What are the chances these are real? - Page 1
Forum section: electronics / general

author: BillyO
author_rank: Super Contributor
timestamp: May 16, 2024, 02:48:21 am
content: They look real ...https://www.ebay.com/itm/392633261916?

author: Kim Christensen
author_rank: Super Contributor
timestamp: May 16, 2024, 05:11:03 am
content: You can buyLM741 from Digikey...So why bother with eBay?

author: pcprogrammer
author_rank: Super Contributor
timestamp: May 16, 2024, 05:35:38 am
content: Or if you like the gamble you can get them cheaper on Aliexpress.Edit: And the the IC's the ebay picture shows are 8 pin dip and not 14 pin dip like the title offers (LM741J-14) Those are harder to find onAliexpressand more expensive, but less than the single piece in that ebay add.

author: Haenk
author_rank: Super Contributor
timestamp: May 16, 2024, 09:30:59 am
content: Judging by the negative feedback, they *do* sell fakes. I therefor would consider positive feedback rather as "the buyer did not notice the fake".So expect to receive not the stuff you purchased. Buying OPAMPs from China is pointless.

author: Ice-Tea
author_rank: Super Contributor
timestamp: May 16, 2024, 10:35:11 am
content: Quote from: Kim Christensen on May 16, 2024, 05:11:03 amBecause these are from '88 and some people will only accept era-correct replacements?

author: BillyO
author_rank: Super Contributor
timestamp: May 16, 2024, 02:17:19 pm
content: Quote from: Kim Christensen on May 16, 2024, 05:11:03 amSure you can, if you want LM741C, but the one I linked to is the LM741J. The 741C is just the run-of-the-mill 36V part. The 741J is the mil-spec 44V part. You also can get theLM741Jfrom Digikeytoo, but it's 5 times the price of the one I linked on eBay.When you need 44V, 36V just won't do.

author: BillyO
author_rank: Super Contributor
timestamp: May 16, 2024, 02:21:37 pm
content: Quote from: pcprogrammer on May 16, 2024, 05:35:38 amYeah, don't know what's up with that. Kind of has "pass on this" all over it. a 14 pin version will not fit the available space.

author: Kim Christensen
author_rank: Super Contributor
timestamp: May 16, 2024, 03:37:22 pm
content: Quote from: BillyO on May 16, 2024, 02:17:19 pmTrue, but if I needed 44V specs, I'd simply buy a different OpAmp rather than the LM741J...I can see the case for keeping retro equipment as close to stock as possible. But for everything else, I'd find a more modern OpAmp.

author: BillyO
author_rank: Super Contributor
timestamp: May 16, 2024, 04:26:19 pm
content: Quote from: Kim Christensen on May 16, 2024, 03:37:22 pmI need a DIP-8 package. I guess I could get some other 44V OpAMp and use a carrier/breakout board. But none of them are cheap either and then you have the expense of the chip carrier and the additional work (not so bad tho..).

author: Shock
author_rank: Super Contributor
timestamp: May 16, 2024, 06:19:14 pm
content: Looks cheaper ordering directly from TI.Buying a nos military spec part from china on ebay is laughable.

author: BillyO
author_rank: Super Contributor
timestamp: May 16, 2024, 06:29:15 pm
content: Quote from: Shock on May 16, 2024, 06:19:14 pmOnce you include shipping costs (I'm in Canada) it's not that much less. My best bet is to wait until I have enough to order from digikey so that I get free shipping.

author: Kim Christensen
author_rank: Super Contributor
timestamp: May 16, 2024, 07:48:11 pm
content: Quote from: BillyO on May 16, 2024, 04:26:19 pmIf you can find a carrier/breakout board for cheap (Could also design/order a custom one from JLCPCB), then something like theTJM4558CDTcould work unless you need the offset null pins from the 741...

author: BrokenYugo
author_rank: Super Contributor
timestamp: May 16, 2024, 08:03:11 pm
content: The op amps in particular are virtually all fake on Chinese marketplace sites, if they;re working opamps they won't match the datasheet for the part number. With ceramic package ICs you might have better chances to get the real thing, but it's going to be a beat up used part, exposed to ESD, solder dipped legs, etc. low grade salvage of last resort.

