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Author Topic: Akg c28c restoration  (Read 359 times)

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.


Thanks
John
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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.
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Klaus Heyne
German Masterworks®
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Timjag

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Re: Akg c28c restoration
« Reply #2 on: October 14, 2018, 05:41:45 pm »

I was just thinking of asking you about that klaus. Was there a reason that AKG used 5 volts for the 7586 tube? It quite clear on every data sheet I’ve seen that it’s requires a regular 6.3v 135mA supply. Was it a heat issue, being inside a metal tube and not wanting to burn David Bowie’s hand on totp  or something?(joke!)

Here he is doing the magic with one!

https://m.youtube.com/watch?v=yEmGQYCuc6M


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klaus

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Re: Akg c28c restoration
« Reply #3 on: Yesterday at 12:58:48 am »

How would you know its a 'c' version displayed in the video?
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Timjag

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Re: Akg c28c restoration
« Reply #4 on: Yesterday at 07:01:03 am »

I wouldn’t! I was being silly, I guess the humour was lost in text. I did buy 4 that were ex-BBC 2 of which were Cs and two As. From what I heard they bought a lot.
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