Topic: Came Across A 1974 U67 Capsule (Read 2317 times)

Derek Samuel Reese · « **on:** January 06, 2021, 03:17:09 pm »

I've come across what looks like a good quality U67 capsule from 1974.
It has never been re-skinned. There is a small amount of gold missing but the seller says it sounds fantastic when he compared it to his other vintage U67s.

I know from Klaus, saying looks aren't everything when it comes to a capsule, hearing is believing !!
Any thought on the pic's ?

Derek Samuel Reese · « **Reply #1 on:** January 06, 2021, 03:19:17 pm »

other side

Derek Samuel Reese · « **Reply #2 on:** January 06, 2021, 03:34:09 pm »

closer shot,
the rust I am seeing makes me concerned ? is that rust from the screw that transferred to the membrane ?
is it detrimental ?

Derek Samuel Reese · « **Reply #3 on:** January 06, 2021, 03:35:23 pm »

Sorry about the separate picture posts, they would all fit in a single post.

klaus · « **Reply #4 on:** January 07, 2021, 10:47:57 am »

Derek,
The capsule's pictures reveal corona oxidization. There was a period, In the mid-1970s, when a layer of the conductive gold sputtered onto the diaphragms tended to oxidize and form a corona-like halo, accelerated by the the electro-chemical reaction from the applied DC voltage. When corona oxidization is bad enough, the inner section of the sputtering can lose conductivity, so make sure that you test for increased steady-state noise when you encounter these capsules.

Derek Samuel Reese · « **Reply #5 on:** January 07, 2021, 12:46:34 pm »

Good to know thank you Klaus, so would it be wise to stay away from buying a capsule in this state ?
Kind of looks like it can only get worse over time.
The seller told me it sounded great and there wasn't any sign of noise.
I fear that this oxidation will continue to spread or even get deeper through singing.
I use a pop filter but over time this may become an issue.

klaus · « **Reply #6 on:** January 07, 2021, 05:50:47 pm »

Two options, aside of abandoning the prospect altogether:

1. Get a money-back guarantee so you can test the capsule yourself and confirm that it still performs to spec

2. Buy it cheaply enough so that a potential total loss does not hurt

With corona oxidization it's not entirely clear to me whether the process is continuous or whether, once damage is done as seen on your picture, it stops at some point. I don't think I'll live long enough to be certain.

Derek Samuel Reese · « **Reply #7 on:** January 07, 2021, 06:14:38 pm »

The seller is in Spain and doesn't want to do a money back guarantee, he wants $750 for it which is a great price if it sounds great, but this oxidation thing troubles me.
And if you don't know and no one else chimes in on this capsule i think I'm gonna pass and wait for one that is in better shape and closer to NYC.
Thanks as always Klaus

uwe ret · « **Reply #8 on:** January 07, 2021, 06:51:56 pm »

RE: Corona Oxidization:

How does the gold film, pure to permit sputtering, oxidize? I can see the deterioration, but is that really oxidation?

klaus · « **Reply #9 on:** January 07, 2021, 08:46:32 pm »

The question is not new: how could could gold corrode? I confirmed the issue with Berlin. There was some kind of substrate material used to bond the gold to the Mylar. That material over time had an electro-chemical reaction causing the corona oxidization.

Derek Samuel Reese · « **Reply #10 on:** January 07, 2021, 09:03:30 pm »

I did a little searching just on oxidation and i am sure there are many other and different factors that play in to this, but.. i asked Google What affects the rate of oxidation?
and the answer was----
A number of factors affect the oxidation rate, including temperature, pressure, crystal orientation, oxygen source (oxygen or water) and impurity doping.
So this tells me that when you sing into a mic it affects the temperature, the room affects the temp..
Pressure is a big one singing into a capsule, oxygen source, oxygen and water, from breath and spit.
My money tells me this will get worse over time.

klaus · « **Reply #11 on:** January 07, 2021, 10:11:43 pm »

Experience, in my book, beats Google/Wiki infos every time.

I've observed and dealt with the K47/67/87 corona defects since the late 1980s and have not found the issue getting worse with time; rather, the deterioration seems to arrest at some point.

But what do I know? Just spending the best years of my life with one type of corona or another...

Derek Samuel Reese · « **Reply #12 on:** January 08, 2021, 06:19:09 am »

I know experience is king, but sometimes Google is helpful.

