EEVblog
HTML-код
- Опубликовано: 26 июн 2024
- Dave tears down the Keithley 617 Electrometer, capable of measuring sub-femtoamp (attoamps!) resolution.
Low Level Measurement Handbook: www.tek.com/sites/tek.com/file...
Forum: www.eevblog.com/forum/blog/eev...
Video on the relay matrix: • EEVblog #38 2of2 - Sei...
EEVblog Main Web Site: www.eevblog.com
The 2nd EEVblog Channel: / eevblog2
Support the EEVblog through Patreon!
/ eevblog
Donate With Bitcoin & Other Crypto Currencies!
www.eevblog.com/crypto-currency/
EEVblog Amazon Store (Dave gets a cut):
astore.amazon.com/eevblogstore-20
T-Shirts: teespring.com/stores/eevblog
💗 Likecoin - Coins for Likes: likecoin.pro/@eevblog/dil9/hcq3 
Наука
![NOSFERATU - Official Teaser Trailer [HD] - Only In Theaters December 25](http://i.ytimg.com/vi/b59rxDB_JRg/mqdefault.jpg)
I've got war stories from my electronics lab technician job (before and during my time at uni), including one about building a 13-decade logarithmic ammeter that started down at 10 fA (calibrated), that added 3 lower decades to an existing 10-decade system. The PhDs did the circuit physics, the EEs did the circuit design, but I had to build and test the prototype, calibrate it, push it through DFM (make it repeatable and stable), then write the build, test and tech manuals for it.
Counting electrons is totally nuts: They never wind up going where you want them to. I had to enclose my lab bench within a Faraday cage. I had to remove the anti-static mats, clean everything with Freon, alcohol and/or acetone to remove residue traces. Special cables, special solder, special flux; nothing was standard. I had to take many of my measurements remotely.
The signal source was a unique and ultra-sensitive "current chamber" radiation detector driven by high voltage (~12kV) that was located 100m away, meaning it was connected using ultra-low-leakage coax. A nightmare to develop and test in the lab. The cable capacitance alone was horrible to deal with.
Precision log amps are strange circuits. We put a matched Darlington pair in the feedback loop of a Burr-Brown instrumentation amplifier. Simple, right? Not when we had to surround it with bias and thermal corrections to maintain sensitivity and log-linearity. Which added circuit load, which meant I had to start my testing and calibration a full decade lower, at 1 fA. Which meant detecting down to 100 aA to ensure we could reliably measure 1 fA so we could repeatably calibrate from 10 fA. Ugh.
Once the prototype was working, I had to build 10 pre-production units for environmental and accelerated lifetime testing, to ensure the calibration held for the required time under all required conditions. Double-ugh.
My main technical contribution was to thermal stability: I replaced the heat sinks and thermal straps with a machined block of copper, to ensure the instrumentation amp and the Darlingtons were kept within a fraction of a degree of each other, so the thermal compensation circuits would always work as intended and the calibration would be stable. (We almost had to go to a temperature-stabilized oven, but that would have created a cascade of problems that could easily have made things worse overall.)
At the last minute they changed both the PCB conformal coating and the potting compound. Not something you want to do around calibrated low-leakage high-impedance circuits (despite the new compounds being better). To avoid complete retesting, I "handled" it by redesigning the heatsink to become a sealed box, keeping the new materials far away from my calibrated log amp.
While it was a ton of fun, it was this project that convinced me to switch my major from EE to CE (computer engineering), though I did keep an emphasis on sensor/signal processing.
Actually, being an embedded/real-time instrumentation software engineer who is also a fully qualified lab tech has proven to be an ideal career choice for me. I can prove to the EEs where and how they screwed up, but I don't have to fix it myself! Bwa-ha-ha-ha!
Awesome story, thanks.
Yes on the thermal chamber potentially making things, moving air (even just convection) causes differentials that can hinder instead of help. Been there done that, lost the hair.
I can't believe the folks at Area 51 let you ramble on about such alien technology! You'd better watch your back.
When I hear engineers talking about the great things they've built I often think people who are able to design such devices would probably think that building analog synthesizers and their ridiculously picky and temperature sensitive exponential converters quite simple in comparison.
Most of the time these kinds of engineers are working on government/industrial/medical projects and wouldn't bother taking the time to work on stuff like musical instruments.
I left out so many details to get the story as short as possible.
A logical question to ask would be: "What kind of radiation detector needs accurate readings through 13 decades?"
