Official C12 Clone - Build and Support Thread

[rock soderstrom]

Thanks a lot for info
First Im going to use it for a C12 steropair but also thinking about the possibility
to use this psu for a D-EF47 with B+ 105V and H+ to 5.05V
Should that be possible?
Anyone tried it?

This will somehow work with heavy mods to the existing PCB. You will have to replace the LM7806 with a 7805, throw out the diode that elevates it and add more RC filtering for F+, as this will bias the cathode. Then adjust B+ with the series resistors (Zener diodes too) and it should work. I would probably choose a different design though...



I just did something similar with a SCT800 power supply, since it has too little B+ filtering, I replaced the Zener diodes with another 33uF capacitor, which forms an additional RC filter with this resistor.

 

[Nick6691]

This will somehow work with heavy mods to the existing PCB. You will have to replace the LM7806 with a 7805, throw out the diode that elevates it and add more RC filtering for F+, as this will bias the cathode. Then adjust B+ with the series resistors (Zener diodes too) and it should work. I would probably choose a different design though...

View attachment 136872

I just did something similar with a SCT800 power supply, since it has too little B+ filtering, I replaced the Zener diodes with another 33uF capacitor, which forms an additional RC filter with this resistor.

Thanks for input Rock,
After the C-12s (D-12) I´m about to build Danys D-EF47 and would really like to build the power supply that comes with that pcb kit.
But I´m not able to find a build guide for the psu, only for the microphone. (For the D-47 there is an excellent guide)
I dont have the skills to do it without a guide. Do you know if there is one? Have searched tho forum for days.
Maybe this discussion ended up in the wrong thread.

Nick

 

[Accelerator]

It seems 12AY7 was at least registered at 1948.

https://www.radiomuseum.org/tubes/tube_12ay7.html

It “seems” means nothing without any Official Tube Datasheets from the Big 4 Tube American Companies (General Electric, RCA, Tung-Sol, Western Electric Co. – Westinghouse)

I will not disagree with you that back in time maybe some very minor smaller tube company like the American Arcturus Radio Tube Company or the Australian AWV or the American Chatham Electronics Corporation or the American Rogers Majestic Electronics Ltd. may had registered the 12AY7 tube back at 1948 and sells them at small quantities, but when we are talking about American tubes mainly the most of us we are talking about the mass production of American tubes by the Big 4 Tube American Companies (General Electric, RCA, Tung-Sol, Western Electric Co. – Westinghouse)

I'm not trying to argue that the 12AT7 can't be used in a microphone—I've used it myself—but I'm just wondering where your information about its usage in the C12 comes from. I've never heard of that before.

The AKG C-12 Microphone system was the most expensive microphone system back in time at 1954, with a price range at $1.450 U.S.D. something very equal to $8.000 U.S.D. in today’s price range analogy and back in time they weren’t bedroom studios with DAWs, individual customers, so it is very logical for all of those Big American Studios to demanded from the Austrian “Boutique Newcomer” to have these AKG C-12 Microphone System(s) with the (all) American and common 6072A – 12AY7 tube…

As you can see by the attached file, there wasn’t any AKG C-12 Microphone System Schematic with the (all) American 6072A – 12AY7 tube before 1959 and from the other hand we have got today all of this “Ol’ wife’s tale” of biasing at -1Volts and the 2K7 Cathode Resistors in the AKG C-24 microphone system as clear indicators of using the ECC81 – 12AT7 tube…

 

[pasarski]

It “seems” means nothing without any Official Tube Datasheets from the Big 4 Tube American Companies (General Electric, RCA, Tung-Sol, Western Electric Co. – Westinghouse)

I will not disagree with you that back in time maybe some very minor smaller tube company like the American Arcturus Radio Tube Company or the Australian AWV or the American Chatham Electronics Corporation or the American Rogers Majestic Electronics Ltd. may had registered the 12AY7 tube back at 1948 and sells them at small quantities, but when we are talking about American tubes mainly the most of us we are talking about the mass production of American tubes by the Big 4 Tube American Companies (General Electric, RCA, Tung-Sol, Western Electric Co. – Westinghouse)

The AKG C-12 Microphone system was the most expensive microphone system back in time at 1954, with a price range at $1.450 U.S.D. something very equal to $8.000 U.S.D. in today’s price range analogy and back in time they weren’t bedroom studios with DAWs, individual customers, so it is very logical for all of those Big American Studios to demanded from the Austrian “Boutique Newcomer” to have these AKG C-12 Microphone System(s) with the (all) American and common 6072A – 12AY7 tube…

