R/E/P Community
R/E/P => Klaus Heyne's Mic Lab => Topic started by: John diggs on August 07, 2018, 11:21:27 AM
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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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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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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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How would you know its a 'c' version displayed in the video?
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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.