Well, that's the range of radiation right next to a nuclear reactor, from complete shutdown (cold storage, or 1 mW) to well beyond full power (meltdown, or 10 GW).
The detector and the portion of the cabling within the containment vessel had to survive testing for LOCA (Loss of Coolant Accident), where the system test requires going from room temperature and atmospheric pressure to a shock of well over 2000 C and 200 atmospheres in about 3 mS (the test is done in about 200 mS). The test is conducted at a facility inside an old WW1 artillery bunker, with all personnel half a mile away.
The detector and cabling also had to cope with radiation doses both from a lifetime of normal use next to an operating nuclear reactor as well as from a LOCA. We simply put one of our systems behind the beamstop for a linear accelerator (which dumps a ton of radiation) for about two years.
And that was just a gamma detector. The neutron detectors (for direct reactor power measurement) were even more awesome: They lived (and worked!) INSIDE the reactor vessel, right next to the core! Hard coax! While I didn't work on reactor power detectors for commercial plants, I did work on one for a research reactor. Developing and testing that was a total blast.
The first Western commercial radiation detectors to measure and identify the radiation release from the Chernobyl disaster were some of "my" detectors at a Swiss nuclear power station! (Some lab detectors at a Finnish university slightly beat us to the punch.) Our detectors were measuring the radiation content of the cooling water entering and leaving the plant, and we detected that the radiation of the water coming in was HIGHER than what was leaving the plant!
So many stories.
Oh my word, I found a Keithley 617 in a skip a year ago! It's in working order and I had no idea it was capable of that kind of range! It will now be treated with even greater respect, I'm glad I rescued it. Cheers Dave.
I made a common-mode joke
but it was filtered
Whaa ha ha ha haaaa hhaaaaa
you seem to be dealing with the rejection well
"Keep your used solder wick" Dangerous business giving engineers more excuse to hoard more 'useful' bits and pieces
Unfortunately true, but when doing soldering/ desoldering things more or less regularly you might end up finding some left over pieces in your junk bin in your Lab? ;-)
I'll keep my reel of solder wick until its used up then recycle it. Heat it up enough to melt it and the copper/tin/lead will separate.
@@simontay4851 If you don't snip it off ever few millimeters, so you end with pieces of a few centimeters, These tinned braided pieces are useful as flat high current battery interconnects, when soldering Li-ion cells.
carefull dave, if you hold it sideways the electrons will fall out and skew your 62,5 electron count
Tilting affects crystals!
ruclips.net/video/zILwgQhjC_Q/видео.html
You do actually have a valid point here. At SUCH low current, external magnetic fields and RF could affect the reading depending on how its positioned.
Wonder if the Earth's magnetic field could mess with it in any way?
Julie Brandon Not that I'm aware of rotational field effects in such things, but would be interesting to test.
But after you have the field fixed (or in a know frequency) it will afect all the circuit ... when you mesure it in a differential way they will nuled each other.... because the metal can make the field homogeneous (at least more) over all the circuit
Really like to see a video explaining guards vs ground.
Yep, will have to think up the best way to demonstrate that and test it first.
Totally agree, please do it! 😊😊
Thats not the correct explanation, is it?
Short answer: Insulators aren't perfect and current leaks through them if a potential difference exists across them. Because normal coax cable maintains the shield at a potential of 0 volts and your signal is not 0 volts, small amounts of current leak through the cable's dielectric from the signal-carrying conductor to the shield. Triaxial cable has a guard shield between the conductor and the grounded shield. This guard is maintained at the same potential as the signal. Because there is no potential difference between the conductor and the guard, no current can flow between them, thus helping to eliminate leakage currents. Guards can also be applied to PCB design since currents leak between PCB traces.
I guess that's not really super-short but it's more nuanced than saying that guards don't have current going through them. They totally do because they'll be leaking some current to ground, etc. but the important thing is that your signal is not the part that leaks.
Guards carry no current.
Not only you would use an atto-ampere scale to measure electrochemical stuff. But also, you use it for CMOS reliability. It allows you to determine if your gate oxide suffered from SILC (stress induced leakage current), RILC (radiation induced leakage currents), soft breakdown, etc. We used to stress CMOS test structures ("large" capacitors or arrays of MOSFETs or even arrays of floating gate MOSFETs), and then we measured the gate current, to determine if damage was induced on the gate dielectric.
Nice video Dave! I noticed misspelling on femto and Coulomb in the video... I can see why your RUclips proposition is so important! The amount of work and time that goes into production with a highly technical topic is huge! I'm not picking, just mentioning. We all got the point and learned something all while being entertained, well done!
