Favourite parts with off-label uses?

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Following up on blocher's sterling work,(*)

Many of us use parts off-label, often very successfully. A few examples:

SAV-551+ pHEMTs make very good wideband bootstraps. Their f_max is around 12 GHz, but they're amazingly stable.  

74HC4352s make good flying-capacitor diff amp front ends.

TMUX1511s make very nice analogue lock-ins--their Coff*Ron FOM is almost in a class with relays, but 1E5 times faster.  

Zero-ohm jumpers have about the right resistance to stabilize LDO regulators with ceramic output caps. (It's good to be able to disconnect the supplies during bring-up, and putting the jumper between the reg and the output cap has this additional benefit.  

Your faves?

Cheers  

Phil Hobbs  
(*) who may be bulegoge's good twin, given the similarity of their emails ;)

--  
Dr Philip C D Hobbs  
Principal Consultant  
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Re: Favourite parts with off-label uses?
On 4/4/2020 8:49 PM, snipped-for-privacy@gmail.com wrote:
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The TL431 can be used as a multiple-feedback filter real easy  
particularly with a 5 volt supply; the 2.5 volt reference is the  
"virtual ground" and you only need the inverting input. keeping in mind  
its adjust pin draws more current, 10s of microamps, than the average  
bipolar op amp.

Common-anode 7 segment red LED display and 5 volt supply just use a  
TL431 connected two-terminal between the display anode and supply and  
drive the segments to ground with a uP, constant voltage and no  
current-limiting resistors needed. Seems to be just about the right  
brightness and very temperature stable with every red 7 segment I've tried.

kind of like toilet paper, duct tape, and WD-40 as a lubricant, the  
TL431 is good at many tasks except the one it says on the label.

The LM386 is good for driving small brushed DC motors and the DIP  
package can dissipate a lot of power and is very rugged. (thought I  
guess that's technically in the data sheet but not really elaborated on)

Re: Favourite parts with off-label uses?
On Saturday, April 4, 2020 at 8:49:22 PM UTC-4, snipped-for-privacy@gmail.com wrote:
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 12 GHz, but they're amazingly stable.  
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in a class with relays, but 1E5 times faster.  
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ors with ceramic output caps. (It's good to be able to disconnect the suppl
ies during bring-up, and putting the jumper between the reg and the output  
cap has this additional benefit.  
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The Skyworks SKY66318-11 (3300-3600 MHz instantaneous bandwidth, high-effic
iency, linearized RF power amplifier) makes a pretty good fuse.




Re: Favourite parts with off-label uses?
On Saturday, April 4, 2020 at 10:43:46 PM UTC-4, mpm wrote:
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:
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nd 12 GHz, but they're amazingly stable.  
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t in a class with relays, but 1E5 times faster.  
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ators with ceramic output caps. (It's good to be able to disconnect the sup
plies during bring-up, and putting the jumper between the reg and the outpu
t cap has this additional benefit.  
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iciency, linearized RF power amplifier) makes a pretty good fuse.

What exactly are you trying to protect, a Littelfuse Polysorb?  

--  

  Rick C.

  - Get 1,000 miles of free Supercharging
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Re: Favourite parts with off-label uses?
On 2020-04-04 22:43, mpm wrote:
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I feel your pain. ;)

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Favourite parts with off-label uses?
On Sat, 4 Apr 2020 17:49:18 -0700 (PDT), snipped-for-privacy@gmail.com wrote:

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They make excellent switches too. Rds-on is never specified for RF
parts, but it's about 2 ohms for the 551.

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Some digital bus and USB switches are cheap and are excellent,
super-fast analog multiplexers.

Some chips are useful just for their ESD diodes.

LVDS line receivers are super-fast, dirt cheap RRIO comparators.

An LED can be used as the voltage reference for an NPN current source.
The tempcos can be made to almost cancel.

High value AlN resistors can be used as thermal bridges.

Surface-mount platinum RTDs can be used in experiments, as both heater
and sensor, to quantify resistor heat sinking and thermal transients.

Surface-mount resistors can be last-resort fuses.

Low-barrier schottky diodes can be used in reverse as constant-current
things. Tempcos are not great. The same diode can charge and discharge
a capacitor.

Some self-protecting SSRs can be used as electronic fuses. As can a 3t
regulator with the adj pin open.

Depletion fets are nice capacitor bleeders. Ditto 3t reg as a current
sink.

A bit of open-load transmission line can be a high-frequency peaker. I
have that option in my GHz o/e layout.

Someone said never use an opamp as a comparator. They were wrong.

An rro opamp can also be used as a current limiter/fuse.