author: thm_w
author_rank: Super Contributor
timestamp: May 16, 2024, 09:07:34 pm
content: Quote from: BillyO on May 16, 2024, 04:26:19 pmsmd to thr adapter boards are incredibly cheap, pennies:https://www.aliexpress.com/item/1005002776733692.htmlIs this a design or a repair. If its a design you've possibly painted yourself into a corner with all these niche specs, that may or may not be needed.

author: BillyO
author_rank: Super Contributor
timestamp: May 17, 2024, 12:09:55 am
content: Quote from: thm_w on May 16, 2024, 09:07:34 pmIt's neither and both.I'm trying to get one of those half baked Highland power supplies working properly. It's easy enough to limit the current through the pass transistor to get it in spec but then you are still faced with the op-amps being supplied too much voltage. The original design calls for TL081 for all 3 of them. However, the current error amp and the voltage error amp are being supplied with as much as 40V when current draw is low. The voltage refence is okay and the voltage error amp requires offset adjustment.Options:Exchange the 2 over run OpAmps for LM741J - simple but more costlyRun the positive supply for the current error amp from the 24V fan regulator and just replace voltage error amp with a LM741J - a bit more work, but cheaperJust use a 20V transformer (instead of 24V), adjust the gain of the voltage error amp to give 25V full-scale and use cheap TL081s all round and end up with a 0-25V and 2mA to 3A power supply - cheaper and simple but only a 75W supply instead of a 90W supplyI think I will go with option #3.

author: thm_w
author_rank: Super Contributor
timestamp: May 17, 2024, 12:25:48 am
content: Some discussion here:https://forum.allaboutcircuits.com/threads/power-supply-kit-supply-voltage-on-tl081.128351/https://electronics.stackexchange.com/questions/520653/how-to-find-a-pin-to-pin-replacement-for-tl-081-but-with-higher-vccMaybe the negative rail voltage can be reduced?

author: BillyO
author_rank: Super Contributor
timestamp: May 17, 2024, 12:33:30 am
content: Quote from: thm_w on May 17, 2024, 12:25:48 amThat's option 4 and not too hard to do, but you'd still need a negative rail of about 3V so that would just save 2V - not really enough but would certainly extend the life of the OpAmps. You'd still have to deal with pass transistor. The operating envelope has the possibility of it dissipating 100W. That's it's AMR. SO all in all a PS living on the edge. I'd like to have it "safe at all possible speeds" (Sorry Ralph)

author: temperance
author_rank: Super Contributor
timestamp: May 17, 2024, 01:06:25 am
content: QuoteSo you don't want a genuine LM741 from some reputable distributor but a fake LM741 ebay because it says mil-specThis is probably the best joke ever posted in here.

author: BillyO
author_rank: Super Contributor
timestamp: May 17, 2024, 01:15:46 am
content: Quote from: temperance on May 17, 2024, 01:06:25 amIs this the winner of the Dunning-Kruger award?No. The LM741JISthe mil-spec part. Whether I get it for $5 or $30. If I can get it from Yun Hung-Lo for $5 and it's genuine, then why not? They have been making these for 4 decades or more, so presumably there is some cheaper NOS around somewhere.So, no, I'm not considering buying it from the eBay ad because they say "mil-spec", but I'm considering it because it's an LM741J.Shall we await your next silly, un-researched and self-embarrasing outburst, or are you done for the night?

author: exmadscientist
author_rank: Frequent Contributor
timestamp: May 17, 2024, 02:01:59 am
content: The newishTL081His good to 42V abs max and might be worth considering. (SMD only, though.) Those on DIP adapters plus a 40V-ish zeners across their supply pins might be a reasonable quick fix.

