Official C12 Clone - Build and Support Thread

[Matador]

the red and Brown of the cinemag 13114  1.5k and yellow and orange 300ohm something like that David at cinemag said it was correct specs I wired red to ground and brown to TX correct? And yellow to 6 orange to 5 I swapped them as well  when I check the 1000pf cap to pin 7 on tube I don't get any reading that is supposed to be front capsule to grid correct? I'm using a multimeter all I got sadly

We ran into reversed transformers a few times:  I would measure the DC resistance of the primary and secondary and makes sure one pair is high (1K ish) and one pair is low (<50 ohms).

The cap connected to pin7 should go to the backplate(s), not the front capsule!  Please check the latest schematic on the first post (rev 4).

 

[Wilks978]

We ran into reversed transformers a few times:  I would measure the DC resistance of the primary and secondary and makes sure one pair is high (1K ish) and one pair is low (<50 ohms).

The cap connected to pin7 should go to the backplate(s), not the front capsule!  Please check the latest schematic on the first post (rev 4).

the build I'm working on it the ela m251 type I just haven't been getting responses on that forum so I messaged here, and I am wired correctly with the transformer I checked the readings pcb side 1.5k and 30ohms on pin 5 and 6 side to xlr... I'm not sure what's wrong

 

[Delta Sigma]

There's a lot of suspect looking solder joints in the photos you posted in another thread. Mostly, it's the turrets that look like they didn't flow well. There's a couple PCB pads that (TGND?) that also look like they didn't flow properly.

When you're soldering to turrets, it takes a lot of heat compared to the component. You should have a tip large enough to transfer heat to the turret (not too big though!). Heat the turrett first with a little solder bridge for heat transfer. Once the turrett is heated, add solder to the component. The solder should flow quickly. Use flux if needed, and clean it well after.

You could also, measure your B+ in your power supply, then measure in the mic. Measure at your plate, then the R3/R5 (not sure if resistor numbering the same on this project as Dany's 251). Take a measurement at your grid too. The voltage will measure waaay lower than it actually is but at least you'll know there's something there.

 

[Matador]

There really isn't enough information to go on to help further.

I would start with the schematics in the first post of the ELM 251 thread, as I had added measured voltages to many points, so I would confirm those on your mike are reasonably close to the schematic.

Other than that, you need a way to inject a test signal:  even a sound card can be used where you make up a plug on the output, load up a sine generator plugin, adjust it to 1V RMS, and inject it into various places in the circuit.

 

[funkymonksf]

I just received my Tim Campbell CT-12 capsule and I was surprised it wasn’t wired. Makes sense I suppose. Does anyone have a guide or advice on the best way to solder leads to the capsule? I’m using it for this very project.

Any guidance would be great.

 

[Delta Sigma]

I just received my Tim Campbell CT-12 capsule and I was surprised it wasn’t wired. Makes sense I suppose. Does anyone have a guide or advice on the best way to solder leads to the capsule? I’m using it for this very project.

Any guidance would be great.

Hmmm, no leads? Don't solder. I'm not even sure where to source the terminals. Every capsule I've purchased had leads attached or included with the little ring terminals already attached to the wires. Wait for Tim to chime in or you could contact him. He's a very frequent contributor to the forum.

 

[funkymonksf]

There are included terminal rings, but there's nothing idicating which is which. I see from the pics from Chunger that it "appears" the membranes (front & back) are soldered together on Tim's CK12 capsule. From the schematic I don't see why that'd be.

Does anyone have experience with Tim Cambell's CK12 capsule and how you wired it to this circuit?

 

[Delta Sigma]

Terminals were sent? Were four sent? Are the Front/rear diaphragms already terminated with leads but not the backplates?

Diaphragms are NOT connected together.

CK12 has isolated backplates. This allows for Elam 251 pattern switching. C12 connects the backplates to tube grid so the backplates must be connected together. Check out the schematic. Voltage divider puts 1/2 B+ on backplate. Front diaphragm is at 0V so this means for the rear diaphragm voltage: 0V=omni, 1/2 B+= Cardioid, B+= Fig8.

 

[Banzai]

There are included terminal rings, but there's nothing idicating which is which. I see from the pics from Chunger that it "appears" the membranes (front & back) are soldered together on Tim's CK12 capsule. From the schematic I don't see why that'd be.

Does anyone have experience with Tim Cambell's CK12 capsule and how you wired it to this circuit?

Front of CK12 is the side with 3 larger screws.
Rear has all uniform and evenly spaced screws.

Attach wires to front and rear solder tags. If building a C12 short the backplate tags together and attach a single wire.

 

[Tim Campbell]

Anyone who has bought one of my CT12 capsules knows that it comes with covers over the membranes clearly marked with one membrane as front and 4 tinned solder tags on the appropriate terminals. The 4 mounting screws are marked red.

It is also supplied with a diagram showing which terminals are what.

The covers should remain over the membranes during installation. Wires should be pre-tinned and the minimum amount heat and time should be used to attach the leads. After soldering the cables to the capsule the screws holding them should be checked to see if they remain snug/tight. The heat from solderiing them sometimes loosens the connection.

I am a little worried that anyone inexperienced enough to think that the membranes should be connected together may run into other problems with this build.

Perhaps there is someone  located close to you with more electronic experience that could help.

 

[jrasia]

Can someone tell me the length spacing between turrets on the microphone pcb?