You can do all sorts of things with ribbon cable.

Some HV diodes and the c-b junctions of some transistors make awesome
drift step-recovery (Grehkov) diodes.

BFT25s can be used as fA-leakage diodes.

Dual-winding inductors, like DRQ127, can do all kinds of tricks.

Microwave MMICS can be fabulous pulse amplifiers.

Zeners are good noise generators.

3t regulators can be good power amplifiers

Phemts can make amazing diodes. Too bad they are mostly gone.

Inside an FPGA, a dual-port sram can make an otherwise impossible
giant crossbar switch.

LVDS inputs on an FPGA make OK comparators.

Violating setup/hold specs on fast flipflops can be interesting.

Gates are delay lines.

One dual optocoupler can make a great high voltage amplifier output
stage. No level shifting problems.

PV optocouplers can be used as floating power supplies.

Unshielded drum-core inductors can be mag field sensors or
high-voltage signal/power isolators.

A toroidal inductor can be a liquid level sensor.

Trimpots can be decoded as 2, 3, maybe even 4 position switches. Or
use a high resistance pot as an SPDT on-off-on switch.

Why are there no surface-mount fans?





--  

John Larkin         Highland Technology, Inc

Science teaches us to doubt.

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Re: Favourite parts with off-label uses?
On 2020-04-05 00:09, snipped-for-privacy@highlandsniptechnology.com wrote:
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I've used them like that at your suggestion.  Snazzy if you don't need
super low offset voltage.  (And if you do, every comparator slows way down.)

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That's interesting.  I recall discussing some very expensive parts sold
specifically for DC isolating thermal pours.

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Interesting.  Are they reasonably repeatable unit-to-unit?

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Interesting.  How does that work?  Normally I think of O/C tlines as a
series resonance to ground.


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Gotta watch for the antiparallel diodes on the inputs, though.  For slow
stuff, LM358s work great as comparators--the inputs survive going way
above the supply.

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Annoying that they don't tell you k in the datasheet, and you can't even
back it out from the series-connected inductance, which is quoted as
exactly four times the parallel-connected value.
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Well, MCL is pretty good about keeping stuff in production.

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How so?

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Poorly specified ones, though--at least in 74HC, typical propagation
delay specs are half of the maximum.    Of course, my usual rule for
one-shots is to avoid them unless the circuit would be okay over a 3:1
range of delays.

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That one I haven't heard about.  Are you looking for the NMR signal? ;)

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BTW, did you find a good replacement for that discontinued Murata PV2A
one that works up to 1-2 GHz?

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Dunno, but maybe because high temperature engineering plastic is
expensive.  You could probably make them with graphite block bearings.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Favourite parts with off-label uses?
On Sun, 5 Apr 2020 10:52:29 -0400, Phil Hobbs

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For modest values of reasonable. It's Is, which is huge for
schottkies, hundred nA sorts of numbers. I've posted my RF detector
which is a diode and a capacitor. It's in production.

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Stick a drooling-rise step into one end of a transmission line and it
will overshoot and snap up the waveform at the other end. Adjust the
source impedance, or terminate a little, to trim the step response.
It's sharper than RC peaking, so compensates things like Ft rolloff or
skin effect.

I had a profound, life-changing revelation recently. If you don't poke
a fast rise into a passive transmission line, you won't get a fast
reflection. I wasted all those years designing absorptive lowpass
filters.

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The k's are really high. Easy to measure.

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Yes, but they are little ones. The Avago SOT89s were great 1 amp, 1
pF, zero recovery diodes.

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We are measuring timings and jitter to fs resolution by sweeping one
edge across another, clock and D on a GigaComm flipflop, and averaging
the Q output. I have some data if anyone's interested.

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That's often all you need, some sort of glitch.

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A conductive liquid is a shorted turn.

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Don't think so. I'll check. Production hates them... hard to adjust.

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We're putting fans on PCBs with angle brackets. A fan blowing directly
on parts is wonderful thermally. Almost like they designed them to do
that.

They could also put tapped holes at 90 degrees.

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--  

John Larkin         Highland Technology, Inc

Science teaches us to doubt.

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Re: Favourite parts with off-label uses?
On 2020-04-05 11:42, snipped-for-privacy@highlandsniptechnology.com wrote:
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Okay, so not really open-circuited.  I'll try it out.  That could  
potentially have helped that single-diode sampler gizmo--its speed was  
limited by the rise time of the line receiver driving the pHEMT switch.  
That one used a capacitor plus a short, mismatched shunt stub to make  
the sampling pulse from a falling edge.

