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Author Topic: Akg c28c restoration  (Read 229 times)

Offline John diggs

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Akg c28c restoration
« on: August 07, 2018, 11:21:27 am »

Hi, i need the advice of more experienced people.

I acquired a pair of vintage akg c28-c (the nuvistor version).

They came from a guy who bought a broadcast lot a long time ago. They came without psu and connectors, they haven't been used in probably 20 years.

I had Leo Schall build me a psu and machined connectors
(Very well made!).

I have not tested them yet for fear of damaging critical components (like the transformer).

Is there any component i should test before applying power?  Critical resistors? Capacitors?  The 25uf cap is tantalum.


Offline klaus

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Re: Akg c28c restoration
« Reply #1 on: August 07, 2018, 01:10:49 pm »
Damage to the Nuvistor is probably your biggest concern when starting up a new supply.

I would therefore

1. confirm pin-outs of supply and mic, and make sure heater voltage comes in on pin 4 of the mic connector

2. I would stick a volt meter between pins 10 and 12 of the tube (heater and ground) and, as I turn on the supply, observe that the voltage does not rise beyond 5VDC. which is the prescribed heater voltage for that Nuvistor in that mic.
« Last Edit: August 07, 2018, 01:27:02 pm by klaus »
Klaus Heyne
German Masterworks®