general diode questions?

[tacobender]

Just wondering what I should be looking for when picking out diodes, I've got a huge lot of vintage diodes I would like to use but I'm not quite sure how to pick out this from that. I'm wondering is it all about voltage or what. I've got several devices to test them with, but most layouts only Call for a specific diode, I'm wondering if this really matters or is voltage the deciding factor, and if there are any other points I should consider. Thanks, Mike.

[antonis]

Voltage is THE factor if you deal with some kind of clipping arangement..
(and for series reverse polarity protection..)

Power is another significant factor but that's true mainly for Power Supply purposes (rectification, shunt reverse polarity protection e.t.c)

Switching time is also a factor but - more or less - it deal's with digital circuits..

Just a VERY general guidance..

[teemuk]

Really falls down to application...

Plain rectifier diodes for the power supply? You probably just care about meeting voltage and power dissipation limits required by the application.

Rectifying with minimal signal losses? (e.g. you're making an envelope follower) Now the forward voltage becomes matter of importance.

Waveshaping/clipping? You probably care about forward voltage and overall transition characteristics between reverse and forward biased states.

etc.

Really, depends a lot on what you are actually doing with those diodes.

[duck_arse]

by "vintage diodes", do you mean all germaniums? if so, sort them into groups based on any colours or numbers or bands you can find on them. then, next time you see a circuit that wants a Ge diode, try one (or a pair) from each group, see what you like/what differences you can hear.

then claim hand-selected vintage mojo.

[tacobender]

by "vintage diodes", do you mean all germaniums? if so, sort them into groups based on any colours or numbers or bands you can find on them. then, next time you see a circuit that wants a Ge diode, try one (or a pair) from each group, see what you like/what differences you can hear.

then claim hand-selected vintage mojo.

...I've got germaniums, strange metal military can shaped ones, all kinds of diodes I dont know what half of them are. So if I wanted to use some for a clipping circuit, would I just look up the standard voltage for the diodes in the layout and then test my stock to see what's comparable?

[antonis]

So if I wanted to use some for a clipping circuit, would I just look up the standard voltage for the diodes in the layout and then test my stock to see what's comparable?

Quite right, although it's rare to see diode forward voltage drop written in layout..
(sometimes it isn't written even the type/code of diode - just a rough discrimination about the kind i.e. Si, Ge, LED e.t.c.)

You'll have to look at respective datasheet and then measure your diodes for matching voltage drop..
(but you can also make rough categorization like 500 - 650mV for Si, 250 - 350mV for Ge, 1.6 - 2V for Red LED, 1.9 - 4v for Green LED, about 2V for Orange LED, 2.2V for Yellow LED e.t.c.)

[duck_arse]

if you could herd all your stash into one field of view, and take a photo, we're always happy to take a lookkk.

[Guitar Poppa]

Just wondering what I should be looking for when picking out diodes

Hello,

>>> As Duck_arse wrote the first parameter is "germanium or silicium ?"...
The output level depends on this alternative, as well if the diodes are used in a feedback loop or as load... With germanium, the level will be a bit under 200mV and it will be a bit over 600mV with silicium. If you want more level with germanium, just place 2 or 3 diodes in series...

There is another consequence : Using Ge or Si will change the sound texture : The saturation of silicon is more contrasted, the germanium is softer and seems to produce something more like a compression than a clipping, especially when the diodes are used in a feedback loop.

>>> In each family, Ge or Si, there are slight differences in sound depending on the model used. Slight but sometimes hearable. The factor is the form of the saturation curve, and thus the dynamic and harmonic behavior of each type of diode. For example, I noticed more fat and lower medium with 1N4448 than with the conventional 1N4148... With germanium, it can be interesting to compare the old European OAxxx with the AAxxx who succeeded them. Thame thing between different american 1Nxxx...

As Teemuk wrote, it is best to try on classic circuits : a Tube Screemer type with diodes in the feedback loop, and a Rat type with diodes loading the OpAmp...
No encrypted parameters, no datasheet won't never predict that your ear detects ; not even an oscilloscope. This is why DIYers and craftsmen can do better than the industry ! Just take the time to realize your experimental circuit, take your instrument, play and write down all your impressions ... Come back a few days later and compare your impressions.

Happy to give a hand...
Guitar Poppa