Where can one get parts these days?...

[Phil Hobbs]

Clive Arthur wrote:

On 25/04/2022 14:58, jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Apr 2022 08:02:05 -0700 (PDT), \"neo5...@gmail.com\"
neo5bass@gmail.com> wrote:

I suspect if a real source is around, no one wants to tell, but I am
having a hard time trying to get simple passive components. Melf
resistors, Pulse resistant resistors stuff like that.
Are there any places selling basic components besides E-Bay?

Thanks

Don

Why melfs?

The x-chapters (H+H) have some great data on resistor overload.

MELFs dissipate more for a given footprint and can take a bigger solder
fillet which holds them in place better under high vibration,
particularly when the solder\'s weakened at high temperatures, and if
potted, there\'s more body for the potting to hold.

They\'re also much prettier.

Personally, I find them easier to handle if I have to replace one
because there\'s more to grip, but that\'s a trivial concern.

But they have been noticeably harder to obtain for a few years.

Q. Were MELFs originally made that way because they\'re essentially
leaded parts without the leads?  [It goes full circle - chop open a
leaded dipped ceramic capacitor and you\'ll often find inside a surface
mount part with leads soldered/welded on.]

Yup. At one point some bright outfit was selling MELFs with square end
caps to prevent them from rolling around. Dunno if they\'re still available.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[server]

On Fri, 29 Apr 2022 09:54:56 +0100, Clive Arthur
<clive@nowaytoday.co.uk> wrote:

On 25/04/2022 14:58, jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Apr 2022 08:02:05 -0700 (PDT), \"neo5...@gmail.com\"
neo5bass@gmail.com> wrote:

I suspect if a real source is around, no one wants to tell, but I am having a hard time trying to get simple passive components. Melf resistors, Pulse resistant resistors stuff like that.
Are there any places selling basic components besides E-Bay?

Thanks

Don

Why melfs?

The x-chapters (H+H) have some great data on resistor overload.

MELFs dissipate more for a given footprint and can take a bigger solder
fillet which holds them in place better under high vibration,
particularly when the solder\'s weakened at high temperatures, and if
potted, there\'s more body for the potting to hold.

They\'re also much prettier.

Personally, I find them easier to handle if I have to replace one
because there\'s more to grip, but that\'s a trivial concern.

But they have been noticeably harder to obtain for a few years.

Q. Were MELFs originally made that way because they\'re essentially
leaded parts without the leads? [It goes full circle - chop open a
leaded dipped ceramic capacitor and you\'ll often find inside a surface
mount part with leads soldered/welded on.]

https://i.chzbgr.com/full/6919676928/h2C8459FA/melf



--

Anybody can count to one.

- Robert Widlar

 

[server]

On Fri, 29 Apr 2022 10:17:17 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

Clive Arthur wrote:
On 25/04/2022 14:58, jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Apr 2022 08:02:05 -0700 (PDT), \"neo5...@gmail.com\"
neo5bass@gmail.com> wrote:

I suspect if a real source is around, no one wants to tell, but I am
having a hard time trying to get simple passive components. Melf
resistors, Pulse resistant resistors stuff like that.
Are there any places selling basic components besides E-Bay?

Thanks

Don

Why melfs?

The x-chapters (H+H) have some great data on resistor overload.

MELFs dissipate more for a given footprint and can take a bigger solder
fillet which holds them in place better under high vibration,
particularly when the solder\'s weakened at high temperatures, and if
potted, there\'s more body for the potting to hold.

They\'re also much prettier.

Personally, I find them easier to handle if I have to replace one
because there\'s more to grip, but that\'s a trivial concern.

But they have been noticeably harder to obtain for a few years.

Q. Were MELFs originally made that way because they\'re essentially
leaded parts without the leads?  [It goes full circle - chop open a
leaded dipped ceramic capacitor and you\'ll often find inside a surface
mount part with leads soldered/welded on.]

Yup. At one point some bright outfit was selling MELFs with square end
caps to prevent them from rolling around. Dunno if they\'re still available.

Cheers

Phil Hobbs

There are some diodes like that, thin end plates.

Hard potting compounds sometimes expand as they cure, and cure
non-uniformly. Imagine potting getting under such a melf and
fracturing the skinny pin plating.

https://www.apogeeweb.net/ModelImgs/BigIMG/J/JAN1N5811US.jpg

Potting is bad news in general.



--

Anybody can count to one.

- Robert Widlar

 

[Phil Hobbs]

jlarkin@highlandsniptechnology.com wrote:

On Fri, 29 Apr 2022 10:17:17 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Clive Arthur wrote:
snip
Q. Were MELFs originally made that way because they\'re essentially
leaded parts without the leads?  [It goes full circle - chop open a
leaded dipped ceramic capacitor and you\'ll often find inside a surface
mount part with leads soldered/welded on.]

Yup. At one point some bright outfit was selling MELFs with square end
caps to prevent them from rolling around. Dunno if they\'re still available.


There are some diodes like that, thin end plates.

Hard potting compounds sometimes expand as they cure, and cure
non-uniformly. Imagine potting getting under such a melf and
fracturing the skinny pin plating.

https://www.apogeeweb.net/ModelImgs/BigIMG/J/JAN1N5811US.jpg

Potting is bad news in general.

\"Doctor, Doctor, it hurts when I go like this!\"
\"So don\'t go like that.\"

I don\'t recall seeing compounds that don\'t shrink at least a little.
Having one expand might be pretty ugly. OTOH hard potting compounds can
do things like crushing trimpots and electrolytics, so IIRC the wisdom
is to pot the component side in a thin layer of soft, noncorrosive RTV
before putting the epoxy on it.