Even more crazy that this STATE OF THE ART gear is .... HOW DID THEY CALIBRATE THIS THINGS ?. I mean, there most be something even more presice out there .... mind blowing. Now, you can even breath on this can. The stand offs remind me to RF stuff.
But, if they have something even more precise out there to calibrate this, HOW DID THEY CALIBRATE THE OTHER EVEN MORE PRECISE THING?!?!?!
With turtles... it's always turtles all the way down.
Giant eagles
Ultimately, it comes down to rubbing rocks together in a specific pattern. See 'automatic generation of gauges'.
They've got a guy with a realllly steady hand to calibrate the tuning pots
250,000.. million, ohms. 250,000 megohms. what the fuck is this alien shit
I see a black van outside...
EEVblog I am just starting to get into electronics myself, I can safely say I’ve never seen anything like those resistors, or anything on that front end. I can only imagine how much this thing would’ve cost back in the day.
+EEVblog Black van, does this mean you are closer to your trek to Pine Gap, Australia? Mate?
Yeah, I had to pause and rewatch that part multiple times just to get my head around that. I mean, HOW the hell do you measure such a high resistance and in the 80s too.
Must be made of some sort of semi conductor, not just your regular metal film.
250G ohm is 250000000000 ohms. Does Dave even have any multimeter capable of measuring such high resistance?
At 14:59 the 250gΩ resistor is a lowly 5% tolerance unit. 5% of 250gΩ is 12.5gΩ or 12,500,000,000Ω. Anyone even seen a 1gΩ resistor? Sheesh!
Btw. Do you know where the names "femto" and "atto" come from? They are derived from the danish numbers femten (eng. fifteen) and atten (eng. eighteen).
Didn't know that!
Off topic (sorry): Australia and Denmark have a very close royal relation (and an Opera one). The coming danish Queen Mary was born on Tasmania...
Hi Dave, I love your channel very much. Though I'm an electronics engineer like you, I find a lot of inspiration watching your work.
So was it Ørsted that got that idea for the naming? He did make a scientific dictionary, to invent Danish scientific words.
Hi Dave.
The tag or label "Do not touch the circuit board" is because 74CHxxx ICs are actually CMOS ICs and touching the circuit board could potentially zap them due to electro-static dischrges.
Dear lord he touched it....
Nice reference to Jim Williams from Linear Technology! He was a master. I worked for Linear for 16 years and Analog Device has now purchased us. Great minds. Cheers!
Nice video Dave. In the earlier days of SLR camera light measurement we developed log amps that had to be precise down to some 10 pA for lowest short circuit current of the photo diode. A good reminder of those days.
That's the sort of videos I really enjoy whatching. In fact they could be like 2 hours in my opinion. :)
At this point I want to thank you Dave for your great videos, great explanations paired with humor. Your channel has brought me so much knowledge, keep going on!
-> I can't wait any longer for my training to start next month to get even more into this topics. :)
Thanks, and have fun with the training.
Nude virgins with grey beards. LOL. I knew a couple old ham radio guys who fit that description.
How do you even make a 250 gig resistor? Teflon windings?
I would love to know how they make them...
Yeah I wonder how too. Must be some sort of doped semiconductor.
Simple it's just an insulator that is not really good at it's job.
The same way they manufacture ordinary through hole 1% precision and better resistors.
They can easily change the resistance value of the resistance material they use like fex at ordinary carbon film resistor but to get precision they need to do things a little different and they cant get fex 250 GOhm at a small length.
They cover the outside of a ceramic rod (could also be a tube) with the highest resistance material they have and then tune the resistance by doing a long spiral cut (easily seen on the rsistor) in the material so the signal has a long way to go through the resistance material and thus make a resistor of a very high value. The longer the spiral cut the higher the value and they can fine tune a resistor this way like they do with ordinary 1%, and better through hole resistors that are built in the exact say same way as the 250 GOhm one but much smaller due to smaller value.
So there are not anything special with them but they cost since they are not made in huge amount since they are only used in special circumstances, and that goes especially for the 250 GOhm one which will not be easy to get a hold on.
@@EEVblog do you mean the gray bearded virgins or the resistors?
Thanks for cracking open the test equipment archive. Yeah Keithley.
Attoamps = a bee sneezing on a wire causing a few electrons to move.
literally true: 1atto Ampere equals to about 6 electrons per second! And deformation in the lattice of the conductor can easily move thousands of electrons. Even if the material is not piezoelectric.