Since the deterioration seems to arrest at some point, how does one find out what stage of deterioration it is in at the present moment?
The seller bought this capsule four years ago, showed me pictures of the original sale and the capsule looked the same.

I am going to ask again if he would allow me to install the capsule and listen myself.
Thanks again Klaus.

Two different pictures at different angles, four years apart:

gtoledo3 · « **Reply #13 on:** January 08, 2021, 10:03:59 am »

Quote from: klaus on January 07, 2021, 08:46:32 pm

The question is not new: how could could gold corrode? I confirmed the issue with Berlin. There was some kind of substrate material used to bond the gold to the Mylar. That material over time had an electro-chemical reaction causing the corona oxidization.

I read somewhere that some nickel (or mix that includes nickel) was used to enhance the bond of the gold. Possibly still being done. I think I read this on the old Neumann forum.

I am not sure that explains “corrosion”, but the discussion does bring it to mind.

panman · « **Reply #14 on:** January 09, 2021, 07:24:00 am »

Quote from: klaus on January 07, 2021, 10:11:43 pm

I've observed and dealt with the K47/67/87 corona defects since the late 1980s and have not found the issue getting worse with time in most cases; rather, the deterioration seems to arrest at some point, unless accelerated by environmental factors.

I have one Gefell(RFT) M71 capsule, that has a really heavy corona oxydisation. I have had it since 15 years and it still works perfect no change within all these years. So, I am leaning towards, what Klaus says.

Derek Samuel Reese · « **Reply #15 on:** January 09, 2021, 08:41:59 am »

Is it safe to assume that removing the lead wire could be a bad idea with the oxidation ?
I have this nightmare where I remove the lead wire and the membrane comes with it lol
and I scream nooooooooo.

klaus · « **Reply #16 on:** January 09, 2021, 01:18:39 pm »

A simple way to reduce your anxiety:
Unsolder the two diaphragm lead-out wires at the end where they go into the head. That way, the original connection at the center of the diaphragm remains undisturbed.

Just make sure to shield the diaphragms during soldering (with a cloth, old credit card, etc.) to avoid splashing flux onto them.

bits_ville · « **Reply #17 on:** January 10, 2021, 01:28:16 am »

An appropriately sized jewelers bag can be great for protecting the diaphragm from flux when soldering.

RuudNL · « **Reply #18 on:** January 10, 2021, 07:26:28 am »

IMHO it is never a good idea to remove the lead-out wires from a center terminated capsule, unless there is a very good reason to do this and you know what you are doing. (Bold added by K.H.)
Apart from the risk of a slipping screwdriver(!), there is also a risk of an uneven force on the membrane after re-attaching the lead-out wires again and fastening the center screw. The result can be 'wrinkles' in the membrane, when this is not done the proper way.

Derek Samuel Reese · « **Reply #19 on:** January 11, 2021, 08:53:57 pm »

I ordered a solder kit :-)
I really don't think I have the courage to do this.
I wish there was a way to test the sound of a capsule without having to solder but I know there isn't.

bits_ville · « **Reply #20 on:** January 12, 2021, 03:08:45 pm »

If you're in the LA area, or SoCal, I'd be happy to help, else, find someone local to you who has some experience working on microphones, preferably Neumann mics. (there are some basic but idiosyncratic elements, like getting the capsule safely in and out of the basket, that require some experience)

Derek Samuel Reese · « **Reply #21 on:** January 13, 2021, 08:51:23 am »

I appreciate the offer :-) I’m in NYC.

David Satz · « **Reply #22 on:** January 15, 2021, 10:34:06 am »

Two things stand out to me about this deal.

[1] OF COURSE the seller says that it's a fantastic-sounding capsule. There's even a chance that he believes what he's telling you. But I don't think it's predictable whether you'll agree with him or not if you buy the capsule. You may have very different ideas of what you want the microphone to sound like. Then you'd have no return privilege, and the capsule might be hard for you to resell, for exactly the reasons you are hesitant to buy it--only more so (the next customer would have to wonder why you don't want to keep it).

[2] You really do face some risk by trying to install the capsule yourself. The capsule _head_ of the U 67 (and related models) was designed to be replaced as a unit by someone without special repair skills--but not the capsule within the head.

I actually used to repair hi-fi equipment for a living, decades ago, and I got to be pretty good with a soldering iron for everyday work on consumer stereo equipment. But I don't do my own repairs on microphones or tape recorders! I want someone with lots of specific experience to be responsible for that--preferably the manufacturer. For Neumann microphones in the NYC area (where I live, too), an excellent alternative to Sennheiser USA, should you want one, is Tom Onofrio (onofriothomas@sbcglobal.net).

