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 worked on 4 SM204s and they all had shallow resonator CK12 capsules which were manufactured in the middle 1950s