I\'ve sometimes used conformal coatings, but never potting.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Clive Arthur]

On 29/04/2022 15:38, jlarkin@highlandsniptechnology.com wrote:

On Fri, 29 Apr 2022 10:17:17 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Clive Arthur wrote:
On 25/04/2022 14:58, jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Apr 2022 08:02:05 -0700 (PDT), \"neo5...@gmail.com\"
neo5bass@gmail.com> wrote:

I suspect if a real source is around, no one wants to tell, but I am
having a hard time trying to get simple passive components. Melf
resistors, Pulse resistant resistors stuff like that.
Are there any places selling basic components besides E-Bay?

Thanks

Don

Why melfs?

The x-chapters (H+H) have some great data on resistor overload.

MELFs dissipate more for a given footprint and can take a bigger solder
fillet which holds them in place better under high vibration,
particularly when the solder\'s weakened at high temperatures, and if
potted, there\'s more body for the potting to hold.

They\'re also much prettier.

Personally, I find them easier to handle if I have to replace one
because there\'s more to grip, but that\'s a trivial concern.

But they have been noticeably harder to obtain for a few years.

Q. Were MELFs originally made that way because they\'re essentially
leaded parts without the leads?  [It goes full circle - chop open a
leaded dipped ceramic capacitor and you\'ll often find inside a surface
mount part with leads soldered/welded on.]

Yup. At one point some bright outfit was selling MELFs with square end
caps to prevent them from rolling around. Dunno if they\'re still available.

Cheers

Phil Hobbs

There are some diodes like that, thin end plates.

Hard potting compounds sometimes expand as they cure, and cure
non-uniformly. Imagine potting getting under such a melf and
fracturing the skinny pin plating.

https://www.apogeeweb.net/ModelImgs/BigIMG/J/JAN1N5811US.jpg

Potting is bad news in general.

It\'s horrible, but necessary in high shock/vibration equipment. We use
RTV, as far as I know everyone does for high temperature high shock.

[Actually, it\'s easier to clean a MELF populated board properly too,
though that\'s a very marginal advantage as there will always be lots of
\'ordinary\' SM parts too.]

--
Cheers
Clive

 

[John Larkin]

On Thu, 28 Apr 2022 20:03:56 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Tuesday, April 26, 2022 at 2:13:58 PM UTC-7, John Larkin wrote:
On Tue, 26 Apr 2022 20:50:58 -0000 (UTC),
DecadentLinux...@decadence.org wrote:

Do you design with melfs? Why?

They were to replicate the design and features of glass encapsulated,
hermetically sealed components like diodes and such.

Why?

The glass package is thermally better than epoxies (or used to be)
and extremely well sealed against contaminants. Classic diode test: run
ten or twenty amps through a 1N4007 until you hear a \'pow\' and see smoke.
Then put it on a curve tracer. It still works normally (underneath the epoxy,
the package was plug-sealed glass). The epoxy is burnt and cracked, though.

Do design with melfs?

--

If a man will begin with certainties, he shall end with doubts,
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon

 

[John Larkin]

On Fri, 29 Apr 2022 17:28:25 +0100, Clive Arthur
<clive@nowaytoday.co.uk> wrote:

On 29/04/2022 15:38, jlarkin@highlandsniptechnology.com wrote:
On Fri, 29 Apr 2022 10:17:17 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

Clive Arthur wrote:
On 25/04/2022 14:58, jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Apr 2022 08:02:05 -0700 (PDT), \"neo5...@gmail.com\"
neo5bass@gmail.com> wrote:

I suspect if a real source is around, no one wants to tell, but I am
having a hard time trying to get simple passive components. Melf
resistors, Pulse resistant resistors stuff like that.
Are there any places selling basic components besides E-Bay?

Thanks

Don

Why melfs?

The x-chapters (H+H) have some great data on resistor overload.

MELFs dissipate more for a given footprint and can take a bigger solder
fillet which holds them in place better under high vibration,
particularly when the solder\'s weakened at high temperatures, and if
potted, there\'s more body for the potting to hold.

They\'re also much prettier.

Personally, I find them easier to handle if I have to replace one
because there\'s more to grip, but that\'s a trivial concern.

But they have been noticeably harder to obtain for a few years.

Q. Were MELFs originally made that way because they\'re essentially
leaded parts without the leads?  [It goes full circle - chop open a
leaded dipped ceramic capacitor and you\'ll often find inside a surface
mount part with leads soldered/welded on.]

Yup. At one point some bright outfit was selling MELFs with square end
caps to prevent them from rolling around. Dunno if they\'re still available.

Cheers

Phil Hobbs

There are some diodes like that, thin end plates.

Hard potting compounds sometimes expand as they cure, and cure
non-uniformly. Imagine potting getting under such a melf and
fracturing the skinny pin plating.

https://www.apogeeweb.net/ModelImgs/BigIMG/J/JAN1N5811US.jpg

Potting is bad news in general.

It\'s horrible, but necessary in high shock/vibration equipment. We use
RTV, as far as I know everyone does for high temperature high shock.

[Actually, it\'s easier to clean a MELF populated board properly too,
though that\'s a very marginal advantage as there will always be lots of
\'ordinary\' SM parts too.]

Melfs might be better for high voltage or pA circuits, because they
probably clean better.

--

If a man will begin with certainties, he shall end with doubts,
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon