R/E/P > Klaus Heyne's Mic Lab

Why no LDCs based on the AC701(k)?

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The title says it all, and while I recognize that the AC701 was designed as a miniature tube for SDC applications, why was it not used in an LDC? 

Or maybe it was and I am totally missing something.  It's such a beautiful sounding tube, I bet it would excell in large diaphragm format!

-Terrence Town

It was like with M49, many others also I think but that came to my mind first


Edit. Should be

Matti Lehtonen

Here is a partial list of large diaphragm microphones that were designed for AC701:

AKG/Telefunken ELA M250/251 (i.e. the main large diaphragm mic made by AKG at the time)
Neumann M49, M249, M269 and derivatives, SM69 (i.e. aside of the U67, all large diaphragm mics made by Neumann at the time)

I have a Horch RM2 which uses the AC701k.
From outside the Horch looks like an U47.

Not that I think it's a good idea to use a tube that is no longer in poduction and still in use in so many vintage mics, which raises the price for the tube.

Kai Schluenz


Wow, shows how little I know.  I had no idea that there were LDCs out there that used the AC701.

Certainly the M49 is a studio classic, but I am left wondering about the sound of these other AC701-based LDCs.  Do they have the smoothness of the SDCs that employ the AC701?  Does the AC701 empart the same tonal characteristics onto the LDC's capsule?

Unfortunately the M49 is WAY out of my price range.  Maybe though some of these others represent bargains to be had?  Now my interest is piqued; I would be very interested in trying one of these out.  Where should I start?

Thanks guys!
-Terrence Town


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