Retrofitting germanium transistor circuits can be tricky, especially the ones where they rely on the apparent beta being negative, i.e. the CB leakage being larger than I_C/(true beta).
Cheers
Phil Hobbs
These were relatively late germanium technology (0C171) with a high ft and internal screen, so they didn't need the external neutralising network of the earlier germanium types. That encouraged me to try a direct substitution which only needed some adjustment of the base biasing network.
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General Electric built some crappy AM table radios, using leaky Germaniu m transistors. There were no bias resistors in the design. I figure that th ey had barrels of those unmarked rejects from Military projects. The only t ransistor tat was properly biased was the HV audio output transistor. It ha d over 150VDC on the collector.
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.Hi Pimpom, Yeah no shipping to India. But if anyone in the US wants 'em drop me an email.
I looked through and here's a partial list. (say 1 to 4 of each type) Most of them pulled from some circuit.
2n2905 2n1754 2n303 2n1308 2n1309 2n309 Dec1754 dec1305All metal cans George H.
The 2N2905 is Si not Ge, big sibling of 2N2907.
piglet
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.
John Larkin wrote in news: snipped-for-privacy@4ax.com:
General Electric? Hehehe.. You mean Ge as in Germanium.
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
John Larkin wrote in news: snipped-for-privacy@4ax.com:
Also as a side note to the title of this entire thread...
'Vintage transistors' were NOT 'tin plated' like todays parts are. They were Nickel Cadmium plated. A far superior plating but with carcinogenic dangers that caused Cadmium and Cadmium alloys to be banned. But you can still buy, eat and die from Beryllium parts.
Phil Hobbs wrote in news: snipped-for-privacy@electrooptical.net:
Our FLIR has a germanium lens.
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
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
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
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,
obviously two separate chips inside.
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