As you can see by the attached file, there wasn’t any AKG C-12 Microphone System Schematic with the (all) American 6072A – 12AY7 tube before 1959 and from the other hand we have got today all of this “Ol’ wife’s tale” of biasing at -1Volts and the 2K7 Cathode Resistors in the AKG C-24 microphone system as clear indicators of using the ECC81 – 12AT7 tube…

Here's a RCA datasheet from 1954
https://www.google.com/url?sa=t&sou...IQFnoECBEQAQ&usg=AOvVaw0hYOdAp7h2DXfeUNlvVx8q

 

[Tim Campbell]

Accelerator I have data sheets dating 1955 from GE and I am sure there are older. The first 100 C12s were actually branded Seimens SM204 and every one I have seen had a GE 6072 in it(though they could easily have been changed). I have never seen an old one with an original Tung Sol. Have you seen any C12 schematics beyond the C1 specifying another tube?
RCA developed the 12ax7 in 1946.

 

[Accelerator]

Here's a RCA datasheet from 1954
https://www.google.com/url?sa=t&sou...IQFnoECBEQAQ&usg=AOvVaw0hYOdAp7h2DXfeUNlvVx8q

This is the Tube Datasheet of RCA 12AT7 1954 – Not the Tube Datasheet of 12AY7, Neither the Tube Datasheet of 6072A …

 

[Tim Campbell]

Here is a GE from 1954 but I have seen a Tung Sol sheet from 1951: The date is at the bottom of page 2.
The SM204 was built in 1954.

 

[Accelerator]

@Tim Campbell​

Accelerator I have data sheets dating 1955 from GE and I am sure there are older. The first 100 C12s were actually branded Seimens SM204 and every one I have seen had a GE 6072 in it(though they could easily have been changed). I have never seen an old one with an original Tung Sol. Have you seen any C12 schematics beyond the C1 specifying another tube?
RCA developed the 12ax7 in 1946.

Tim with all of my during respect that I have to you, I have to inform you that the AKG - Siemens 204 tube microphone was a total different microphone that the AKG C-12 Microphone System, as the AKG - Siemens 204 tube microphone was Cathode Biased by 1k8 Cathode resistor while the AKG C-12 Microphone System has Fixed-adjustable bias, and the most important is that the AKG - Siemens 204 tube microphone was produced back at the 1960, not at the 1953 like the AKG C-12 Microphone System…

 

[pasarski]

This is the Tube Datasheet of RCA 12AT7 1954 – Not the Tube Datasheet of 12AY7, Neither the Tube Datasheet of 6072A …

Sorry I meant to link this. This is a 12AY7 datasheet from 1953. So it definitely existed before 1956.
https://www.google.com/url?sa=t&sou...gQFnoECBQQAQ&usg=AOvVaw0I4xREpA_eZBFrDZSeFLwl

 

[rock soderstrom]

Do you know if there is one?

No, sorry.

 

[Tim Campbell]

Accelerator I don't want to disagree with you but I just got off the phone with 2 of the old engineers at AKG who checked their records and verified to me that the original SM204 was produced in 1951 and changed slightly over a couple of years until the final version SM204/23 was produced in 1953. I only have this by phone but I can try to get them to send me copies. I have no idea why your schematic is stamp dated 1960. I have worked on 4 SM204s and they all had shallow resonator CK12 capsules which were manufactured in the middle 1950s. I understand the biasing differences but the greatest difference is the transformer. Supposedly there were some manufactured with a Henry transformer but those I have seen had Rode and Schwarz.

I am not sure I would call these completely different microphones but there are differences.

Actually the photo you posted of the pair of SM204/23 internals is a photo that I took

 

[Accelerator]

@Tim Campbell​

Accelerator I don't want to disagree with you but I just got off the phone with 2 of the old engineers at AKG who checked their records and verified to me that the original SM204 was produced in 1951 and changed slightly over a couple of years until the final version SM204/23 was produced in 1953. I only have this by phone but I can try to get them to send me copies. I have no idea why your schematic is stamp dated 1960. I have worked on 4 SM204s and they all had shallow resonator CK12 capsules which were manufactured in the middle 1950s. I understand the biasing differences but the greatest difference is the transformer. Supposedly there were some manufactured with a Henry transformer but those I have seen had Rode and Schwarz.

I am not sure I would call these completely different microphones but there are differences.