Derek Samuel Reese · « **Reply #23 on:** January 17, 2021, 08:43:33 am »

I couldn't agree more, if this were a few wires that were far away from a delicate capsule that would be different.
The only person I will allow to touch my u67 is Mr Klaus, I unfortunately had a terrible experience with Tom.

Derek Samuel Reese · « **Reply #24 on:** January 18, 2021, 08:05:00 pm »

I decided to take the chance and do this myself.
I have to learn somewhere, so I convinced myself that I could ruin this capsule, and sat with this idea for a few hours.

I decided to practice on the capsule that is already installed. I switched the capsule around.
Getting the capsule out of the basket was easy as I have done this before.
Then i realized that to remove the soldered wires all I have to do is lightly tap the already soldered wires with my new solder iron and they all came apart with ease.

Removing the screws was even easier but working in the space of a small capsule made me nervous lol but I did it, switched it around and didn't even need to use new solder to reattach the wires because there was already a small amount present on the wire so it was easy.
The fear was the biggest part but after I got over that, it was smooth sailing.

The enjoyment I got after doing this was really awesome: I loved the fact that I was able to do this myself.

Maybe I can convince Klaus to help me along my journey of understanding the inner workings of the U67 when he isn't busy.
Felt wonderful !
I wanted to add that I used a credit card to guard the capsule as I soldered :-)

klaus · « **Reply #25 on:** January 23, 2021, 12:11:46 am »

Quote from: Derek Samuel Reese on January 08, 2021, 06:19:09 am

Since the deterioration seems to arrest at some point, how does one find out what stage of deterioration it is in at the present moment?
The seller bought this capsule four years ago, showed me pictures of the original sale and the capsule looked the same.
Two different pictures at different angles, four years apart:

Looking again more closely: the two pictures (see reply #12) clearly show continuing deterioration since 2017.

Derek Samuel Reese · « **Reply #26 on:** January 23, 2021, 11:57:27 am »

I looked at the picture also and saw it also.
It kind of looks like the left picture has so much light showing through the capsule and the right picture doesn't have as much light, wondering if the deterioration may be the same.
The capsule is on its way to me so I look forward to testing it :-)
Also the other side of the capsule looks like it is in great condition so we shall see.

Derek Samuel Reese · « **Reply #27 on:** January 30, 2021, 09:04:12 pm »

Today I received the 1974 capsule which I installed this evening and a few things I noticed right away.

The output volume was much lower than my healthy capsule and on both sides.

Also the sound on each side of the capsule didn’t have the luxurious bottom end we all know and love from a great U67.

One side has a ground hum issue, the other is silent.
But overall considering that it is from 1974, this capsule is in good shape but it needs that good ol' fashioned Klaus love, probably a three point cleaning and who knows what else.
I took a chance.

I reinstalled my 1978 capsule that Klaus took under his wing and all is back to normal.
I am proud of myself for even attempting to solder both of these capsules successfully:-)
I certainly feels comfortable doing this and this opened my eyes to wanting to learn even more.

I could be a very good student hint hint,
Have a great night everyone.

Derek Samuel Reese · « **Reply #28 on:** February 03, 2021, 10:29:20 pm »

I am not sure what happened the other day when i tested my new 1974 capsule, but all is working beautifully.

I took a day away from testing and got a good night's rest and woke up with a fresh brain and started to test my 1978 capsule against the new 1974 capsule.
It is hard to tell them apart, they both sound great, and on each side:
The hum I reported is gone, the lower output volume on the 1974 capsule is now at the same output of my 1978 capsule.
I can't imagine I did anything wrong because there are only three wires to connect.

I am very happy to now have a backup capsule that sounds great, no more down time if one needs a cleaning :-)
Thank you Klaus for all of you advice and help as usual and everyone else for pitching in.

And I would also like to add that the gentleman who sold me the capsule is fffaustino who is also a member here.
I couldn't ask for a nicer more honest person to do business with, and he lives in Spain.
Thank you, fffaustino :-)))

fffaustino · « **Reply #29 on:** February 05, 2021, 06:36:25 pm »

Thanks for your kind words, Derek, and enjoy your capsule!

Alfredo (fffaustino at repforum)

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Author Topic: Came Across A 1974 U67 Capsule (Read 2317 times)