Official C12 Clone - Build and Support Thread

[Hotsen]

Hi guys,
I got some trouble:
In the final step, (with the mic plugged) I already got a 6.30V heater, but I cannot raise down B+ less than 150V (min trim) and bias less than +2,3V.
All the steps where good before this final one...

I got an electro harmonix 6072a/12ay7 tube
An ami T14 transformator
An Rk12 capsule
The v1.1a revision
And a 1uf c12 cap in the mic

I am from france, so my power supply is configured on 230v!
So did I need to got the same values than u?

Best
Jeremy

If all parts of the circuit are functioning properly, increase the value of the R1, R2 resistors to drop the B+ voltage.

Hi Chunger!
Thx for your answer!
A last question:
I am european, had the values needed on B+ and Bias still 120V and -1V?

Sorry I am pretty newbie...

Cheers

 

[andybaker28]

Hi there,

I just finished my build and started checking voltages and have found my transformer seems to be producing 200V ok, but the 9.5 side appears dead. It was working earlier on the transformer but I was never getting heater voltage at P8. Anyone ever have one of these die? And or any thoughts on what might have caused it to die? I had no smoke or hot fire ashes anywhere along the way!

 

[Matador]

Hi there,

I just finished my build and started checking voltages and have found my transformer seems to be producing 200V ok, but the 9.5 side appears dead. It was working earlier on the transformer but I was never getting heater voltage at P8. Anyone ever have one of these die? And or any thoughts on what might have caused it to die? I had no smoke or hot fire ashes anywhere along the way!

When it's completely disconnected from the board, you measure nothing across the secondary winding when powered?

 

[andybaker28]

Hi there!

Thanks for the reply. Well I have dug a bit further into it now and found that the transformer contrary to what I thought before it is working on the primary and secondary. The primary is reading around 220V and the secondary 10V when disconnected. I must have a mistake somewhere but I cannot find anything yet, When I measure on the block shown on the build guide I am getting more than 300V! When I adjust the variable pot the lowest I can get is 246V. As for the Bias and heater I am not getting any measurement at all on P8 or P4. Not sure what I have done wrong! I was trying to just use the original switch but realized on the V1.4 board the ground is in a different spot that the build guide. I just took the polar switch out of the circuit but still getting the same results so far..  If you have any ideas I would appreciate it!

Thanks!

Andy

Hi there,

I just finished my build and started checking voltages and have found my transformer seems to be producing 200V ok, but the 9.5 side appears dead. It was working earlier on the transformer but I was never getting heater voltage at P8. Anyone ever have one of these die? And or any thoughts on what might have caused it to die? I had no smoke or hot fire ashes anywhere along the way!

When it's completely disconnected from the board, you measure nothing across the secondary winding when powered?

 

[Matador]

Hi there!

Thanks for the reply. Well I have dug a bit further into it now and found that the transformer contrary to what I thought before it is working on the primary and secondary. The primary is reading around 220V and the secondary 10V when disconnected. I must have a mistake somewhere but I cannot find anything yet, When I measure on the block shown on the build guide I am getting more than 300V! When I adjust the variable pot the lowest I can get is 246V. As for the Bias and heater I am not getting any measurement at all on P8 or P4. Not sure what I have done wrong! I was trying to just use the original switch but realized on the V1.4 board the ground is in a different spot that the build guide. I just took the polar switch out of the circuit but still getting the same results so far..  If you have any ideas I would appreciate it!

Thanks!

Andy

A few things:
1) Make sure you measure with a test load.  A good test load is a 170K (0.5W) resistor inserted into the jack between B+ and ground.
2) I don't see a jumper for the heater- line.  You need to ground it if you are using positive heaters.

http://groupdiy.com/index.php?topic=51377.msg760350#msg760350

 

[andybaker28]

Thanks Chunger!

That got my power supply sorted and I was able to set all the voltages now. At first I was not sure what else I did wrong,  I was not getting a  good signal out of the rear capsule. It was working, but the output was pretty low and very muffled.  I was able to figure it out, the rear backplate was not getting good connection on capsule. The screws were too short is my guess cause it worked fine after installing longer ones, its up and running good and quiet now! Still pretty new to DIYing but I have finished two mics now and it will continue to get easier as I learn more.  Looking forward to  M49 and U47 clones next…

Thanks much!

Hi there!