Actually the photo you posted of the pair of SM204/23 internals is a photo that I took

Tim, I totally agree with you that the transition from the AKG flat-shallow dish resonator CK12 capsules which were manufactured in the middle 1950s to the AKG deep dish resonator CK12 capsules at the early 1960’s and the transition from the Henry V-3044 transformer to the Henry V-2148 Transformer (AKG C-12 Microphone System at middle 1950s) and then to the Rohde & Schwarz V-2545 (AKG C-12 Microphone System at late 1950s, AKG - Siemens SM203/4 - C23 Tube Microphone at late 1950s/ early 1960’s) to the Haufe T14-1 (AKG C-12 Microphone System at early 1960s, AKG C-24 Microphone System at early 1960s, AKG-Telefunken ELA-M 250/251 (non E with the AC701K tube) and AKG-Telefunken ELA-M 251E (with the 6072A tube) were the “huuugeeee steps” in the transformation to what we all know today as “AKG C-12 sound-like”...

AKG was the small Austrian “newcomer boutique” company back in time at middle 1950s with non the “big history and the clear records” neither the “Big Status” that both Neumann & Schoeps had, so they had to did everything just to “make their fit” in the antagonistic microphones market, and logically there were several “back and forth” decisions about their microphones

So, as we can see today that they used the AKG flat-shallow dish resonator CK12 capsules which were manufactured in the middle 1950s anachronistically in the AKG C-414 EB microphone at 1976, they keep as "urban legeng" the uncorrected “Ol’ wife’s tale” value of biasing the 6072A tube at Grid Bias Voltage (V) -1 Volts for the AKG C-12 Microphone System and the uncorrected value of 2k7 Cathode Resistors at C-24 Microphone System with the 6072A tube which are clear indicators of a previous one designing and implementation of C-12 / C-24 microphone system(s) running at 120 DC Volts Vb with the ECC81 – 12AT7 valve, as the correct values for the 6072A – 12AY7 tube running at 120 DC Volts Vb is Grid Bias Voltage -1.23 Volts for the AKG C-12 microphone system and the correct values are 2K05 Cathode Resistors for the C-24 microphone system(s)…

The only “Unofficial” report that I have for the usage of 6072A - 12AY7 tube in the AKG C-12 Microphone System comes from the American magazine “Electronic Design News” and it was dated at April 1957…

Before this from 1953 to 1957 there was nothing in the Official and Unofficial record about the tubes for the AKG C-12 Microphone System…

Returning to the topic as Matador has involve both of these options of the usage of ECC81 – 12AT7 valve with 47KΩ Anode Resistor at 120 DC Volts Vb I can say that the correct Grid Bias Voltage (V) is -1.01 Volts and if someone would like to use the 6072A - 12AY7 tube with 100KΩ Anode Resistor at 120 DC Volts Vb the correct Grid Bias Voltage (V) is -1.23 Volts…

 

[Tim Campbell]

https://groupdiy.com/threads/akg-c12-siemens-sm204-help-needed.62801/post-796425

In an old thread about the SM204/23

 

[Accelerator]

@Tim Campbell​

https://groupdiy.com/threads/akg-c12-siemens-sm204-help-needed.62801/post-796425

In an old thread about the SM204/23

Wow, just Wow Tim!..

What a very nice thread about the AKG C12 / Siemens SM204 was that?...

It seems that back in time all of you old “good fellas” you lived it up here in the microphone section with all of those legendary and expensive tube microphones, unlike the today’s cheapie, cheapie FET days…

I know that we may “Hi-jacked” a little bit the Matador ‘s Official C12 Clone - Build and Support Thread about the AKG – Siemens SM-204 microphone and I have forward to say sorry to him about that, but there is a very interesting info (or speculation…) about the AKG – Siemens SM-204 microphone, that unlike the AKG C-12 Microphone System which used 250MΩ Resistors (at R14 - R15) the AKG – Siemens SM-204 microphone it had 100MΩ Resistors (at R14 - R15) something quite “close” to the 60MΩ Grid-leak Resistor that the Neumann used for the Neumann U-47 microphone and for this reason (plus the AKG flat-shallow dish resonator CK12 capsules which were manufactured in the middle 1950s & the Rohde & Schwarz V-2545 transformer) the AKG – Siemens SM-204 microphone sounds like a “transition between” the AKG C-12 Microphone System & the Neumann U-47 microphone…

Oliver Archut (RIP) points it with the 100MΩ Resistors (at R1 - R5) to his Oliver Archut C12 Alternative Schematic Updated-Alina schematic…

 

[k4343011]

Thanks to many people here, I was able to DIY my c12.
Thank you to everyone here.
I used Beesneez's ck12 capsule, cinemag's transformer, and GE 6072 tube.