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Gasp! ;)

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That's unusual for a 'coupled inductor'.  I normally expect it to be  
around 0.85.

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Ah, okay.


Right, I saved the schematic from when you posted it awhile back (2014).  
  That was a 10EP52, which is now available only from Rochester.  I'd be  
interested in the data and the updated version, sure.    I'm sure I'll  
need to do that one of these days.

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At sufficiently low frequency, anyway.

We've started putting little Sensirion T/H sensors in a lot of things.  
When using TECs, it's awfully nice to be able to compute the dew point,  
for instance, and in outdoor applications (e.g. our fire sensors for  
harvesters) it's good to be able to predict when the window is liable to  
fog up on the inside.

We use IP67+ enclosures with bags of 5A molecular sieve inside, which is  
super cheap and will absorb 50% of its own mass in water.  Simon has had  
to learn a whole lot about enclosures and mechanical design generally.  
Turns out that you have to put an air vent on the enclosure to prevent  
pumping water inside due to atmospheric pressure differences.  That  
leads to working of the O-ring seals, which wears them out.

We considered using a bellows, but atmospheric pressure varies +-7% or  
so, which makes for a pretty big, floppy bellows.  Hermetic construction  
is possible but very expensive, and relies on glass or ceramic insulated  
connectors.  The glass would have had to be brazed or indium-soldered to  
the lid, which leads to CTE mismatch problems.

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Yup.  Hard to replace for times you need them, though, e.g. gain peaking  
tweaks.  You aren't doing that with a dpot.
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Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Favourite parts with off-label uses?
On Sun, 5 Apr 2020 12:17:03 -0400, Phil Hobbs

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The soft peaking helps when a step has a soft corner on the rise,
which is very common. That's why people who do fast stuff cheat and
measure risetime 20/80.

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The DRQs are bifilar. Two or three 9's.

And a lot of capacitance. They make nice autotransformer flybacks.
Does that have a better name?



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A balloon inside?



--  

John Larkin         Highland Technology, Inc

Science teaches us to doubt.

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Re: Favourite parts with off-label uses?
On 2020-04-05 13:39, snipped-for-privacy@highlandsniptechnology.com wrote:
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Doesn't help--you need something to reduce the pressure drop across the  
seals.  An aluminized rubber diaphragm  inside the box, with one side  
vented, might work.

I made a calculation that 50 grams of 5A molecular sieve would keep the  
inside dry for about 10 years.

The board has a T/H sensor on it, so it can complain if the sieve gets  
saturated.

We're conformal-coating the boards, and the sensors are running at zero  
bias.  Doing the latter is unusual for me, but the bandwidth only needs  
to be 200 Hz or so.

Cheers

Phil Hobbs


--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Favourite parts with off-label uses?
While not a component...

Early in my career, it was demonstrated to me that you could make a reasonably accurate RF millivoltmeter out of an analog Simpson 260 voltmeter.  

(Without modifying it, of course.)

Re: Favourite parts with off-label uses?
wrote:

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Mo found this at some neighborhood junk sale and bought it for me. $3
or something.

https://www.dropbox.com/s/tz0panr4f1nlqer/RF_Ammeter.JPG?raw=1

It's probably a thermocouple.

How did that Simpson thing work?

I have some Spice models of an RF detector using an SMS7621
low-barrier schottly. It works around 50 mV RMS.



--  

John Larkin         Highland Technology, Inc

Science teaches us to doubt.

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Re: Favourite parts with off-label uses?
On Monday, April 6, 2020 at 9:43:33 PM UTC-4, jla...@highlandsniptechnology
.com wrote:
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onably accurate RF millivoltmeter out of an analog Simpson 260 voltmeter.  
  
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   Yes, they are Thermocouple meters. Those were used to measure the curren
t to an antenna.  

   Larger ones were used in Broadcasting to log transmitter output in the s
tation's daily engineering logs for the FCC.


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   Simple RF probes. There are a lot of minor variations. I have a Fluke85R
F. The link is for a two page manual, and schematic. It used a Germanium di
ode, but modern diodes are usable. and have a better frequency response. Th
e ARRL handbook has had a probe design in every issue that I've ever seen.  
The early ones used a dual diode tube like a 6AL5.

If you need better accuarcy at low levels, an old Boonton 92 series is hard
 to beat. Its sucessor, the 9200 is even better. It is digital and it has I
EEE-488 interface as an option. Probes often cost more than the meters, and
 the cables are as well, but you can find them on Ebay. I've ought 'unteste
d' 92 meters with a probe and cable cheap, because the seller is clueless.  
I will be building clones of some of their probes, now that I have a lathe.
 and suitable shielded cable. Wirepro still makes the origin Amphenol two p
in microphone connectors, and I have a new, 250 foot spool of the cable.

