AKG D20, D25

https://www.akg.com/on/demandware.static/-/Sites-masterCatalog_Harman/default/dwbb53d52e/pdfs/D25.pdf

AKG C12

https://www.akg.com/on/demandware.static/-/Sites-masterCatalog_Harman/default/dwfb1506c7/pdfs/C12.pdf


Schematic:
https://www.elektroakustika.cz/akgc12.html


Information on CK-12 capsule
http://www.saturn-sound.com/Curio's/akg's_ck12_capsule.htm

AKG circuit for 6072 electron tube low noise selection tests

Cathode resitor 2K7 in parallel with 33μF.


Grid to ground resistor 200MΩ in parallel with 200pF.


Anode resistor 100K (this should be a low noise one?).


1μF capacitor from anode to primary of a 10:1 output transformer. Other side of primary to ground. Secondary is connected to to a 60dB amplifier. (A psophometer should be great too?). Then there is a Sennheiser UPM550 filter.


The cathode of the other triode section is shown connected to ground.


Ug max 3.8mV eff.
A weighted Ug Max 2.5mVeff, 1.9mV eff normal?

Psophometers are equipment for measuring electrical noise

Measuring thermal motion of electrons ie hiss.


Great examples should be by Rohde and Swartz, Siemens, Bruel and Kjaer, Hewlett Packard,...

More information on AKG C12 condenser microphone

Includes a photo including the designer Conrad Wolf:
http://www.micshop.com/AKG_History.pdf

Pinewood Studios

Linwood Studios - Oxford Digital Media YouTube channel
https://m.youtube.com/watch?v=MHQ1QfpLzvE

History of AKG

http://www.micshop.com/AKG_History.pdf