Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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  #21   Report Post  
Old May 21st 20, 08:16 PM posted to sci.electronics.repair,sci.electronics.design
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Default Vintage transistors and tin whiskers

Phil Hobbs wrote in
:

On 2020-05-21 13:33, John Larkin wrote:
On Sun, 17 May 2020 14:15:31 -0000 (UTC), Cursitor Doom
wrote:

Gentlemen,

I have some old OC171 transistors from an old Eddystone short
wave radio I'm restoring. The problem is I suspect they've
developed whiskers, as the resistance readings from e,c and b to
the screen connection are all far too low (sub 10 ohms). A
colleague has suggested blasting the whiskers by tying the ecb
leads together and zapping them against the screen with a 500nF
cap charged to 500VDC. Now this seems a bit counter- intuitive
to me and I'd have thought higher current lower voltage would
be safer for these delicate germanium devices, but WTF do I
know? Is it feasible to remove the whiskers by this sort of
method or any other?

Thanks,

CD


Does anyone still make ge transistors? I can't think of any use
for them.

The only production ge devices I know of (excepting SiGe) are
back diodes, which I think are the only germanium parts
fabricated using lithography.


Ge makes good photodiodes for some uses. They're very leaky, but
if you make the epi thin enough, they can cover 350-1800 nm, which
otherwise requires expensive stacked-die devices. Garden-variety
ones are more like ordinary InGaAs, i.e. 800-1800 nm, which is
much less interesting.

Cheers

Phil Hobbs


https://iopscience.iop.org/article/1.../JJAPS.14S1.57

  #22   Report Post  
Old May 21st 20, 10:39 PM posted to sci.electronics.repair,sci.electronics.design
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First recorded activity by DIYBanter: Nov 2019
Posts: 11
Default Vintage transistors and tin whiskers

On Thu, 21 May 2020 14:12:43 -0400, Phil Hobbs
wrote:

On 2020-05-21 13:33, John Larkin wrote:
On Sun, 17 May 2020 14:15:31 -0000 (UTC), Cursitor Doom
wrote:

Gentlemen,

I have some old OC171 transistors from an old Eddystone short wave radio
I'm restoring. The problem is I suspect they've developed whiskers, as
the resistance readings from e,c and b to the screen connection are all
far too low (sub 10 ohms). A colleague has suggested blasting the
whiskers by tying the ecb leads together and zapping them against the
screen with a 500nF cap charged to 500VDC. Now this seems a bit counter-
intuitive to me and I'd have thought higher current lower voltage would
be safer for these delicate germanium devices, but WTF do I know?
Is it feasible to remove the whiskers by this sort of method or any other?

Thanks,

CD


Does anyone still make ge transistors? I can't think of any use for
them.

The only production ge devices I know of (excepting SiGe) are back
diodes, which I think are the only germanium parts fabricated using
lithography.


Ge makes good photodiodes for some uses. They're very leaky, but if you
make the epi thin enough, they can cover 350-1800 nm, which otherwise
requires expensive stacked-die devices. Garden-variety ones are more
like ordinary InGaAs, i.e. 800-1800 nm, which is much less interesting.

Cheers

Phil Hobbs


Our FLIR has a germanium lens.

https://www.dropbox.com/s/uda77g9w66...Lens.JPG?raw=1



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

  #23   Report Post  
Old May 21st 20, 11:20 PM posted to sci.electronics.repair,sci.electronics.design
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First recorded activity by DIYBanter: Sep 2006
Posts: 633
Default Vintage transistors and tin whiskers

On 2020-05-21 14:16, wrote:
Phil Hobbs wrote in
:

On 2020-05-21 13:33, John Larkin wrote:
On Sun, 17 May 2020 14:15:31 -0000 (UTC), Cursitor Doom
wrote:

Gentlemen,

I have some old OC171 transistors from an old Eddystone short
wave radio I'm restoring. The problem is I suspect they've
developed whiskers, as the resistance readings from e,c and b to
the screen connection are all far too low (sub 10 ohms). A
colleague has suggested blasting the whiskers by tying the ecb
leads together and zapping them against the screen with a 500nF
cap charged to 500VDC. Now this seems a bit counter- intuitive
to me and I'd have thought higher current lower voltage would
be safer for these delicate germanium devices, but WTF do I
know? Is it feasible to remove the whiskers by this sort of
method or any other?

Thanks,

CD

Does anyone still make ge transistors? I can't think of any use
for them.

The only production ge devices I know of (excepting SiGe) are
back diodes, which I think are the only germanium parts
fabricated using lithography.


Ge makes good photodiodes for some uses. They're very leaky, but
if you make the epi thin enough, they can cover 350-1800 nm, which
otherwise requires expensive stacked-die devices. Garden-variety
ones are more like ordinary InGaAs, i.e. 800-1800 nm, which is
much less interesting.

Cheers

Phil Hobbs


https://iopscience.iop.org/article/1.../JJAPS.14S1.57


That's a thin-film bolometer, similar in general character to the ones
used in modern uncooled microbolometer cameras. Compared with
visible/NIR photodiodes, they're slow and very insensitive, but they
sure do have a wide wavelength range.

20 years ago I built an interesting system called "Footprints" that I've
discussed here a few times over the years. It used an array of 96
carbon-ink pixels screen-printed on a 9-um thick free-standing film of
PVDF (which is basically fluorinated Saran Wrap). The pixels were 3 x 5
mm on a 6-mm pitch, to leave room for the wiring. The readout
multiplexer was a single red display LED per pixel.

Diodes ideally conduct in only one direction. The particular LEDs I
used leaked less than 50 fA between -5V and +0.5V bias. Interfacing
them to an AC-only sensor such as a pyoelectric requires a bit of bias
current, which in my gizmo was supplied by four green display LEDs,
which allowed the processor to adjust the average bias current between 0
and about 5 pA per LED.

The optical system was a moulded Fresnel lens made out of HDPE
(bleach-bottle plastic).

When it was done, it had very competitive sensitivity: noise equivalent
delta-T of just over 0.1 K, not bad for something so minimalistic.

We tried licensing it, but couldn't because the parts cost was too low.

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

  #24   Report Post  
Old May 21st 20, 11:26 PM posted to sci.electronics.repair,sci.electronics.design
external usenet poster
 
First recorded activity by DIYBanter: Sep 2006
Posts: 633
Default Vintage transistors and tin whiskers

On 2020-05-21 16:39, John Larkin wrote:
On Thu, 21 May 2020 14:12:43 -0400, Phil Hobbs
wrote:

On 2020-05-21 13:33, John Larkin wrote:
On Sun, 17 May 2020 14:15:31 -0000 (UTC), Cursitor Doom
wrote:

Gentlemen,

I have some old OC171 transistors from an old Eddystone short wave radio
I'm restoring. The problem is I suspect they've developed whiskers, as
the resistance readings from e,c and b to the screen connection are all
far too low (sub 10 ohms). A colleague has suggested blasting the
whiskers by tying the ecb leads together and zapping them against the
screen with a 500nF cap charged to 500VDC. Now this seems a bit counter-
intuitive to me and I'd have thought higher current lower voltage would
be safer for these delicate germanium devices, but WTF do I know?
Is it feasible to remove the whiskers by this sort of method or any other?

Thanks,

CD

Does anyone still make ge transistors? I can't think of any use for
them.

The only production ge devices I know of (excepting SiGe) are back
diodes, which I think are the only germanium parts fabricated using
lithography.


Ge makes good photodiodes for some uses. They're very leaky, but if you
make the epi thin enough, they can cover 350-1800 nm, which otherwise
requires expensive stacked-die devices. Garden-variety ones are more
like ordinary InGaAs, i.e. 800-1800 nm, which is much less interesting.

Cheers

Phil Hobbs


Our FLIR has a germanium lens.

https://www.dropbox.com/s/uda77g9w66...Lens.JPG?raw=1



Germanium makes really good IR lenses. Besides the built-in filtering
action, it has a refractive index of 4. The optical power of a given
surface is (n-1)/r, where n is the index and r is the radius.

Glass is generally around n = 1.5-1.8, so a Ge lens of a given power has
4-6 times the radius of curvature. Aberrations are much reduced due to
the weaker curvature, so a simpler lens can have better performance.
Also of course the diffraction spot size goes like lambda, so in terms
of the diffraction limit a Ge lens at 10 um is like 100 times easier to
design than a glass lens at 500 nm.

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

  #25   Report Post  
Old May 21st 20, 11:29 PM posted to sci.electronics.repair,sci.electronics.design
external usenet poster
 
First recorded activity by DIYBanter: Sep 2006
Posts: 633
Default Vintage transistors and tin whiskers

On 2020-05-21 17:26, Phil Hobbs wrote:
On 2020-05-21 16:39, John Larkin wrote:
On Thu, 21 May 2020 14:12:43 -0400, Phil Hobbs
wrote:

On 2020-05-21 13:33, John Larkin wrote:
On Sun, 17 May 2020 14:15:31 -0000 (UTC), Cursitor Doom
wrote:

Gentlemen,

I have some old OC171 transistors from an old Eddystone short wave
radio
I'm restoring. The problem is I suspect they've developed whiskers, as
the resistance readings from e,c and b to the screen connection are
all
far too low (sub 10 ohms). A colleague has suggested blasting the
whiskers by tying the ecb leads together and zapping them against the
screen with a 500nF cap charged to 500VDC. Now this seems a bit
counter-
intuitive to me and I'd have thought higher current lower voltage
would
be safer for these delicate germanium devices, but WTF do I know?
Is it feasible to remove the whiskers by this sort of method or any
other?

