AKG C12/C28A output transformer wiring T14/1 any info......

gary o · Aug 30, 2011

Hi has anyone got wiring info for the original T14/1 please.........

Ive been using a T14/1 from a AKG C28A in a DIY mic A Studio Projects TB1 ...Iv just done a quick point to point copy.....sadly one of the wires of the T14 has come off........

I have another C28A to look at but Im getting a bit confused about the wiring of it, it looks to me like one of the wires goes to the HT that cant be right......

I can take some pics....if needed

thanks for reading......

gary o · Aug 30, 2011

http://www.jlmaudio.com/C28A%20circuit.gif

Answering my own questions a little its seems the T14 in the C28A doesnt go to ground & kinda does go to the B+..........& theres a 100K resistor across the primary winding and output cap.....and the 2 500K voltage divider hanging on B+ too

So does the T14 primary have to pass any B+.......I guess not because it has nowhere to go ? it that right ?

MagnetoSound · Aug 30, 2011

gary o said:
So does the T14 primary have to pass any B+.......I guess not because it has nowhere to go ? it that right ?

Correct. DC is blocked by the cap. B+ arrives at the plate via the 100k.

Interesting, isn't it. Consider the fact that the B+ rail is filtered to ground by the last cap across the RC string in the HT supply, and you can see that, as far as AC is concerned, the transformer doesn't care whether ground is hot or cold.

gary o · Aug 30, 2011

Thanks Dan its very interesting I thought I was going mad when I was tracing the wiring my C28A......I think I understand whats going on well partly.....I was looking at C12 schematic at the time & couldnt find earth on the primary, I had read the C28A is same circuit as C12 but its not looking at my C28A schematic now .....I also read the C28A has lower noise......interesting stuff I wish I understood better.....Iv just added the T14/1 to the studio projects TB1 which seems like the C12 schematic......

big thanks....

AKG C12/C28A output transformer wiring T14/1 any info......

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gary o

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