AKG C12 / Siemens SM204 help needed

[granger.frederic]

MSVienna is referring to the fact that the acrylic is cracked in multiple places. It's very likely that the capsule was exposed to alcohol.

Exactly!

or it's just the effect of time and different thermal expansion  of the metal (screws , backplates, peripheral ring) and the acrylic ...
the elasticity modulus of the perspex tends to decrease with time , it has also a poor low and high temperature resistance and a poor fatigue resistance
add that all the parts in the CK are mechanically tensioned
after 40 years , with sometimes brutal thermal variation , cracks occurs ...
perhaps less with the "red version" of the CK12 material , Tim could confirm  ?
Maybe that's why AKG came to Teflon in the next capsule revision ...
I have a CAD CAM/CNC machine at home , and i often think about milling that part inside a hybrid ceramic block (composite with 80% of ceramic) that has very good mechanical /chemical /electrical properties...

 

[TLRT]

Hi All,

I don't mind this conversation here, there are pretty useful things which is new to me,as I don't have much experience with those vintage stuff. Looks like the capsule will have a probem, it was cleaned by a local "expert". Could somebody explain to me how this S36 pattern selector is working if it has 5pin input and 3pin output? How the mic will work properly with only 3pin, and what are those voltages?

 

[Tim Campbell]

Oh dear. Well at least there are plenty of people to choose from to return that to original condition for you.

 

[micaddict]

I've learned a lot today.

Not so much about capsules, mind.

 

[ln76d]

Hi All,

I don't mind this conversation here, there are pretty useful things which is new to me,as I don't have much experience with those vintage stuff. Looks like the capsule will have a probem, it was cleaned by a local "expert". Could somebody explain to me how this S36 pattern selector is working if it has 5pin input and 3pin output? How the mic will work properly with only 3pin, and what are those voltages?

Oh men, you need to change your local expert, if he did that to your capsule...

For the pattern selectors - S36 is a completely different beast than C12 selector.
Probably you could sold S36  for really good money and make new switch for C12.
Conversion is really unprofitable, since C12 pattern selector is only a box, few resistors, one capacitor, two connectors and a piece of wire.


http://www.9voltstudio.se/akg_s36_repair_1.jpg
vs.
http://groupdiy.com/index.php?action=dlattach;topic=44737.0;attach=22472;image

 

[TLRT]

Hi All,

I don't mind this conversation here, there are pretty useful things which is new to me,as I don't have much experience with those vintage stuff. Looks like the capsule will have a probem, it was cleaned by a local "expert". Could somebody explain to me how this S36 pattern selector is working if it has 5pin input and 3pin output? How the mic will work properly with only 3pin, and what are those voltages?

Oh men, you need to change your local expert, if he did that to your capsule...

For the pattern selectors - S36 is a completely different beast than C12 selector.
Probably you could sold S36  for really good money and make new switch for C12.
Conversion is really unprofitable, since C12 pattern selector is only a box, few resistors, one capacitor, two connectors and a piece of wire.


http://www.9voltstudio.se/akg_s36_repair_1.jpg
vs.
http://groupdiy.com/index.php?action=dlattach;topic=44737.0;attach=22472;image

OK,sorry I thought about the SM204's original pattern switch... I checked your picture now I understand

 

[tonzauber]

Hi All,

I don't mind this conversation here, there are pretty useful things which is new to me,as I don't have much experience with those vintage stuff. Looks like the capsule will have a probem, it was cleaned by a local "expert".

Ouch.... I'm cringing in pain.....

 

[TLRT]

Hi All,

I don't mind this conversation here, there are pretty useful things which is new to me,as I don't have much experience with those vintage stuff. Looks like the capsule will have a probem, it was cleaned by a local "expert". Could somebody explain to me how this S36 pattern selector is working if it has 5pin input and 3pin output? How the mic will work properly with only 3pin, and what are those voltages?

Oh men, you need to change your local expert, if he did that to your capsule...

For the pattern selectors - S36 is a completely different beast than C12 selector.
Probably you could sold S36  for really good money and make new switch for C12.
Conversion is really unprofitable, since C12 pattern selector is only a box, few resistors, one capacitor, two connectors and a piece of wire.


http://www.9voltstudio.se/akg_s36_repair_1.jpg
vs.
http://groupdiy.com/index.php?action=dlattach;topic=44737.0;attach=22472;image

It was a joke, we bought the mic like this. Now we have to decide if we reuse our vintage N12 for this project, or I will use my own DIY PSU with an internal pattern switch. It will probably stay here with us in the studio, so it is more convenient to use a "modern" PSU.

 

[tonzauber]

it should not be too difficult to build a pattern switch for the N12.
It is basically a rotary switch with 9 400kOhm resistors.... 1 mOhm Resistor and a cap... some wires, connectors and you are done
Just look at the right hand side bottom of the attached schematic.

However, a more modern PSU has its merits as well...