Thanks,

CD

Does anyone still make ge transistors? I can't think of any use for
them.

The only production ge devices I know of (excepting SiGe) are back
diodes, which I think are the only germanium parts fabricated using
lithography.


Ge makes good photodiodes for some uses.¬* They're very leaky, but if you
make the epi thin enough, they can cover 350-1800 nm, which otherwise
requires expensive stacked-die devices.¬* Garden-variety ones are more
like ordinary InGaAs, i.e. 800-1800 nm, which is much less interesting.

Cheers

Phil Hobbs


Our FLIR has a germanium lens.

https://www.dropbox.com/s/uda77g9w66...Lens.JPG?raw=1



Germanium makes really good IR lenses.¬* Besides the built-in filtering
action, it has a refractive index of 4.¬* The optical power of a given
surface is (n-1)/r, where n is the index and r is the radius.

Glass is generally around n = 1.5-1.8, so a Ge lens of a given power has
4-6 times the radius of curvature.¬* Aberrations are much reduced due to
the weaker curvature, so a simpler lens can have better performance.
Also of course the diffraction spot size goes like lambda, so in terms
of the diffraction limit a Ge lens at 10 um is like 100 times easier to
design than a glass lens at 500 nm.


Oh, and the dispersion of Ge out in the thermal IR is much less than
glass in the visible, so you don't even need to achromatize it. The
tempcos of index and of optical path length are quite large, so you do
need to athermalize in general, something that's rarely required in the
visible.

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



  #26   Report Post  
Old May 21st 20, 11:49 PM posted to sci.electronics.repair,sci.electronics.design
external usenet poster
 
First recorded activity by DIYBanter: Nov 2019
Posts: 11
Default Vintage transistors and tin whiskers

On Thu, 21 May 2020 17:26:09 -0400, Phil Hobbs
wrote:

On 2020-05-21 16:39, John Larkin wrote:
On Thu, 21 May 2020 14:12:43 -0400, Phil Hobbs
wrote:

On 2020-05-21 13:33, John Larkin wrote:
On Sun, 17 May 2020 14:15:31 -0000 (UTC), Cursitor Doom
wrote:

Gentlemen,

I have some old OC171 transistors from an old Eddystone short wave radio
I'm restoring. The problem is I suspect they've developed whiskers, as
the resistance readings from e,c and b to the screen connection are all
far too low (sub 10 ohms). A colleague has suggested blasting the
whiskers by tying the ecb leads together and zapping them against the
screen with a 500nF cap charged to 500VDC. Now this seems a bit counter-
intuitive to me and I'd have thought higher current lower voltage would
be safer for these delicate germanium devices, but WTF do I know?
Is it feasible to remove the whiskers by this sort of method or any other?

Thanks,

CD

Does anyone still make ge transistors? I can't think of any use for
them.

The only production ge devices I know of (excepting SiGe) are back
diodes, which I think are the only germanium parts fabricated using
lithography.


Ge makes good photodiodes for some uses. They're very leaky, but if you
make the epi thin enough, they can cover 350-1800 nm, which otherwise
requires expensive stacked-die devices. Garden-variety ones are more
like ordinary InGaAs, i.e. 800-1800 nm, which is much less interesting.

Cheers

Phil Hobbs


Our FLIR has a germanium lens.

https://www.dropbox.com/s/uda77g9w66...Lens.JPG?raw=1



Germanium makes really good IR lenses. Besides the built-in filtering
action, it has a refractive index of 4. The optical power of a given
surface is (n-1)/r, where n is the index and r is the radius.

Glass is generally around n = 1.5-1.8, so a Ge lens of a given power has
4-6 times the radius of curvature. Aberrations are much reduced due to
the weaker curvature, so a simpler lens can have better performance.
Also of course the diffraction spot size goes like lambda, so in terms
of the diffraction limit a Ge lens at 10 um is like 100 times easier to
design than a glass lens at 500 nm.

Cheers

Phil Hobbs


That lens stays in focus up to the point it touches a part. It will
clearly show the hot spot on an 0603 resistor.

Here's a tiny dual transistor,

https://www.dropbox.com/s/dd072w1z2g..._NPN.jpg?raw=1

obviously two separate chips inside.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com



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