1N4148 diode spec's - Page 1
Forum section: electronics / repair

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: June 14, 2024, 01:32:12 am
content: I seem to remember some had different voltage ratings?Is there a way to tell in the markings or were these fake parts?Working on a Peavey CS-800 amplifier for a friend who is suppling parts, I received a batch of 1N4148's from him.These were marked V 4148 and were slightly smaller than ones I was replacing so it made me think to test them.At slightly over 40VDC these exploded open, others I had in stock were still fine at slightly over 60VDC, these weremarked H 1N4148.Can you guess what would have happened if I had used what he got without testing them.

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 14, 2024, 02:29:29 am
content: Quote from: Jeff eelcr on June 14, 2024, 01:32:12 amYes, somewhere between 75V to 100V.Quote from: Jeff eelcr on June 14, 2024, 01:32:12 amNot really in practice. Most just got generic marking.Quote from: Jeff eelcr on June 14, 2024, 01:32:12 amDepends on where and what the diodes are supposed to do.Are you sure there's nothing else wrong with your gear? Engineers don'tusuallydesign commercial product in such a way that stress a generic jelly bean part anywhere near their limit.

author: Kim Christensen
author_rank: Super Contributor
timestamp: June 14, 2024, 02:31:10 am
content: Probably fakes...The Vishay ones marked V4148 are rated for 75VWhat would have happened? Maybe nothing. Depends on the circuit and if they'd get reversed biased with more than 40V.Best to not use them though. Who knows what the other specs are.

author: DimitriP
author_rank: Super Contributor
timestamp: June 14, 2024, 03:31:16 am
content: QuoteYes, you would stop accepting "friend supplied parts" in the fist placeOr as they are known in other circles: "customer supplied parts"On a different note..Peavy sure like their diodes !!!

author: MathWizard
author_rank: Super Contributor
timestamp: June 14, 2024, 05:41:55 am
content: I forget I should never really trust ebay/amazon parts. I've said it before but never did it, I should test some of my diodes and BJT's. I mainly get brand name electrolytic caps these days, and I can think of a few old things I made that should get better caps too.

author: chilternview
author_rank: Frequent Contributor
timestamp: June 14, 2024, 06:18:42 am
content: You don't mention how you were testing them when they blew up, but I'd expect that to happen if you didn't have a resistor of at least 10k in series with them when you applied the 40v, to limit the breakdown current. Else they become a fuse.

author: Gyro
author_rank: Super Contributor
timestamp: June 14, 2024, 08:22:39 am
content: Quote from: chilternview on June 14, 2024, 06:18:42 amWhilst a 10k resistor would prevent the diode from shattering when it avalanches and is good practice, the fact that it does so at just 40V means that it is a fake (probably scooped out of the parametric test fail bin at the factory). You could argue that it avoid the need to mangle the leads before throwing it in the bin - my usual practice with faulty parts.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: June 14, 2024, 09:05:00 am
content: Peavey quote that replacement 1N4148 diodes in their equipment should be rated 75v, 10mA.

author: David Hess
author_rank: Super Contributor
timestamp: June 14, 2024, 10:51:03 pm
content: Quote from: MathWizard on June 14, 2024, 05:41:55 amIt is the exception when I get a genuine part from Ebay or Amazon.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: June 15, 2024, 12:59:38 am
content: I did not mean the different spec's different voltage, the reverse voltage rating (75V) and the peak pulsed reverse voltage (100V)on a normal 1N4148 is on the same part.What I remember is a 50V rating by some manufacturer maybe a mistake?

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: June 15, 2024, 01:10:00 am
content: Kim, the V4148's are the exploding ones, my intension was to test to over 50V never got that high on those.My stock exceeded 60V no problem.I could mark them for car stereo only, if other spec's hold up.