@@adamrak7560 Not that insane. You can buy fairly cheap low noise op-amps that operate in that range. I once made an amp for a seismometer, that took input from a pendulum connected to a piezo speaker. Literally I could stomp with one foot on the 3'rd floor and have it register in the basement.
@@Tore_Lund links to this opamps?
Hey dave, love these videos with high tech (and sometimes old) test gear. first the good old Fluke and now this beauty
A video on current guards and very low current measurements would really rock Dave ...its a bit late for me since I have been dealing with pA measurements in photo diodes for the last couple of years now ... but man getting your head around guards, high impedance measurements, and just pcb design and cleaning etc, below 1nA is really a big learning curve ... a fundamentals Friday on this stuff would have been an amazing help for me 3 years ago and hopefully others too !!!
Thanks again Dave.
I had a laboratory professor (The director of laboratory education for the whole school of engineering) who pronounced "femtoamps" as "fememtoamps" (rhymed with pimento)
I never figured out whether this was just his dry sense of humor, or if it was just his quirky way of saying that word, sort of like people that say "masononary" bit instead of "masonry."
This reminded me of the Bob Pease "what's all this femtoamp stuff" article and lab segment on National's video.
My 1st thought as you said "i will take it apart" was "please do not break it" ... This is a amazing piece of kit.
I like how often you add new videos these days!
Thanks, I'm trying, but still think I'm slow, lots of other stuff happening.
EEVblog: Thank you, thank you, thank you for this video. You've explained why my measurements were off. I used the non-nude virgins cable !! (or was it the nude-non-virgins? I forget.) It was as simple as that ! Once I got the right cables, everything measured as expected. Thank you again!
I love the color scheme of that thing, much more character than those clinical modern things
Keithley Brown
Nice to meet you
rutger houtdijk lol!
welcome to the 70's
+1 for guard and grounding for high precision measurements video!
Pretty safe to say I will never have a use for this, but it was fascinating to have a look!
Please do a video on guard grounding and star grounding too!
You misunderstand the purpose of the guard shield in the triaxial cable and connectors. This conducting tube is held at the same potential (voltage) as the inner conductor so that no current will flow away from the inner conductor. Only vacuum is a perfect insulator so any potential difference will cause the current we need to measure to leak through the insulation.
Fantastic. Great educational video. Thank you!
I like your enthusiasm. I'm trying to keep up to you. Whew! I'm nuts over your show. A shout out to the mrs. and Sagan. Peace.
A good SMU only gets you part way there. System Isolation and cables and fixtures all contribute to reducing the noise. The smallest I've ever made (fA) were Kelvin force voltage measure current gate leakages, at those levels the triboelectricity of just moving the cables is enough to swamp the measurement. We used a driven guard triax cable. All in a light tight faraday cage. Wipe down the fixture, as skin oils are a leakage path.
Interesting video Dave!!! Can you do a video on grounding and some basic pcb design guidelines? May be you can show effects of incorrect grounding and such in that video
Very nice vid, thank you Dave! :)
That's the Dave we know and love, ie tech and laughs.
I etch my PCBs and all I think is about how thin and weak those copper foil traces are, and how the old point-to-point can handles so much more.
There was one of these sat on the end of the test bench for a couple of years when I was dragged (kicking and screaming) into the technicians room at my university where I was chained down for a while. I don't remember it ever being used and it was going to be scrapped but was rescued and taken home by one of my (even more nerdy) compatriots back in the mid 90s. Never thought I see one again. It's amazing what survives. Looking at the price they fetch I wish I'd taken it home :O
I should point out that whilst I do have the grey (nearly white) beard now, I didn't then and was not a virgin. This probably disqualifies me from being a true nerd :D
christ dave there is precision and then there is precision. this was amazing
Excellent video.
2:23 should be 1 Ampere = 1 Coulomb/second
I have build several current meters with resolution of 10fA at 200Hz. Major problem was drifts, but I handled it to 170aA per degree Celsius. That was really nice circuit, but development took two years.
If I may correct the correction (2:21):
1 coulomb (not coloumb) is 1 amp.sec, i.e. amp x sec not amp/sec.
96485.333 of these coulombs makes 1Faraday (not farad). Also, femto does not have a p (even a silent one; 1:56).
Is very neat test gear, thank you for sharing.
they had 2 of these at work and were chucking them into a dumpster. I saved their lives. both work well and the readings on each are the same or within 1 LSD of each other. I changed out the 2 pin triax for a 3 pin. I have a few low loss triax probes but they are 3 pins.
Nice strip-down, I am adding one of these to my own lab today :)
Thanks Dave.
I have a University Degree in physics. I saw an electrometer ONCE during my time in education and that was for ONE CLASS when I was in high school.
I use one of these babies all the time for characterizing semiconductor devices, amazing device, never knew it was so old
SI prefixes are not to be separated from the main unit. Its nanoamps, just as it is kilogram or millimeter.
Good instrumentation withstands the tests of time.
"i'll just plug some sharp probes up it's clacker" love engineer speak :D. Also diggin the 70s coffee and cream panel design there
I have to admit I initially thought this video was about audio amplifiers from a brand named Atto.
Nevertheless, it was worth the click, very interesting and informative.
I had an instrument like this but not as solidly built. The friction of a couple ground squirrels banging in my neighbor's yard one day threw off the calibration.
I used this before, we used it to measure the resistance on the straps between the cells of UPSs.
That occasional yawning in videos is EPIC.
wonderful episode. thanks a lot!!
15:38 part number TG-168-8524 (4, not A)
are there any further digits?
The caps in the PSU need to be replaced.
Enjoyed the video. In a former life, we dealt with femto-ammeters to read the current from ion-chamber radiation detectors for measuring reactor power. When operating in a different voltage range, instead of avalanche 'pulses' like a Geiger-Muller tube, get a steady femto-current. We had the preamps close to the detectors near the reactor. Getting those triax connectors on the cables just right, while crawling around the framework was a b****.
But, just so you know it was possible, we did it with TUBES. :)
About 20 years ago I was looking a good use for atto-. I'm .0192 atto-light years tall.
I came up with the attoparsec. If I calculated it correctly, it's about the largest diameter cylinder I can comfortably grasp in one hand - roughly three and a half inches. :)
I love that the 250GOhm resister is 5%
That kind of precision is amazing. Ignoring atto, just measuring fA you'd almost want to suspend the device in freespace. Like you said, fart on the other side of the room and it will show something at those levels. of course even if suspended in freespace the fart routine would still be a problem.
Very nice bit of kit in this video. Interesting to see that the 35 year old technology can measure lower current than your more modern Keithley shown at the start of the video. I would hazard a guess that they do have a modern equivalent. I don't want to know how much something like that would cost but if you need it you pay the price.
One minor issue in the video is at 18:10 when some text appears on screen but it is blocked by a pop-up bit of a schematic appearing at the same time.
Holy shit, my mass spectrometer typically has a 10E-15 amp signal o.o I didn't think it was possible to measure less than -16
Amateur :-P
lol, on an "off the shelf" helium mass spectrometer I don't think it is economical to measure less than -16 amps coming off the electron multiplier. The noise created from gasses desorbing from the test system surfaces are probably 2 or 3 decades higher and can cost as much as the mass spectrometer itself to eliminate.
It is fascinating though to think of a day where semiconductor manufacturing is so advanced that the processes need to be checked with a helium mass spec that is sensitive to 10E-14 atm. cc/sec. There are already there for QC checking MEMS devices so maybe another 10 years of development on the wafer side of things will get us there.
@@CafeBikeGirl In practice I don't think it really is. Many measures would have to be taken to minimize noise from the environment to get any meaningful measurements that low. On a mass spectrometer spewing it's own noise all over the place, it is quite impressive in it's own right.
The transformer is crooked on purpose. We used to build audio equipment, and to avoid interfecence, you have to align the transformer in strange angles some times.
in case anyone's wondering, it's about $500-$1300USD on ebay
You need to change the marking on the rear for the AC voltage, still labelled for 110V..
thanks for the multiple giggles
i was never at that level, but the guys that were must have been living on a different planet. i do remember some of the old test equipment and its great to see it again, (And i do remember some of the circuits that we "tuned for Max smoke" ...................the old epic fail.) thanks for the video.
Shit. I thought an atto amp is some interesting amplifier. That's how alien it is.
At 9:17 it looks like there's a gaping hole where solder should be on the most right lower pin of the chip above the Motorola.
That electrometer is a god dam neat instrument.
sorry Dave, had to flag this as extremely pornographic ;)
I love this stuff..thanks for the memories...I worked with the floating circuits starting in the late 80's. IIRC, my favorite Hi-z input op-amp was part# AD549. The old huge Analog Devices' famous thick--very thick--data books had all kinds of PCB design samples for Guard traces and the like.
OK, my question--a bit trivial....in the timespace between 18:04 and 18:14 I was wondering what the text actually read--it is hidden by a FET electroscope (?) front end graphic. I couldn't quite grab it.