Thanks for the reply. Well I have dug a bit further into it now and found that the transformer contrary to what I thought before it is working on the primary and secondary. The primary is reading around 220V and the secondary 10V when disconnected. I must have a mistake somewhere but I cannot find anything yet, When I measure on the block shown on the build guide I am getting more than 300V! When I adjust the variable pot the lowest I can get is 246V. As for the Bias and heater I am not getting any measurement at all on P8 or P4. Not sure what I have done wrong! I was trying to just use the original switch but realized on the V1.4 board the ground is in a different spot that the build guide. I just took the polar switch out of the circuit but still getting the same results so far..  If you have any ideas I would appreciate it!

Thanks!

Andy

A few things:
1) Make sure you measure with a test load.  A good test load is a 170K (0.5W) resistor inserted into the jack between B+ and ground.
2) I don't see a jumper for the heater- line.  You need to ground it if you are using positive heaters.

http://groupdiy.com/index.php?topic=51377.msg760350#msg760350

 

[Andriejus]

Hey,

I have finally finished my C12 mic using Chunger's mic body. All voltages are OK and the mic sounds good, but I have hum in the audio. This thing disappears when I cover the headbasket with brass mesh, or touch the headbasket with full hand.

I found that I am using wrong tube - 12AT7. Might this be a problem? Anyone has experienced this? Maybe problems with headbasket?

Kind regards,
Andrew

 

[micaddict]

I found that I am using wrong tube - 12AT7. Might this be a problem?

12AT7 is a fine tube and it's easier to find good ones than to find good 12AY7/6072a tubes.

In this very thread, Matador describes some minor component changes to best suit the 12AT7.

 

[micaddict]

Replies #872 and #874.

In short:

12AT7 Conversion - Summary

Microphone:  Change R17 from 100K down to 47K
PSU:  Drop R1 and R2 down to 33K.  Adjust R3 down to about 900ohms, then tweak with the actual tube.
Test load: decreases from 180K down to (120V/1.35mA) = 88K.  91K would work as a substitute for a real tube for PSU testing.

 

[ViciusbeatZ]

Hi family!!

Is this project available for the t.bone SCT 800?

 

[ln76d]

Truly i don't know is it minions microphone fit SCT 800 but you can make C12 circuit inside SCT800 without any problem.
It's just a swap of few components on pcb.
But if you need bananna pcb try it.
Thomann also sell multipattern power supply which can be converted to this project.
If you want i have good schematic of sct800 modification - something between ELAM and U47

 

[ViciusbeatZ]

OK thanks!
and where I can find information on the modification of SCT800 because I can not find it anywhere , neither here in groupdiy

 

[ln76d]

OK thanks!
and where I can find information on the modification of SCT800 because I can not find it anywhere , neither here in groupdiy

I don't know is it any
If i will have more time i can make it.
It's relly simple.
Send me reminder on a days and i will make post with schematic refering  to part numbers on SCT800 PCB.
Original PCB  should fit all needed components.

Do you need multipattern or cardioid only is enough?

 

[ViciusbeatZ]

Au thank you cardioid is enough, and but also I would like to see the differences MultiPattern for future

 

[ln76d]

For you:

http://groupdiy.com/index.php?topic=62661.0

 

[Andriejus]

Hey,

I have finally finished my C12 mic using Chunger's mic body. All voltages are OK and the mic sounds good, but I have hum in the audio. This thing disappears when I cover the headbasket with brass mesh, or touch the headbasket with full hand.

I found that I am using wrong tube - 12AT7. Might this be a problem? Anyone has experienced this? Maybe problems with headbasket?

Kind regards,
Andrew

Hey All,

Solved my problem by adding additional layer of wire mesh inside the headgrille..

Kind regards,
Andrew

 

[DDay]

Hi, I was wondering if You're likely to get the C12 parts kit available again soon Chunger? Or if anyone has a recommendation for buying the parts in the UK / Europe I'd be very appreciative.... Just to clarify I only need the components (for the power supply and mic), I have the body etc.

 

[ln76d]

What's the problem to make it point to point? Acrylic? Rest is nothing - few resistors and caps.
Want c12 - buy vintage parts - ebay here's best option.

 

[DDay]

Thanks, I have the pcbs. Just unsure which components need to be 'special' ( caps in audio path? ) and which can be standard..

 

[ln76d]

There's not much in audio path - two capacitors.
1nF at the input (styroflex/polystyrene) 500nF at the output (MP - metal paper) - you want both type as original - believe me
Don't ue MKP/polypropylene at the output!
http://www.filmsoundsweden.se/voxbilder/filmhist/akg-c12-schema1.jpg