 

[ln76d]

Early version were 50k and from schematic looks like 0,4M is for pot or rheostat since is lin. and in brackets 0.5M "wid." is for widerstand  - resistor. Anyway it's only divider 

 

[micaddict]

Welcome to this forum, Klaus. 



Henk

 

[Tim Campbell]

Welcome Klaus. Good to have you here.

Here's a repair I did on an SM204

 

[tonzauber]

Can we get real?
The ORF broadcast version of the C12 seems to be the flavor du jour (worthy of a whole thread by the cognoscenti on this forum).

It's 100% identical in layout and components with the C12 of the same era, except for cathode biasing on an unknown number among them.  I own two original ones with 100% original components, and have worked on a few more. None had cathode biasing.

P.S.: The capsule in the pictures is shot and  cannot be restored with its original components.

Hi Klaus,

are they named SM 204 or SM 204/23 ?

Because if they have the /23 designator they should be with the cathode biasing.

 

[MS Vienna]

One thought on the "23" suffix: I haven´t seen yet an SM204 without "/23". I once was told that the "23" is sort of a customer code for some mics built exclusively for the ORF.  It seems that the known SM204 specimens differ from C12s of that era in the use of a Rohde & Schwarz transformer.
I cannot personally confirm this explanation of the "23". However, a friend of mine owns a C24L (MKII SerialNr. 7xx) that came with a PSU "N24S/23". The C24L was definately a special ORF version and came with a black custom swivel mount fitted with a LEMO connector.

Regarding capsule repair I think it´s reasonable to repair a damaged capsule back into working condition if it´s a workhorse mic.
If the owner sees the microphone as investment too then a completely new replacement capsule like a CT12 might be preferable to a mere repair of the original which lowers the mic´s resale value considerably.  True restorations for those old CK12 might become available at some point and an untouched/unrepaired capsule would be a better start here since all third party repairs at least leave their own signature look unique to the individual repairman (e.g. surface treatment different to the original techniques ect.) Most likely a real restoration that uses the original techniques will be more expensive anyway than any of the new CK12-inspired capsules currently available. If signs of previous repairs have to be removed on top of that the cost of such a restoration can easily explode - as often witnessed with restorations of valuable old instruments. 

 

[MS Vienna]

Universal PSU N6128/23

 

[tonzauber]

I would like to disagree. Have a look at the schematic I posted on page 1 of this thread:

http://groupdiy.com/index.php?action=dlattach;topic=62801.0;attach=42858

The whole drawing is labelled "Gesamtschaltung C23 (Umbau C2)" -> "Complete Schematics C23 (Modification C2)", dated 21.12.1960.

The mic is called AKG C23  and below in small letters SM204 / 23.

It also makes sense in another way: C23 mono, C24 stereo, both cathode biased, hence the C23 is compatible with the C24 PS which does not offer the biasing voltage. (which, in my guess, is the reason for the modification in the first place, to make it easier for broadcasters who use both).

But maybe it's all coincidence,

 

[micaddict]

That's interesting info.

Any idea why AKG wanted to go with a smaller tranny (inside the same body)?

Perhaps they anticipated a smaller body?

 

[ln76d]

But that would not explain why AKG bought much larger transformers than the mythical "T14" from the Vienna company Henry for several years before switching to the T14/1.

Maybe you have T14 and could share some pictures here?
Also wasn't the Hiller T14?

 

[MS Vienna]

That's interesting info.

Any idea why AKG wanted to go with a smaller tranny (inside the same body)?

Perhaps they anticipated a smaller body?

Mr. Wolf once told me that the T14/1 has preferable technical properties in some aspects to the formerly used transformers and was chosen for that reason.
As a side effect it didn´t hurt to have one transformer model that could be used in most of the C-mics that were produced at that time (C28, C24, C12, M251)

 

[ln76d]

Was I not clear in my previous posts that I have never seen a T14, and that I now believe that this thing may never have existed, aside of maybe a prototype or very early C12?
Yes, Oliver referred to it as Hiller-made. But he is dead and cannot be queried any longer.

Maybe you was, but somehow i missed that post, i will look later

EDIT: Sorry, I read your post totally mistakenly - i was sleepy as hell

Somehow i always was surprised about all these "whole world original laminations" of tab funkwerk transformers and their T14 seems to be another product which no one can proved  is it at all close to the original - if original ever exist ( i also doubt).
I know only that hiller used ct m14/1 transformer in their 159/160 microphones.

http://images.yuku.com.s3.amazonaws.com/image/jpg/54f10c0b4ebe08.59951734_r.jpg

From the pics it looks similar to t14 - t14/1 type (like many others transformers from same era - for example schoeps) .
http://www.radiomuseum.org/r/hiller_m159.html
Anyway on the pics it looks bigger than Haufe t14/1 but this can be illusion becuase hiller bodies were really small.
I will look later for my hiller bodies and Haufe t14/1 and try compare it to the pictures.