This might sound silly, but since Amps are just C/s, can't we count electrons for longer to increase the precision? C/year has at least seven more digits.
Note the ferrite rings around the standoffs on the outside of the case @20:00 and 26:00. No accident, Keithley knows the drill.. Nice!
Ooh, missed that...
Hello, thank you for the great video again. What is the type of those shields? Are they made of some ferromagnetic materials like soft stell or mu metal? Or simply high conductive meterial like aluminium?
Gah! Your humour kills me.. :-D
Thumbs up to see Dave and Brian Benchoff do an article together on HaD.!!
And here I was thinking my 614 was special... nice example there of Keithley brown.
Back in the early 70's or 60's there was an ad in Scientific American magazine for a low current meter. It boasted "This meter can measure fA" in big bold letters. That was in the days where f**k , even in disguised form, was never in print, and even "sex" had a hard time being mentioned. Bob Cunningham, do you know of this ad?
I've only just noticed Dave still has the screen film protector on his 7510 :P
I would love to see a video on making those super high resistance resistors. Those look really cool.
He probably can't upload it on RUclips. Assembled by nude virgins in full moon, you know...
20:30 - "Do not TAUNT this Keithley 617!"
Keithley kicks ass !! I have a bunch of the old 179A DMM's its still my fave bench meter because its small foot print and accuracy , you can null out the leads, and ease of calibration and maintenance . Did I say their cheap.
2:29 There's that word again. "Heavy." Why are things so heavy in the present? Is there a problem with the Earth's gravitational pull?
Samgab yes!
Cool, your videos always give me nightmares, where a piece of equipment such as that is put down on my bench, and the old professor from college is standing over me, saying "It is broke Mr. Ercisson , FIX IT!!" and there I Sit with absolutely no idea what it is even supposed to do, let alone knowing how to fix it. I usually wake up about the time I plug the unit in and try to turn it on. That said, I do love your videos, my shrink gave me some pills that stop nightmares so I can watch your videos again.
Dave, can you make a video on microcontroller history? What people have used in embedded applications since the early days...
amazing
Biaxial is called coaxial
18:10 little fail with the text & image there :D
Must be making mistakes purposely to push his youtube agenda!/s
Yes pls video on ground and guard point
12:05 LOL love it.
Great device - just got one from ebay with some differences. The Triax was missing - someone took it out, but looks liek he was careful doing it as the screws are back in the case with a hole left. Also the Jfet was replaced by a smaller one and the shielding removed, maybe a keithley repair ? Or a repair attempt. The devices powers on so far, but I now need to replace the triax, got one not the same mounting but should fit and have to rewire, the original has a plug for the hot seide, so I have to find a similar connector dont want to solder it to the chain -- hope I get it back to life and nothing else was broken especially the jfet part is very suspect. The device was sold as working but untested (the seller dont know much about technique as the missing triax would have needed a defective selling not working) - But I saw this and the price was ok for this.
Could it be used to used to measure the "forward leakage" or in other words, the forward current of a silicon diode biased with something around only 50mV?
Ha, I just use the 10MΩ resistance on my multimeters voltage input in the 200mV range to measure low currents.
Sadly it's only reasonable in the 14kV to 50kV range of applications.
That special transistor logo looks like the one on the panasonic caps.
Please make a video on Ground and guard difference and its importance....
On the PCB notes at 21:00 it's mentioning using Freon to clean the board.
What would you use these days, seeing as CFC's are banned?
Would probably be fine using other common refrigerants (e.g. R134a/1,1,1,2-tetrafluoroethane). You would have to be really careful about additives and contaminants however
A great cleaning solvent is Ensolve. It's a bromopropane product with incredibly low surface tension and low boiling point. Its optimized for vapor phase cleaning systems and pretty benign on plastics.
@@hexane360 Very funny that your handle is hexane, as I have cleaned flux off with isohexane
"one attoamp
(1×10-18A) corresponds to just six electrons." Holy crap! Imagine counting individual electrons as they pass by!
The 250G resistor is *not* the "permanent input resistance", don't be silly!
It is part of the input offset current cancellation. Even the superest, duperest, selectest J-FETs have some input current and this can be cancelled out with the circuit around Q311, R348, R332, etc.
Why dont they simply use Mosfet instead to achieve the low leakage? Decent types of small signal Mosfets should be quite common at 80s
Because MOSFETs are shit in the gate leakage department.
Not to mention how shit they are in the matching department. In the 80's even more so.