 

[tonycamp]

Hello,
I did change all polystyrene today.
Still the same issue unfortunately.
I can have b+ at 120v with a 180k strapped between b+ and ground, but when I plug the mic, voltage is rising past 120 and more...
I changed the tube, same problem.
Any idea what could it be?
Thanks a lot

hey, sorry i took this long, the good news is your PSU is behaving as it should unplugged, i'd check continuity on all you're mic cable leads(don't forget the barrel) to make sure you aren't bleeding off somewhere, and can you post up some very clear pictures of all aspects of your mic build, i'm not sure what is going on but i might see something you're missing

 

[daschnoz]

Fraternal Twins



Apex 460 donors
The green one is almost the complete Mini-Mod.

• 62V zener swap
• NOS RCA 12AT7
• 220pF cap across pins 1 & 9
• stock capsule
• stock x-fmr
• stock input cap (it's polyester, and I would have changed it to that anyway if it wasn't)

---

The purple one is the C12 board/parts kit from chunger.

This stuff drives me crazy. While checking the mic on the bench, I couldn't figure out why my polarizing voltages were WAY lower than they should be. Everything looked good until I tried to get a voltage on "the other side" of the resistors. I had 2.6V on the back plate and 30V on the rear diaphragm (110V input). I was at the point where I would start doing stupid things, so at midnight, I shut it down.

This morning it occurred to me.... I've never worked with resistor values this high before. I wonder... So I pulled the spec sheet for my multi-meter (Fluke 115), and wouldn't you know it, the input Z on it is spec'd at " >10M". So doing the math using the 10M input of my meter as the "other" resistor in the voltage divider...
10M / 260M = 0.038
0.038 * 60V = 2.3V - (measured 2.6 on the back plate, close enough)

10M / 40M = 0.25
0.25 * 110V = 28V - (measured 30V on the rear diaphragm, again, close enough)

So yup, the meter was indeed acting as the "other" resistor in the voltage divider.

Voltages around the tube are perfect, so I figured why not... there's nothing to blow up here. So I plugged it in, turned it on, and WOW!!! It works!!!

I don't know if this has been mentioned in the 150+ pages of this thread that proceed this, but don't forget about the input impedance of your meter. Most of the time it's high enough to stay out of the way. But here we are working with resistor values that are high enough where that input Z is actually low by comparison. If everything else checks out fine and you're still getting low voltage readings at these points, this may be why. Check the input specs on your meter, do the math. If your readings and the math are close, you're likely good.

ETA: Yeah, it's been mentioned before (I should use the search function more often). It occurred to me that instead of measuring to ground, measure across the resistors themselves. You should get zero volts (or something close enough to call it zero). If there's a short to ground or other bad connection, you'll have not zero.

As for the build itself:

• NOS RCA 6072
• stock x-fmr
• stock capsule (at the moment)
• stock resistor chain on the stock switch (it works, so I don't see the need to change it)

I did a quick spoken word recording with both. Being sent an identical signal from both mics, based on the visual EQ in my DAW, there is very little difference in the frequency response of the 2 mics. I can't wait to see how they compare when I put a better capsule in the C12.

 

[MicMaven]

Being sent an identical signal from both mics, based on the visual EQ in my DAW, there is very little difference in the frequency response of the 2 mics. I can't wait to see how they compare when I put a better capsule in the C12.

Quick Rookie Question - does this, perhaps, illustrate or demonstrate the proposition the capsule manifests 95% of the sound, while the circuit manifests the rest? (more or less) Or am I mixing my metaphors, as it were?

/ James

 

[daschnoz]

Quick Rookie Question - does this, perhaps, illustrate or demonstrate the proposition the capsule manifests 95% of the sound, while the circuit manifests the rest? (more or less) Or am I mixing my metaphors, as it were?

/ James

I was actually wondering the same thing. I did order a C12 capsule from Mic & Mod. We'll find out after I do the same test with the new capsule installed.

 

[MicMaven]

Thanks to many people here, I was able to DIY my c12.

Good Day Mr. @k4343011 -

I am sorry I did not even notice the microphone at all. I simply enjoyed the lovely music.

James