NOS NTE metal film resistors

[mikeram]

I'm getting ready to build #183 and noticed a lot of discussion on the importance of using vintage resistors when possible. The question of whether the new NTE HW metal film resistors are the same as the old ones comes up now and then. It is clear that they are not the same, but since seeing is believing, I thought I'd take a few pictures of some of the resistors I have and show the differences.

NET Metal Film front.jpg

The two packages on the left are the oldest ones I have. They are a shade brighter blue than the following style and are also longer.
The next style is shorter and darker but still has NTE in the large red diamond.
After that the NTE is outside of the diamond, still the same color, and shiny like the previous ones.
The next iteration is ROHS compliant. The color is the same as the previous one but if you look closely, the body is matt and only the colored bands have any shine to them. I don't know if they sound the same, but I hope they do (since I have some of them:-).
Finally, the last one shown is the matt metal oxide looking one that you can order or find on the shelves today. Notice that the color bands are dull and the color is different from the blue ones. If someone sells you "NOS" resistors that look like this, send them back!

NET Metal Film back.JPG

You can see the different printing changes on the back that go with each succession.

On a side note: I'm still missing the NTE 220K metal films for my build, along with the 2.2K, 3.3K, 150K Roederstein Mk3's, and the Draloric Carbon Film 5.5K, 100K, 180K and 24K signal resistors. I have an ok collection of NOS NTE metal films and other NOS parts if someone would like to do some parts trading. PM me if you are interested.

Thanks,

Mike

[GAStan]

Thank you for posting this Mike. I recently went through this on my 183(ish) build and never found a definite answer if the current production is metal film or metal oxide. Only that people were going by the finish on the resistors.

I reached out to NTE asking them to clarify prior to the holidays and have not received any reply so far. If I do hear back I will provide an update here. Maybe if they receive enough inquiries they will provide an answer.

[bepone]

GAStan nobody can asnwer this question, but you can find out by yourself..you need to destroy the outer protection in every type and compare to similar metal film , then you can see if is metal film or oxide. Technically metal oxide is named fully metal oxide film witch is also in short "metal film".

[dbharris]

Thanks for posting! It would be interesting to acquire a few of these in values that we don't use for amps and open them up to find out....

-Dan

[mikeram]

Bepone, I have enough of these that I'd be willing to use for the test, and I can get a set of new ones at my local electronics store. Any Idea how to effectively remove the outer protection without destroying the inner metal film?

Mike

[bepone]

Mikeram try with the pliers, crush gently until paint drops.. if i'm not mistaken metal oxide will have dull metal composition inside, and metal film for comparation will be shiny depending of the metal composition used..
I would buy few different metal films and metal oxides of 1w just to compare , and see about NTE

[jelle]

Hi Mike, I have Dralorics, and I messaged you, Jelle

[mikeram]

Bepone, Thanks for the instructions. I'll give that a try this weekend and report the results if I don't destroy them in the process.

Mike

[mikeram]

Well, I chose some resistors and did some scraping. here they are in the packs.

NTE metal film test 1.JPG

NTE metal film test 2.JPG

I tried to put them in what I think is their age timeline. The only ones I'm not sure about are the last two. The most resent ones are ROHS compliant like the 180K, but the 2.2K looks like the new ones on the shelf but does not have the ROHS stamped on the package. The weather didn't allow me to go to my local electronics store and purchase the newest style resistor, so I'll attach some final pictures once I can get it.

[mikeram]

Before scraping.

NTE metal film test 3.JPG

After.

NTE metal film test 4.JPG

The paint/covering of the 430K, 180K, and 2.2K came off fairly easy. The rest of them were pretty tough. The 2.2K seems to have a slightly thinner lead. Having never seen the inside of a metal film before, I learned something. The higher the resistance, the denser the inner bands.

As far as differences in composition, I'll let the experts chime in.

Let me know if I can provide different pictures that might help.

Mike

[ijedouglas]

That is super cool! Did the internals have any differences other than the spiral density? To me they all look similar except for the first one

[mikeram]

Ian, the one on the first one on the left is obviously darker and almost translucent. The second one from the left has a slightly different shade of color as does the one on the far right. Really, they were a lot closer than I expected. We'll see what the brand new one looks like when I get a hold of it. I wouldn't be surprised if it looks the same as the one on the far right.

Mike

[bepone]

Thx mikeram for the pics.. all material looks the same to me which is good, they didnt change the formula.

Mox -mf...difficult to say.. but need similar MF to compare for the same power handling..

Difference, mox is higher resistance material (oxides) and needs less turns for the same resistance than metal film, temp koef. is higher, aslo composite oxides have dull colors than MF composites

[dbharris]

Great work Mike! That is really interesting and would be great if the current production NTE are substantially the same as the older stuff.

Thanks!

-Dan

[mikeram]

Thanks so much for everyone who is interested in this experiment. I was finally able to get to my local electronics store, but unfortunately, they only had one new set of resistors in the values we've been looking at. Here is a pic of the shiny NOS 200K resistors on the left and the new off the shelf ones on the right.

200K Front.JPG

Front

200K-Back.jpg

Back