Topic: came across a 1974 u67 capsule (Read 668 times)

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

Ive come across what looks like a good quality u67 capsule from 1974.
It has never been re-skinned, theres a small amount of gold missing but the seller says it sounds fantastic when he compared it to his other vintage u67's.
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 aborting 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 down the road does not hurt

And, speaking of "down the road": it's not entirely clear to me whether deterioration through oxidization is continuous or whether, once damage is done as seen on your picture, it stops at some point. I just don't 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 »

Quote from: klaus 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.

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 »

I am aware of the question - how could could gold corrode?- and 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 look-up 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 one point.

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

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

I am aware of the question - how could could gold corrode?- and 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; rather, the deterioration seems to arrest at one point.

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.) Emphasis 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 10, 2021, 01:27:27 pm »

A jewelers bag ? Do you mean that small satin pouch ?
I think for soldering this I might do it the poor mans way, heating a flat head screwdriver and using the tip as a soldering iron and gently attach the wires

klaus · « **Reply #20 on:** January 10, 2021, 02:13:14 pm »

That's NOT recommended.
That way, you would heat up way too much way too far from the object. Get a decent electronic solder station, learn how to properly solder (practice on something cheaper than a $1k capsule!), or give the job to someone who knows.

RadarDoug2 · « **Reply #21 on:** January 10, 2021, 02:37:05 pm »

Quote from: Derek Samuel Reese on January 10, 2021, 01:27:27 pm

I think for soldering this I might do it the poor mans way, heating a flat head screwdriver and using the tip as a soldering iron and gently attach the wires

Where on earth did you get that idea from? Thats one of the oddest things I have ever heard!

Derek Samuel Reese · « **Reply #22 on:** January 11, 2021, 06:58:04 pm »

Because the heated screwdriver doesn't get nearly as hot as a soldering iron would to prevent the splashing if the solder.
The screwdriver gets just hot enough to melt the solder but never splashes.
It was just a thought but you all know whats best and I will certainly listen

klaus · « **Reply #23 on:** January 11, 2021, 08:11:11 pm »

Not to belabor this, but you would be surprised how little heat the tip of an electronic soldering station actually distributes beyond the area it needs to heat up (the very point of precision soldering stations).

A screw driver would need to be heated up quite a bit, and over a large area, to overcome the heat sinking it presents to any heat applied.

Derek Samuel Reese · « **Reply #24 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 #25 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 #26 on:** January 13, 2021, 08:51:23 am »

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

David Satz · « **Reply #27 on:** **Today** at 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).

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Author Topic: came across a 1974 u67 capsule (Read 668 times)