Questions on identification of used diodes

[Robin777]

Hi I am Robin and I am new to electronics. My dad was involved in electronics while in the Air Force and I alwayse have had an intrest but he died before we came to terms in our relationship where we could discuss this kind of thing. My question is there a way to use old diodes and electronic parts for new projects? And how can you tell what voltage they are and such? I know with resistors they have banding that is different colors and you can determin their values that way but with capicitors and diodes there seems to be no markings to make a determination. Any thaughts other than just buying new ones?

 

[Resqueline]

Life can be a paradox sometimes..
Capacitor types can be identified by their looks, and their capacitance can be measured with appropriate meters.
Diodes can be harder to identify, but many of their spec's can be still be roughly determined with suitable test setups.
Are they all completely unmarked? How about a pic of the items in question? A trained eye could say if it's worth the while to test them.

 

[davenn]

many diodes do have markings on them, 1N4001 etc 1N4148,1N914 etc

I have stripped 1000's of components off cct boards over the last 40 yrs for reuse in other projects. Its an awesome way get stock of general components and also of harder to get items.

cheers
Dave

 

[Neight]

since this is about diodes, what is the difference between zener diodes and any of the others. i know with Ge you get lower forward voltage drop and silicone are sort of the current "common" ones to use, but i recently took apart an old TV to look for some 1n34's for a project i am doing. what i mostly found in the television parts looked like pictures i found of zener diodes (clear case, orange core and black stripe at one end) and they are very small. anyone who could shed some light on this i would appreciate it
thanks

 

[Neight]

also, (i meant to put this in my other post) don't make the same mistake i did. I got out my soldering iron and melted the solder and tried to pull out a diode and broke it with nearly no effort cause it was too hot to hold, and i used some tweezers. get a solder wick or a solder sucker to remove the solder while it is hot and then once it's cool, carefully remove the part from the board. i had to learn the hard way, hope this helps!!

 

[(*steve*)]

There are *many* types of diodes. In general they're all diodes, but are manufactured so that some particular aspect is optimised for.

For example, all diodes will have a maximum inverse voltage. For Zener diodes it is carefully optimised to be at a known value and stable over changes in current as far as possible.

Another example is the inherent capacitance in a diode junction. For many purposes you want it to be as small as possible. In variac diodes it is optimised to be a certain range of values. In high speed switching diodes it is engineered to be as small as possible.

There are also quantum effects in diodes. Some diodes are manufactured to enhance these effects. Tunnel diodes are an example.

And the list goes on...

oh, and most (modern, not light emitting) diodes are made of silicon. Most Hollywood breasts are made of silicone. *big* difference.

There are many packages for diodes. Other than for light sensitive or light emitting variants, the case is not generally indicative. You won't find many rectifier diodes in small glass envelopes. You could tend to think glass = small signal, epoxy - rectifier, but it doesn't apply to surface mount as (aside from MELF packaging) almost everything is in a piece of black epoxy.

 

[shrtrnd]

If you got these parts from your dad, they may have military markings on them.
In any case, you should be able to google the numbers on the diodes (or whatever device)
Then you can either get data sheets on the devices, or look for cross reference if you need to.
Other devices usually have standard marking on them.
You can download capcitor marking tables, diode color band marking tables, resistor color codes (military resistors usually have the actual value stamped on them, usually
the first 3-digits are the value, with the last digit as the multiplier. A 4702, is 47K Ohm,
a 6222 would be 62.2K ohm).
In answer to your basic question, yes, you can usually cross reference or identify old
part numbers (unless they're proprietary, owned by the company numbering systems).
If you get hung-up. List markings on this site, and somebody can probably help you.