<https://www.schematicsunlimited.com/f/fluke/fluke-85rf

Re: Favourite parts with off-label uses?
On Monday, April 6, 2020 at 9:43:33 PM UTC-4, jla...@highlandsniptechnology
.com wrote:
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onably accurate RF millivoltmeter out of an analog Simpson 260 voltmeter.  
  
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Wow John, that is a nice looking vintage analog meter!!
Nice find.

From an old, faded, memory...
The trick with the Simpson 260 was you connect the red lead to the uAmp inp
ut, and put the black lead in the Common (-).  But, you don't connect the b
lack lead to your circuit.  What you do instead is loosely drape is across  
the unit under test, and then probe with just the red lead.   Essentially,  
the meter is reading rectified RF.

The above description about just leaving one lead disconnected but loosely  
coiled-up in close proximity to the circuit under test is correct.  But I m
ight have the meter connections wrong.  At this point, I would probably hav
e to have a Simpson 260 in front of me to figure it out -- but it's basical
ly along those lines.   The meter's not designed to do it, but it will.   A
nd it more accurate than you would think, for such a weird, oddball approac
h.  But hey, if you need a relative RF millivoltmeter and don't have one ha
ndy.....   :)

You can also fix a Quintron QBT-250 paging transmitter with a 9-iron golf c
lub, and certain old Ford pickup trucks with garlic bread.  (Maybe I shared
 those stories here before?, but they're a little off-topic in any case.)  
:)

You got a use in mind for that meter?  (Just wondering)

Re: Favourite parts with off-label uses?
wrote:

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The old VOMs used copper oxide rectifiers! Before silicon was
discovered.

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It's a sin to waste garlic bread.

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No, it's just on a shelf for admiration.


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: Favourite parts with off-label uses?
On Mon, 6 Apr 2020 17:43:46 -0400, Phil Hobbs

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I meant that it would be vented to the outside. Little plastic tube or
something.


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I guess the seive would soak up humidity and reduce the pressure
inside, so a tiny flow through the seals would introduce a little more
humidity. Wouldn't that eventually get to zero humidity and zero
pressure differential?

I guess atmospheric changes would still pump the system slightly.

Mothballs?


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--  

John Larkin         Highland Technology, Inc

Science teaches us to doubt.

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Re: Favourite parts with off-label uses?
On 2020-04-06 21:35, snipped-for-privacy@highlandsniptechnology.com wrote:
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If we start with a dry atmosphere inside, humidity by itself would not  
be a first-order forcing function.

Air pressure varies +- 7% or thereabouts on time scales of a few days.  
If you assume that the variations are the same inside the box, you can  
calculate how much water will get in.

Our stuff has to work in medium-extreme conditions.  Harvesters are  
still working in January in some places--I've spent a little January  
time in West Texas installing and verifying installations, at  
temperatures well below freezing and with high winds.  Simon has done  
about three times more of that stuff.  It's difficult.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Favourite parts with off-label uses?
On 2020-04-06 21:35, snipped-for-privacy@highlandsniptechnology.com wrote:
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Vented might be okay.  Trouble is, the gas diffusion rate in elastomers  
is many orders of magnitude higher than in metal or glass, so it would  
need to be metallized.  The metal film would have a lot of cracks, of  
course (*), but most of the surface would still be metal.

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Simon's the seal expert at this point.  A sufficiently stiff box, with  
enough screws holding the lid on, and hermetic connectors, ought to be  
able to stay sealed pretty well.  The pressure changes are nontrivial  
though--our box is about 3 x 5 inches, so a 7% pressure change amounts  
to about 15 pounds over the surface of the lid.  They're also fairly  
slow, so it doesn't take much of a leak rate to equalize the pressure.

We're using a cable gland rather than a hermetic connector, primarily  
for cost reasons.  I suspect that enough air will flow inside the cable  
to manage the vent job, but we'll probably have to measure that to find out.

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;)  If we get critters in there, we'll certainly have other problems first.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Favourite parts with off-label uses?
On Tue, 7 Apr 2020 07:55:27 -0400, Phil Hobbs

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[snip]
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A traditional alternative is a long thin tube whose volume is
sufficient to ensure that no inside air gets out or outside air gets
in, despite the +/- 7% variation in ambient air pressure.  Invented by
Louis Pasteur in 1859.

.<https://en.wikipedia.org/wiki/Swan_neck_flask


Joe Gwinn

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