power? ;)

~~~
happycube
If it's an application where you can+do use 1k resistors for current limiting,
there's no way they're gonna heat up!

(also, 2n2222's are like $3.49 for 50 on eBay US, via US sellers)

------
bschwindHN
I'm an electronics amateur, got a question here:

I use a PN2222 [1] transistor to switch a 5V supply through an infrared LED
from a microcontroller. It works, but should I be using something
better/smaller/more cost effective/more appropriate for the circuit [2]?

[1] [https://blog.bschwind.com/2016/05/29/sending-infrared-
comman...](https://blog.bschwind.com/2016/05/29/sending-infrared-commands-
from-a-raspberry-pi-without-lirc/images/transistorPackCloseup.jpg)

[2] [https://blog.bschwind.com/2016/05/29/sending-infrared-
comman...](https://blog.bschwind.com/2016/05/29/sending-infrared-commands-
from-a-raspberry-pi-without-lirc/images/breadboardCircuit.jpg)

(the resistor in the photo is 680 ohms)

~~~
TD-Linux
No, in fact in that circuit the PN2222 is the only thing limiting current to
your LED. If you switch that to a MOSFET you'll blow up your LED unless you
add a series resistor. (are you sure you aren't already giving too much
current to your LED?)

------
wyc
I think the author describes my point of view and defuses many of his own
points at the very bottom of the page:

    
    
        also, you are likely making one circuit, not planning
        on mass-producing 1,000,000,000 of whatever it is; who
        cares if you spend a buck where a dime might do? you
        want it to work first time every time, right? this is
        art not technology (eg. industrial capitalism); we
        have different design criteria here.
    

That's exactly right. I'm usually making one circuit, and not mass-producing
them. My inefficiencies will likely be limited in scale to no more than cents
per month on the electricity bill. If I were mass-producing, then of course
I'll reach for the low-power switching FETs.

------
burntrelish1273
IGBTs, although very expensive, are also interesting alternatives to MOSFETs
and relays where large voltages need to be switched where speed isn't
critical.

~~~
burntrelish1273
Here's an example of a very large module for 4.5kV and 1.2kA

[https://www.infineon.com/cms/en/product/power/igbt/igbt-
modu...](https://www.infineon.com/cms/en/product/power/igbt/igbt-module/igbt-
module-4500v-6500v/channel.html?channel=ff80808112ab681d0112ab69f8450396)

------
zw123456
While we are on the topic of using more modern parts, if you are controlling a
motor as shown in the example, why not use an H-Bridge chip ?

~~~
TD-Linux
You might only need to spin the motor in one direction.

~~~
zw123456
Yes, but even so, they also have half bridge chips, all the biasing and
compensation, the correct diodes etc. The point is, a motor controller chip is
more modern way that the old transistor or MOSFET way. unless you are
designing some cheapo thing that will be produced in the millions and have to
scrape every penny out of the design, it is better and easier to simply use a
motor controller chip in my view.

~~~
clarry
Maybe you have a box full of transistors and diodes in the closet, because
they're kinda needed for everything or at least very useful to have around.
You can start building yesterday.

If you want that special bridge chip, you start looking through online stores
and datasheets (what a chore, why do they have to suck so hard?), trying to
find the chip that has the availability, a reasonable price, the right specs
and appropriate package for your use. Then you pay the shipping cost on top of
the component, which might be more than the component itself. Then you wait a
week or two for the thing to arrive. Then you pray it is intact and you can
maybe start building. Hope you ordered the right part and didn't make a
mistake in reading the specs.

------
jamesmp98
I'll keep on using 6502's for fun

------
noonespecial
Why use a 120 in todays modern age? Because that thing you're repairing was
Woz'd to the point that that VCE plays an important part in the circuit's
operation.

Keep your TIPS, you might not necessarily use them for that brand new design
of yours, but you'll probably use them for _something_.

------
amelius
For anyone interested, I can highly recommend the course "Structured
Electronic Design", [1].

[1] [https://ocw.tudelft.nl/courses/structured-electronic-
design/](https://ocw.tudelft.nl/courses/structured-electronic-design/)

------
GregBuchholz
Now if only we can get people to stop antique computer languages from 1972.
(yeah, yeah, I know, special cases. In fact I'm current working on a project
using C on three different microcontrollers).

------
nom
Also: the LM317!

Case in point:
[https://encrypted.google.com/search?q=lm317+hot](https://encrypted.google.com/search?q=lm317+hot)

------
kevin_thibedeau
> relays

Can't be taken seriously if he's going to malign the utility of an entire
class of components.

------
shove
Any similar thoughts on the 2N390X series? (Datasheets are a PITA)

------
sunstone
Vce Sat is closer to .2V (rather than 2v) as I recall.

------
monochromatic
Dark green text on a light green background??

------
anneBarcelona
nah, why wasting all this parts? just the production created a huge pollution
and then it was all for nothing,..no no.

------
basicplus2
that's funny really, because MOSFETs were around in the 70's

~~~
smileysteve
The author addressed exactly this fact. They were rarer and pricier (they're
still pricier)

------
el_isma
The page colors are terrible, but he does make a good point. Bipolars out,
FETs in!

------
lightedman
Good luck building a BFO metal detector using MOSFETs without a ton of
additional useless circuitry.

