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[ssprod19]

Does anyone know at what point the C12 transformer switched from V2148 to T14/1.  The only thing I can find online says it happened in the earlier units.  Could the two versions be identified with serial numbers?  i.e. pre-500 are V2148 and post-500 are T14/1?

[klaus]

From my upcoming book "The Vintage Microphone Handbook":

"Three distinct generations of C12 can be identified, primarily by their visibly differing output transformers. The first one, from 1953 to about 1955, used the Hiller-made T14. A beefy looking affair, which, as mounted on the mic’s frame, barely clears the housing tube. (Postscript- 6-21-2016: This transformer is mysterious. I have never seen it in the flesh, despite Oliver Archut's insistence that it was used in the beginning of the C12 era.)

The next generation C12, including most ‘Siemens SM 204/23’-branded models, used the Henry Radio, model 2148, identified by that number on one side, and a black diamond painted on the opposite side onto lacquer-soaked brown cloth wrapping. These transformers can be found as early as 1954. Around 1958 the mic received its final transformer, the rather anemic looking T14/1, made by Haufe, near Frankfurt, Germany- the only transformer company that has been continuously supplying German mic manufacturers since post-war years through today. The last transformer version, by the way, was also used in AKG’s C24, ELA M 250/251, and C28A mic models." © Klaus Heyne, 2013 (Copying prohibited, unless copyright mark and author's name are attached).

[Jim Williams]

I've never seen an original Hiller, but always suspected the smaller versions after that had low end saturation problems. Low end THD in later 414's with those small output transformers is rather high. C-12 clones with larger laminates don't seem to have that problem. For years builders have used the 12/1 ratio Jensen DB transformer with good results.

[klaus]

T14/1 have been the output transformers of Telefunken ELA M251 and ELA M250 from day one.
I once installed an original T14 in an ELA M, and the result was sluggish and unexciting, tipping the balance towards "too dark".

Why mess with magic?

[ssprod19]

thanks for the info, Klaus.  From your experience, can the different versions generally be identified by serial number?  Or only by physically opening them up?

[klaus]

No official or unofficial record exists that would link AKG microphones with their serial numbers and their date of birth.

I never understood this. One would think that, for tax or accounting purposes, part of an annual inventory would be the listing of mics by serial number, as manufactured or sold in a given year. Latest when a company is taken over by new owners (that happened twice with AKG) a complete inventory list would normally need to be made.

Another complication: AKG's sloppiness with serial numbers. Serial numbers for mics were created for special customers upon special request, and often outside any number sequence of the mics of the era.

You can however accurately pinpoint the year of an older AKG mic if you are experienced: capsule generation, transformers, component, wiring characteristics, etc. were all unique for a given period.

If your C12 still has the original power supply that came with it: on N12 the exact assembly date is stamped to the frame accessible underneath the cover

[ssprod19]

very interesting, indeed.  I'll try to take a look at the PSU for the date.  Thank you, Klaus!

[rodabod]

Hi, can anyone identify the following C12 transformer? My guess is a Hiller, but I'm unsure.

Also, it has an O-pad attenuator fitted to the output which I have calculated to have around 10dB loss. I'm not sure if this would have been requested by the original owner, or added shortly after purchasing. Very simple to remove though.

[klaus]

A strong clue about the manufacturing date of the mic is the date on the silver 0,5mfd Siemens coupling cap. If you rotate that thing just a bit, or peek around on its back side, a manufacturing date will appear in black numerals. Add about 3-9 months, and you get the approximate date of manufacture for the mic.

This looks to me like a Henry Radio transformer. It has the cardboard insert with one of the three output connection choices visible: "500" for 500Ω, if I see this right. The earlier T14 (not T14/1) did not have that strapping choice printed on it, as far as I recall. But I have never before seen the attenuation circuitry surrounding the transformer. This could have been by customer special request  directly at AKG, or, skillfully installed afterwards by a third party.
 

[rodabod]

Thank you, Klaus.

It does indeed have markings for "500", "250" and what looks like "40".

I've just checked the 0.5uF Siemens cap, and it says "9.55".

I did look in the PSU for a date stamp, but I can't find one anywhere in either of my N12 PSUs.

Cheers,

Roddy

[klaus]

There is your answer: the mic was made around 1956, and its components, as shown on your pictures, would confirm that.
Best of luck with the mic!
KH

[rodabod]

Thanks again for offering your knowledge. It's very much appreciated.

[klaus]

P.S.: I have found these transformers sound best in the "500" (ohm) setting when coupled to most modern and many vintage high quality mic pres.

[J.J. Blair]

On an interesting note, the one time that I had a Henry transformer C12 here, I found the frequency balance extremely similar to my 251.  I usually find C12s to be a little thinner in the bottom end than my 251. 

Klaus, can you make a speculations about my impressions?

[klaus]

Not much to speculate:
The Henry transformer makes up a bit of the beef missing from C12 with flat dish CK12 capsules (not that many during the C12 days were made with deep dish) and T14/1 transformers. Whereas the ELA M, due to its capsule series, compensates what's lacking in the mid-lows with the somewhat anaemic T14/1. Both model combinations are favorites of mine.

Reading this, I feel like excluding those who are not that deep into the fine points of AKG product. So here is the simplified version:

When combining certain key components in condenser mics  (transformers with certain capsules or tubes, for example), shortcomings of any of the components standing alone can be mitigated, and the combination of components can lead to magical matches. The M7 and the first series of M49 transformers (those that were made for the Hiller MSC2 tube version) is another such magic combination.

[Ron McCaskill]

Hi all,
The purpose of the attenuator pictured in post #7  is the standard BBC 14dB attenuator (2x 470R in series, and 2x 560 in parallel in an "O" pad  configuration) which was fitted to BBC C12's to bring it's acoustic sensitivity down to match the 4038 mic. It also builds-out the output impedance to approximately 300 Ohms.
Regards, Ron.

[rodabod]

Ron, you are 100% correct. I didn't realise that it was fitted to match the level of the 4038!

[J.J. Blair]

Which transformer is this?

[klaus]

Hello J.J.,
The 3044 Henry transformer is a close relative of the widely used Henry 2148 model of the time, but with a different output impedance.

Greetings to Mr. Selmer

[aremos]

T14/1 have been the output transformers of Telefunken ELA M251 and ELA M250 from day one.
I once installed an original T14 in an ELA M, and the result was sluggish and unexciting, tipping the balance towards "too dark".

Why mess with magic?

Klaus,
When you state "an original T14" are you referring to the Hiller? And that the Haufe works better?

[klaus]

I am a bit confused about the connection between your citation of my post* and your question.

AKG used several transformer types and manufacturers for its large diaphragm tube mic transformers over the years, and each is of course "original" for that type of mic. But I found that some types do not readily interchange with others in AKG mics (hence your cited passage of my earlier post):
Despite its technical shortcomings the T14/1, for example, is the only transformer which retains a balanced frequency response and exciting timbre in AKG's ELA M mics. Likewise, an old Henry version in a late model C12 is not a symbiotic match either, due to the different capsule versions used.


* I just re-edited the wording of that old post because a whole line of text had been deleted in a previous edit. But the original message of that post remains the same: the less than ideal transformer (T14/1) is the original and only one I would recommend to use in the ELA M250/251 in order to retain the mic's spectacular sound.