Is it possible to limit the max post to say 100 words lol
<snip>... then i returned to the bench and started measuring the voltage drops across the diodes but the diodes had been damaged from heat removing them
So my question is which way round do these diodes go as there's no markings for polarity
<snip>
Since the diodes were damaged from heat removing them, you should carefully dip them in a fast-drying red colored varnish and deposit them in the trash. That way, if they should ever find their way back onto your work bench, you can immediately dispose of them again, saving hours of frustration trying to determine the polarity of a shorted or burned open diode. Or maybe go find that clown again and ask to borrow their lipstick...
Which reminds me of a story... I have been watching the first twelve seasons of
NCIS on Netflix (I have currently finished watching all twelve seasons twice, maybe three times... or was it four times? One of the nice things about getting older is I mostly forget TV shows and movies I've seen before, so they are like "new" to me again. My wife doesn't have this problem. In fact, she has the uncanny ability of "remembering" things she hasn't even seen yet, like a newly released movie that hasn't appeared in local theaters or on television yet. I don't usually mind this unless she shares her plot spoilers with me.), but I finally got bored and wanted to see how Gibbs survived getting shot. So I ordered up season thirteen on Amazon Prime. I have now watched up to episode six of season thirteen now, but found out on the Internet that
NCIS has been renewed for at least three more seasons. So that gives me plenty more time to practice telling stories in the manner of Dr. Mallard, although unlike the writers for
NCIS there is zero to no chance of getting paid for them.
So, having been prompted to answer a pithy question
vis a vis diode polarity, I dug back into my vast reservoir of extra long term memory and pulled out a galena-based point-contact diode, which I used in the previous century to construct a crystal radio set. The diode consisted of a small metal cup into which was soldered (using low-temperature solder) a small piece of galena crystal (lead sulfide), a common mineral associated with the mining of lead ore. A thin stiff wire, called a "cat's whisker" no doubt due to its resemblance in size to the whiskers on a cat, experimentally probed the surface of the galena to find a sensitive spot for rectification. From this mechanical arrangement the symbol for the diode rectifier was born: the galena crystal was the cathode and the thin wire making a point contact became the anode. It is happy circumstance that the triangular head pointing at a straight line also represents the direction of conventional current flow from positive to negative, anode to cathode.
Not that this mattered a fig to a kid trying to find the "sweet spot" and tune in a local AM broadcast radio station. It was many years later that I discovered this type of diode was actually a Schottky diode, and only just recently discovered what part was the anode and what part was the cathode.
This Wikipedia article will tell you more than you ever wanted to know about it.
The above image (copied from the Wikipedia article) is pretty much identical (as I recall it) to the cat's whisker detector I used for my first crystal radio. Years later I was able to acquire some real commercial crystal diodes, type 1N34 germanium. No fuss required to get these to work in a crystal set. And years after that, while serving in the Air Force, I discovered that gigahertz diodes in ceramic packages were made with point-contact diodes. We used them in our Ku-band radar as mixer diodes. You could tell they were point-contact because there was a tiny screw in the end, cemented in place so it couldn't move, that if you tried to "adjust" the screw prevented the diode from ever working again. Here's a picture of the internals:
By now it should be obvious that close inspection of opaque plastic or glass-encapsulated diodes or stud-mounted power diodes will reveal almost no clue as to which end is the anode and which other end is the cathode. Applying voltage through a current limiting resistor and noting which polarity results in conduction is the only certain way that I know of to determine diode polarity... if the diode isn't defective. And if the diode is defective, a pair of vice-grips can make sure you never accidentally try to use it again. Some spiffy multi-meters have a diode test function that actually measures the forward voltage across a diode by applying a small current to the diode. This is mighty useful for distinguishing between silicon and germanium diodes.
As for a 100 word limit... well, if you have read this far, clearly you aren't serious about that.
Hop
