1N34A Germanium Diode finally found!!

LOL- thanks for the tip-)

Ah yes, BG Micro, also, Electronics Goldmine, All Electronics, Surplus Sales, and a number of others I don't remember so well. They don't often have what you need, and it is, quite literally, their business to know what the market value of their products is, but they're still worth watching for good deals. After all, when's the last time Digikey or Mouser had a "sale"? :)

Tim

--
Deep Friar: a very philosophical monk. 
Website: http://seventransistorlabs.com 

Might be of interest to others here as well:

Tim

--
Deep Friar: a very philosophical monk. 
Website: http://seventransistorlabs.com 

What do you want it for? A low-barrier schottky is probably better for most uses.

--
John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Hmm, Vf and leakage are about the same, aren't they... tempco might be a bit better for the schottky, it'll still be working around 100C (albeit not so well) whereas the 1N34 will be a bad resistor.

Speaking of resistors, I seem to recall testing point-contact diodes before and seeing a couple of variations. Some (presumably, the oldest and lowest-current types) are good resistors past, you know, 0.2V or so. Others are good diodes up to much higher currents (not as good as, but more like, modern diodes).

Even if you had a diode with Vf ~= 0 and a lot of Rs, as long as Ir isn't too bad, it wouldn't be so bad overall -- since it remains more linear, distortion won't be so bad. SNR will be worse, of course, since the desired signal is accordingly weaker.

And hey, there's always 6AL5. I've pushed them to peak currents over 50mA before just fine, and they have very nearly zero charge (SiC schottky can't compare in capacitance).

Tim

--
Deep Friar: a very philosophical monk. 
Website: http://seventransistorlabs.com

1N34A is a classic for crystal radio sets.

The same? Half a year ago I had a case where I needed to quickly decode a weak RF signal, having only an oscilloscope available. Several small signal Schottky diodes only produced fuzz. Luckily I had hoarded scavenged Ge-Diodes as a kid and mostly carry some to sites. An OA85 wasn't a ton better but still so much that I was able to decipher the signal.

Imagine, a diode in a large glass cylinder that is painted shiny black. Today's kids don't even recognize those as semiconductors.

--
Regards, Joerg 

http://www.analogconsultants.com/

Today's kids don't know the word "semiconductor" :-(

Tim

--
Deep Friar: a very philosophical monk. 
Website: http://seventransistorlabs.com

Any idea why the ge diode worked better?

The 1N34 data sheets are very sparse. None that I've seen have v-i curves, and they spec current of a few mA at ONE VOLT forward.

Being a point contact device, capacitance is low and series resistance is high.

I like the Skyworks SMS7621. 0.25 pF, around 300 mV at 1 mA, and way less series resistance than a 1N34.

--
John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

That's why you have to bring it to them in a different way, like Cypress in this example :-)

--
Regards, Joerg 

http://www.analogconsultants.com/

John, Ben Tongue of Blonder-Tongue fame has written about this... why this diode over that in crystal radios. Different signal levels require a different diode to be optimum. (level and impedance)

Here's one article about diodes in crystal radios.

There are more articles.

This comes from Ben's extensive research about crystal radios, here.

Contains 30 articles on crystal radio design and optimization.

And some of his early life experiences found here.

You will probably find it interesting. Mikek

Probably because of the lower Vf. Also, it has a really low capacitance, usuall less than 1pF at -1V.

For the OA85 the curve starts going like a rocket at 200mV:

A Schottky can't do that. Unfortunately they discontinued it already in the 60's when I was a kid. But I scavenged lots from discardrd TV sets. They used them everywhere, not just for demodulating. I also got some of the smaller ones that replaced it.

And they really do not like heat. Any heat.

That's a nice diode. But probably quite pricey. Can it do 200mV at 100uA like the OA85?

--
Regards, Joerg 

http://www.analogconsultants.com/

The (Ge) 1N270 has a bit lower forward voltage (~0.265V @1mA for at least a few samples I have laying around). Data sheet is similarly sparse. They seem to be still available, perhaps old stock.

In the mid to late '80's I used 1N270's by the bucket load to clamp LM324 and LM329 inputs, to avoid substrate diode injection and phase inversion. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 

It's about 195 mv at 100 ua. Series resistance is a lot less. 1N34 is a resistor above about 1 mA. Want some?

We pay about 35 cents for the 7621. Skyworks has an even lower-barrier part, SMS1546, but it's half a pF.

--
John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 

Nah, thanks. I've got a lot of Ge-Diodes here to last me for the rest of my life, and then some.

The series resistance doesn't matter much in RF detectors, usually.

35c is very tolerable, that's less than 10% of an Anchor Steam OBA.

--
Regards, Joerg 

http://www.analogconsultants.com/

Greegor Inscribed thus:

So is OA79/80/81

--
Best Regards: 
                        Baron.

Point contact diodes are cheating;-)

A *real* crystal radio uses a piece of carborundum and a razor blade...

--
"Design is the reverse of analysis" 
                   (R.D. Middlebrook)

Fred Abse Inscribed thus:

I recall using a piece of coal and a small spring with the end turn snapped off !

--
Best Regards: 
                        Baron.