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