Hi All,

[33marsden]

I had a akg c12 vr mic without psu. I am seeking help if I could do some mods to make a psu of akg p820 to work with the c12 vr mic. The c12 vr mic has a 9 pin plug and from its schematic diagram, it seems it only uses 6 pins from the psu. I have some practical skill to solder things together and a bare basic understandibg of electronics. Hope someone would give some direction.

Thanks,

 

[LevinGuitar]

Here you can find both schematics
https://groupdiy.com/threads/akg.44737/

 

[Accelerator]

@33marsden​

I had a akg c12 vr mic without psu. I am seeking help if I could do some mods to make a psu of akg p820 to work with the c12 vr mic. The c12 vr mic has a 9 pin plug and from its schematic diagram, it seems it only uses 6 pins from the psu. I have some practical skill to solder things together and a bare basic understandibg of electronics. Hope someone would give some direction.

Thanks,

Hi 33marsden, greetings from Greece and welcome aboard!...

I attach the Service Manuals for the AKG C-12 VR and the AKG Perception 820 Tube Microphone, but more “apocalyptic” it is the attached Schematic of the AKG Perception 820 Tube Microphone…

The AKG C-12 VR runs up the 6072 – 12AY7 valve at the very typical “ol’ school” AKG’s HT of 120 DC Volts as Vb, but as you can see the AKG Perception 820 Tube Microphone like its predecessor the AKG Solidtube Microphone runs up the ECC83 – 12AX7 valve at the pretty high "modern" HT of 205 DC Volts as Vb, so actually you will got 195 DC Volts at the plates…

So, if you plan to modified the AKG Perception 820 Tube Microphone P.S.U. to work with the AKG C-12 VR Microphone, you will have a wholla lotsa of work to stepped down the HT at the 120 DC Volts…

 

[33marsden]

Thanks Accelerator. This is great help. So not much hope given my limited knowledge of components. I also have a psu of Rode NKT which uses 6922 tube and sound fine to me. Is it suitable ? I realise it has no pattern variations only cardiod.
Thanks again

 

[gyraf]

The 6072 (12AY7) is probably the only of these tubes that is really suitable for a microphone. Yes, you can often get the others to work, but with huge variations in quality and predictability

 

[33marsden]

Thanks Gyraf for your input. I think i need to gain basic knowledge as to how a psu of a tube mic work before anything should be committed as I paid quite a bit $ for this mic- better to be safe.

 

[33marsden]

Thanks everyone for responding to my post. after browsing a bit, i guess i understand that a tube needs two dc voltages supplied to it to make it work in an amp - one connected to its plate and the other " heater" to warm the tube . In the case of AKG c12 vr mic, the tube plate needs +120dcv and the heater needs +12.6dcv.

I have bought a Chinese tube psu and carried out some tests.

Results

Pin 1 +117.6dcv
Pin 2 +6 to 7 adjustable inside the chasis
pin 3 ( referred to as pointing adjustments from 0.0 to 100dcv depending on positions on the adjustment pot, I think this is pattern selection)
I think I can use Pin 1 117.6v to power the mic's plate ( akg schematic want 120v). Photos of this psu enclosed with its schematic diagram)

Now the heater requires 12.6v which is not readily avaliable in this psu. So I intend to use an external psu with 12.6dcv specs. What I need help is how to connect this 12.6v external psu to the heater pin. I undetstand that + terminal to that + pin as stated in akg's schematic but the - terminal of this external psu to ground ? I guess there is an external circuit created for supplying the 12.6v here. So to complete a circuit the - terminal must be connected somewhere. I hope someone would help.

Thanks,

 

[Accelerator]

@33marsden​

Thanks everyone for responding to my post. after browsing a bit, i guess i understand that a tube needs two dc voltages supplied to it to make it work in an amp - one connected to its plate and the other " heater" to warm the tube . In the case of AKG c12 vr mic, the tube plate needs +120dcv and the heater needs +12.6dcv.

I have bought a Chinese tube psu and carried out some tests.

Results

Pin 1 +117.6dcv
Pin 2 +6 to 7 adjustable inside the chasis
pin 3 ( referred to as pointing adjustments from 0.0 to 100dcv depending on positions on the adjustment pot, I think this is pattern selection)
I think I can use Pin 1 117.6v to power the mic's plate ( akg schematic want 120v). Photos of this psu enclosed with its schematic diagram)

Now the heater requires 12.6v which is not readily avaliable in this psu. So I intend to use an external psu with 12.6dcv specs. What I need help is how to connect this 12.6v external psu to the heater pin. I undetstand that + terminal to that + pin as stated in akg's schematic but the - terminal of this external psu to ground ? I guess there is an external circuit created for supplying the 12.6v here. So to complete a circuit the - terminal must be connected somewhere. I hope someone would help.

Thanks,

You only need to modified the Heater Topology in your AKG C-12 VR microphone from 12,6 DC Volts to 6,3 DC Volts, so in simple and plain words you connect the 4 & 5 pins together to one pole, you connect the 9 pin to the other pole et voila you have transform the series 12,6 DC Volts connection that the AKG C-12 VR microphone has to en parallèle 6,3 DC Volts Connection and you can work now your AKG C-12 VR microphone with your Chinese P.S.U.

See the attached photo about Vacuum Tubes Heater Topology – 12.6 DC Volts ~ 6.3 DC Volts

 

[33marsden]

Thanks Accelerator for your super quick help. I will try it out as per your advice.

Cheers,