AKG C12 A / B Version Build

[Spencerleehorton]

Just seen this version which would be better 9.5:1.

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F111683319855

Or even this? 12:1?

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F111540701945

 

[Vac11]

Here is C12A transformer feeler thread. Join to us, if you are interested in Moby's U11 transformer suitable for this cathode follower circuit....

https://groupdiy.com/index.php?topic=76131.0

 

[Spencerleehorton]

having another look at these C12a and the pattern selector seems to work fine and produce correct voltages sent on pin 3 on mic socket but i dont seem to hear any difference in pattern form?
I built 2 mics and both are the same?

there is also a slight hum when i turn up the gain which is weird, B+ is 116v and H+ is 5.2v

Ive checked my connections and all seems correct, Im assuming it should be a step down transformer as thats how i have it wired?
and also the capsule im assuming has single backplate as thats what i have?

chassis gnd on XLR socket isnt connected only chassis gnd connected to diode bridge negative on B+
pin 1 on XLR socket goes to gnd.

 

[Spencerleehorton]

the hum is there when i plug the mic in and goes away a fair bit once tube fires up but i can still hear the hum in the back ground and its annoying!!
Im wondering whether it could be the toroidals being too close to the pcb?