author: temperance
author_rank: Super Contributor
timestamp: May 17, 2024, 04:32:48 am
content: QuoteBeware, here is the next outburst. I did read what you wrote looking for clues as to why you would consider a probably fake mil-spec op amp from ebay but could find a valid argument.QuoteJust calculate the cost of buying fake op amps including your additional work. It doesn't make sense.-2 or 3 fake op amps @ $4.5 each.-Soldering them into the board.-It doesn't work. Darn, is it the op amp or did I make a mistake? Time for some debugging. The op amp are fookin fake. I've been ripped off.-Desolder the op amp.-Search for a proper solution.-Back to square one. Angry now.-Order parts.-Solder in new solution.-It works but those suckers ripped me of. Must complain somewhere about that. Didn't get my money back.https://www.digikey.ca/en/products/detail/dfrobot/FIT0290/6588424SMD to DIL for about 80 cent including pin headers combined with an MC33072ADR2G for about 62 cent will do the job. And in SO8 I will probably find more 44 V capable op amps.

author: ledtester
author_rank: Super Contributor
timestamp: May 17, 2024, 05:17:19 am
content: Quote from: BillyO on May 17, 2024, 12:09:55 amIn this blog post:https://www.paulvdiyblogs.net/2015/05/tuning-030v-dc-with-03a-psu-diy-kit.htmlthe author uses TLE2141's which have a 44V operating range.In the comments someone mentioned using a MC34071.Here's another forum thread on that circuit:https://www.eevblog.com/forum/beginners/0-30v-0-3a-psu-audiogurus-version/

author: tooki
author_rank: Super Contributor
timestamp: May 17, 2024, 09:33:01 am
content: Quote from: BillyO on May 17, 2024, 01:15:46 amI don’t think Dunning-Kruger means what you think it means…Quote from: BillyO on May 17, 2024, 01:15:46 amThey weren’t disputing that the LM741J is the mil-spec part. They’re pointing out how incredibly naive it is to believe you’d actually get one from a vendor in Shenzhen at a fraction of the real price. The listing isn’t even consistent in what it’s for — the listing details say “OP497GSZ” (a completely different op amp).Of course there’s a (technically nonzero) chance the seller actually has legit parts, but it’s really unlikely.Quote from: BillyO on May 17, 2024, 01:15:46 amThey weren’t the ones responsible for a “silly, un-researched and self-embarrasing outburst”, that would actually be you…

author: BillyO
author_rank: Super Contributor
timestamp: May 17, 2024, 05:43:24 pm
content: Quote from: temperance on May 17, 2024, 04:32:48 amSo instead you thought it best to ridicule me? Nice.

author: BillyO
author_rank: Super Contributor
timestamp: May 17, 2024, 06:01:51 pm
content: Quote from: tooki on May 17, 2024, 09:33:01 amSo, I can tell from the rest of your post that reading comprehension may not be your strong suit, but it is interesting nonetheless.At what point in this thread did I actually state a belief that I could get a real LM741J from the ebayer I posted a link to? In fact I think it's fairly obvious I was making light of something I found in an ebay search.But just let me ask a question. Does it make you feel better about yourself to try to belittle someone on the internet, just because you cannot grasp the gist of their comments, by callingthemnaïve?You and temperance. Big people. Nice people for sure.

author: BillyO
author_rank: Super Contributor
timestamp: May 17, 2024, 06:07:38 pm
content: To the rest of the folk that did not misinterpret my first post and understood what I was really looking for, thank you for all your great ideas.I've decided to proceed with option 3 as I stated above.I'll exit this thread now as it seems the local twats have shown up.

author: tooki
author_rank: Super Contributor
timestamp: May 18, 2024, 12:09:33 pm
content: Quote from: BillyO on May 17, 2024, 06:01:51 pmOh, please, by all means do tell me what it is that I've missed.Remember, we can only go by what you actually wrote, not what you thought in your head.Quote from: BillyO on May 17, 2024, 06:01:51 pmNothing in any of your posts indicates that you seriously suspected it's fake. The thread title asks, and your subsequent replies argue from a point of being real.Quote from: BillyO on May 17, 2024, 06:01:51 pmI said:Quote from: tooki on May 17, 2024, 09:33:01 amI didn't callyou, specificallynaive. This is an example of the English "generic you", i.e. a synonym for "one". That sentence is synonymous with "They’re pointing out how incredibly naive it is to believeone wouldactually get one from a vendor in Shenzhen at a fraction of the real price."You're the one who dragged down the discourse with calling people Dunning-Kruger recipients (which you don't understand the meaning of), "twats", and of having "outbursts" when it's actually you having them.