AKG CK12 Capsule Revisions

[chrisregent]

Hello everyone,
I have been trying to read up about the various revisions of the CK12 capsule over its life. I am not talking about any of the plastic capsules (which are not CK12) I'm specifically looking at the machined brass type that there are now several copies of.

Ashley Styles (Saturn Sound) has the interesting disassemblie photos and description but as we are told by various sources on the internet there were 11 different revisions of this capsule.

So can we get a proper list of what these revisions were? As far as I can tell some of these changes were mostly material differences.

So let's see if we can fill in the blanks?
we know that some of them had different color plastic/paint.
It has also been mentioned that they changed the diaphragm from 10um to 6um...
We know that spacer thicknesses were changed. (Though my assumption is that this would be varied on a capsule by capsule basis for tuning)

Revision:
1. 1953 Shallow Chamber - diaphragm gap 40um - 10um diaphragms Stryroflex - 800Hz
2. 9um Mylar diaphragms
3. 1955 - 9um Mylar diaphragms
4. 1959/60 Deep Chamber - diaphragm gap 60um - 9um diaphragms Mylar - tuning?  Approx 3db sensitivity increase
C12A 1961
5. Red Paint?
C414ecomb 1972 defiantly red at this point.
6. 1966/7/8/9 6um diaphragm Mylar?
7.
C414EB 1976
8.
9.
10.
11.

It has been suggested that it was the late sixties that the diaphragm was changed to 6um Mylar.

At any point in the history of the CK12 were the inner delay plates made from plastic? Advised answer is No.
Was the paint introduced to seal the two halves of the capsule together?
Do we have any technical drawings of the capsules?

I will update as we go along.

I'm very excited to see what we come out with.

ADDED:
So we have a "narrow/shallow/flat chamber/dish" and there is a "deep chamber/dish" what do these specify?

 

[gyraf]

The Saturn Sound pages are probably the closest you get to an authoritative list - there's a lot of rumours and misinformation around about this capsule.

Quite a lot can be learned from the later plastic types as well - not only what aspects to avoid.

Are you planning to make your own CK12? In that case, prepare to spend the next 10-15 years tweaking and listening...

Jakob E.

 

[chrisregent]

Hi Jakob,
I am trying to document the changes of the CK12 brass capsules to remove any myth and hocum surrounding them. To get the information into one concise document.

From what I can see so far there are two major revisions, that were the shallow and deep dish or chamber versions. But what exactly does this entail? For example is it the depth of the chamber or is it the diameter of the chamber behind the backplate.

Ashley's pages show some interesting parts, but omits the design of the delay plate.

Best,
Chris
Edit auto correct!

 

[ln76d]

What's the "Red Paint"?

 

[chrisregent]

Some of the capsules had their plastic section painted red around the outside.
I wonder if this was to seal any potential air gaps.

 

[ln76d]

Like this?

https://www.gearslutz.com/board/attachments/high-end/276896d1329134055-original-brass-capsule-ck12-akg-c414-1.jpg