I'm wondering how long of a resistor length I can use.  looks to be somewhere between 12mm - 16mm if I had to judge by the photos?

Might use some wirewound resistors for the build, but some can be pretty long in length.

Thanks

 

[funkymonksf]

Thank you all for your help. I'm a bit emberassed over my last question. However, I have another,

Which pinouts are supposed to be wired with the thicker gauge in the tube mic cable? I assume the heater wire is one of them. If so, what is the other? There are 5 x 26 gauge and 2 x 20 gauge wires in the Gotham cable I am using

.Thanks you for your time.

Pin 1 = B+. ?
Pin 2 = heater.    20g
Pin 3 = pattern ?
pin 4 = bias ?
pin 5 = audio -  26g
pin 6 = audio +  26g
pin 7 = ground 26g

 

[Matador]

You should use the thicker wires for heater power (the heater + connection), and audio 0V.  There isn't any appreciable current in any of the other wires to warrant moving to 20 gauge.

 

[JCraft]

I've run into a couple of issues with my build, one I've overcome, the 2nd I'm just digging into. 1st up was after completing my power supply I had no DC on the heater output, I had a full 9.5V of AC instead. After a lot of head scratching and a good nights sleep I determined that the heater section had no ground. Ground points were fine all over the board except the heater section so I ran a piece of wire on the backside of the board from the negative of C6 to a thru hole ground and  "Boom" I got a DC output at the heater terminal that adjusted to 6,3V like it was meant that way. Defective board? Not sure but it's working now.

2nd issue is my microphone board is silk screened "V1.4A Matador - 2018 C12 Microphone" purchased this past December and there are no terminals to hook up the capsule as shown at the beginning of the guide. I'm slowly figuring where to hook my Tim Campbell CT12 capsule to, but an explanation in the guide as to the changes and what to do would be very helpful since although I have built and wired several studios over the years this is my first venture into building a vacuum tube circuit. Since the date on the board is 2018 I've went back to mid-2017 in this thread looking for info on this without luck. Also I noticed I only received one board for the tube socket and the grids were not a thru hole soldier point but a 1/4" hole so I just soldiered the grey wire from "Grid" on the board to the grid pin on the tube socket, works for me if that's suitable.  Still looking thru the schematic and I'll ultimately get it, but help to a quicker solution would ease my mind.

Thanks in advance!

 

[JCraft]

I've kinda got this thing figured, need to know if I'm wrong. Looks like the front capsule connects to the junction of C11 & R16 which is silk screened RC on the board I have Whereis the post marked FC is a dead short to ground which is supposed to be the rear capsule according to the schematic. I know things happen so I'm not to stressed about it, just trying to make sure I'm correct before I attach a $400+ capsule and a NOS 1964 GE 5-Star 6072 (I've got  NOS 12AY7 from the late 60s in it for testing purposes).

Again thanks for any help in this ancient thread.

 

[Tim Campbell]

JCraft FC is front membrane and RC is rear membrane. The front membrane goest o ground, 60v goes to the backplate and variable voltage goes to the rear membrane.

 

[Matador]

I've run into a couple of issues with my build, one I've overcome, the 2nd I'm just digging into. 1st up was after completing my power supply I had no DC on the heater output, I had a full 9.5V of AC instead. After a lot of head scratching and a good nights sleep I determined that the heater section had no ground. Ground points were fine all over the board except the heater section so I ran a piece of wire on the backside of the board from the negative of C6 to a thru hole ground and  "Boom" I got a DC output at the heater terminal that adjusted to 6,3V like it was meant that way. Defective board? Not sure but it's working now.

This was covered a while ago:  look at post #1982.
https://groupdiy.com/index.php?topic=51377.msg760350#msg760350

 

[JCraft]

Thanks for the replies guys! I just took a piece of wire and jumped the pins on the power supply instead of installing the wiring block, it’s a permanent fix for me as I’ll never change it. I reversed the FC & RC as Tim stated and can tell the membranes changed with the front being the front now. One problem I didn’t mention before as I was thinking if I corrected any issues as I listed before it might work itself out, it did not. When I first fired the mic up I notice a fair amount of noise and the signal would periodically disappear, this is the same with either tube I have here, 12AY7 or 6072. The tone of the mic appears to  very good, brilliant top end and a decent low end. I thought maybe C10 or C11 might have been damaged because the drop out  in audio appeared to be slow, like a gate. So I replaced C10 & C11 with a couple of .0047uf/600V polypropylene orange drops of fairly recent vintage I had on hand, did not help. I’m slowly digging thru this thread from the front (page 20 now) as I thought I saw someone with a similar issue and a solution when looking for the info Matador so kindly provided provided above. I as stated  a few lines back it sounds like the mic is good tone wise with the exceptIon of the noise & drop outs.  Any help is greatly appreciated and thanks again!

 

[Tim Campbell]

make sure that the connections to the capsule are snug. They sometimes loosen when soldered

 

[JCraft]

make sure that the connections to the capsule are snug. They sometimes loosen when soldered

The only one I noticed was the rear backplate the lug was 0 ohms, but the screw was showing 100+ ohms. I didn't tighten it with a screwdriver I put a little pressure on the lug in the direction of tightening it and while it didn't move the resistance did drop to 0. Something odd I noticed is the resistance between ground in the power supply and the mic body when off is zero ohms, when on it goes to 154 ohms and the potential between the two goes to 0.03V when on. I'm sussing out my cable later, it may be suspect so I'll rule it out next. Thanks Tim.