1N34A Germanium Diode finally found!!

People still make Ge back diodes, as rf detectors. They are, I think, the only planar "ic" type fabrication done in germanium, except photodiodes maybe.

They conduct better in the reverse direction than forward, hence the name.

I would have suggested Polypaks.

Now _there's_ a blast from the past. I remember when Digikey was Poly Paks' main competitor, and Jameco was the gold standard. ;)

Cheers

Phil Hobbs

Making an AM detector that has both good linearity and a reasonable dynamic range is one of those deceptively hard problems.

I tend to do one of two things: one or more DLVAs (e.g. SA614s) with some auxiliary calibrator, such as a crystal ringing down, or a PLL with fairly careful offset nulling.

Ring-down calibration is convenient, because your average 80 MHz crystal rings down at something like 1 dB/ms or a bit less. You can anchor the high-amplitude end with linear measurements, and rely on the exponential falloff for the lower-amplitude range.

Cheers

Phil Hobbs

Does anyone actually use just a diode for AM detection anymore? ...Jim Thompson

I recall Jameco, well "James Electronics" as Digikey's competitor. Been using both of them for at least 35 years. My first job out of college was right across the street from James Electronics in San Carlos. Now I do will call if I need something fast.

There were some other surplus companies that were Polypak's competition. A company in Florida called Knapp Electronics that printed their catalog on newsprint.

the > gold standard. ;) Electronics surplus was a blast back then. There was a Cortland Electronics that advertized in the ad section at the back of many electronic hobby mag azines and had a short catalog of oddball stuff? I remember they got surplu s stock of big old Burroughs Nixie tubes and circuit cards full of huge nak ed reed switches (originally intended for telephone switching?) Each reed w as like 2 1/2 inches long and the sound they made when closed or opened was almost like a musical tuning fork. My Dad taught me how to do high quality soldering when I was 9 or so. I rem ember mounting an old tube TV power transformer in a box to power an elemen tary school science fair project where I recreated Edison's light bulb expe riments by winding various types of iron wire around a large sewing needle to make tiny coils and knowing that vacuum and gas apparatus were out of re ach for me at the time. The large amperage 6.3V tube filament power would m ake the filaments glow and then flare and burn open quite nicely. The highe r voltage taps were stubbed and insulated for safety. It was a nice science fair project actually, kids liked seeing the filaments glow briefly and th en burn open. Good for elementary school. At 12 I was building simple audio oscillators that used two multivibrator c ircuits so they warbled. My favorite used 2 PNP and 2 NPN and by changing t he various timing values the noise could be varied wildly. My Dad wanted a loud noisemaker for the business garage so I hung a power transistor and a big scavanged speaker at the end and the warble would cut through a lot of engine noise. I think I built that when I was like 13 and that loud thing k ept running for a decade at least. After a few years it surprised somebody a bit too much so he put a pot or resistor in series with the speaker to dr op the volume and it kept running for many years. By the time I was 18 I was building projects and buying parts from James El ectronics (later Jameco) and Mouser. When I got into TTL I actually missed drawing traces and pads by hand using Sharpie markers as etch resist and et ching with a bottle of Radio Shack Ferric Chloride. I could do a one off pr etty fast. I'd go over the traces a second time with sharpie intil the shar pie ink was fairly dark to guarantee good resist. When I was in college, a few times I would wake up in the middle of the night with a TTL circuit ide a I just had to commit to paper right away. At least two of them were TTL a nd did get built. The local electronics surplus retailers in Minneapolis had quite a heyday i n the late 1970's as well. Some hobbyist printed up and handed out a map to the best dozen or so at one point. There was lots of really good mil grade stuff surplused off cheap. A few years later a quantity of Teddy Ruxpin motorized eyeballs ended up in the Minneapolis surplus market. They seemed oddly out of place to me, more like the kind of surplus you'd expect in the Santa Clara Valley in Califor nia. Shifty wiggling eyeballs appeared in a few bizarre places for awhile a fter that. They hinted at robotics back then but if you look at the old Ted dy Ruxpin ads on Youtube compare them with Furby of today, Teddy Ruxpin loo ks really sad with a cassette tape shoved in his backside.

The classical one was a piece of galenite (lead sulfide PbS) and a catwhisker, to create the first Schottky diode.

Diodes aren't so bad if you have reasonably quick AGC, and they avoid some of the misbehaviour you can get with things like active peak detectors, e.g. subharmonics and limit cycles. Plus they go a lot faster than most ICs, e.g. 18 GHz back diode detectors.

(I made some at 200 THz a few years back, but their nonlinearity was only a few percent. Diodes like that can produce >200 GHz at their output terminals. I'm hoping to have a chance to revisit that later this year, but we'll see in a week or two--it's hard to get signatures during the summer.)

Cheers

Phil Hobbs

Yes, I think you're right--it was Digikey vs. Jameco and Poly Paks vs. the TV repair shop's dumpster. ;)

Cheers

Phil Hobbs

There's a whole lot of generally pretty good Soviet stuff on eBay these days. I got a career's worth of 15 nF feedthrough caps, small ceramic trimmers, small panel pots, and high-ohm resistors.

And the test equipment bonanza keeps on rolling. There are a lot of dealers now, but even so, top quality boat anchors are going for a very few cents on the dollar.

Cheers

Phil Hobbs

There a company with all kinds of cool stuff called Meshna?? or something like that.

In Europe we had mesa and planar Ge RF transistors. For example, this one was a hot commodity among the "discarded TV set pilfering" crowd because you could often find them hidden as the only transistors in tube sets:

WWII radars used silicon, germanium, and even gaas point-contact diodes. One of the RadLab books casually mentions that "a semiconductor triode should be possible."

One whole volume of the RadLab books is "Crystal Rectifiers." They knew a lot about semiconductor physics in 1940.

There were big TO3 and stud Ge power transistors, and I'm guessing that they were a planar structure. If anybody has one, maybe they could decap it and take pictures.

Germanium Power Devices was, I think, the last maker of Ge diodes and transistors. They are now "GPD" and make photodiodes.

I think someone still makes Ge tunnel diodes.

These guys seem to still build Ge-diodes:

But they state that they get the materials from overseas, so probably fabless.

GPD is a pretty good outfit. They're my preferred IR photodiode supplier--their stuff is good, it costs 1/3 to 1/2 of what Hamamatsu wants for the same thing, and you can get the designer on the phone.

Cheers

Phil Hobbs

Is "Oliver Germanium" still in charge?