Telefunken ELA M 251 Clone Tube Microphone Build Thread (D-Ela M 251E)

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Delta Sigma

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Purplenoise said:
Measured it, it is 3.4 actually. If I am not mistaken I read in one of your posts that you used two 6.8uf 75v in series ( 3.4uf 150v sum). I found two Siemens on eBay with those values so I am gonna give it a try since it looks like a very simple and effective solution. How did that work out for you? Thanks.

Sorry, I didn't do that but I don't see why it wouldn't work. I believe Fender used to do this to get higher voltage filter caps in some amps (CBS era?).

Remember, as long as you're being safe and not exceeding the ratings of components,  do what you can to set up a good comparison. The only thing that I'll add is that you should record before and after each change, listen back, wait a day, then give it another listen. I've made a decision on a component swap, then listened back to the recordings later only to find that I'd changed my mind.

Some people prefer to test component changes with instruments that have a wide frequency content and some prefer to use their voice because you know you're own voice well. I do the latter.
 

Purplenoise

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Sep 18, 2019
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Delta Sigma said:
Sorry, I didn't do that but I don't see why it wouldn't work. I believe Fender used to do this to get higher voltage filter caps in some amps (CBS era?).

Remember, as long as you're being safe and not exceeding the ratings of components,  do what you can to set up a good comparison. The only thing that I'll add is that you should record before and after each change, listen back, wait a day, then give it another listen. I've made a decision on a component swap, then listened back to the recordings later only to find that I'd changed my mind.

Some people prefer to test component changes with instruments that have a wide frequency content and some prefer to use their voice because you know you're own voice well. I do the latter.
Thanks, yes I try to keep track haha...I have a bunch of messy test sessions. Voice and acoustic guitar usually tell me a lot about a mic.
 

Purplenoise

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Hello electron wizards. I started my d251 build and I am a little stuck. I finished the psu but I don’t get any reading on the B+ ( on the screw green pad). I am including some pics of the wiring in case I did something stupid. Thanks guys.
 

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Purplenoise

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Delta Sigma said:
Check voltages on both sides of R1 & R2 and the B+ side of R4.
Thanks. I get proper voltages on both sides of R1 and R2.  R4 is the variable resistor, how do I properly check voltage to R4 without lifting pcb ? Where should I measure with multimeter?
 

Wilks978

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OK so I built a 251 inspired mic from Matador and chunger I been seeking help and support but to little success, I even replied to the forum I know this isn't the correct forum but I'm hoping someone could help me out I had multiple issues bad styroflex caps but replaced those styroflex caps with silver mica and still no audio I rewired the t14 transformer and either way no audio I checked the ohms and they are correct I even wired them to direct output cap and ground points capsule is working fine I'm really not sure what the issue is could anyone help please? I'm getting 61v to the capsule c1 r17 r13 r12 polarity is good I'm also getting 124v and 6. 3v directly to the tube pin 5  someone please

Some pics here
https://ibb.co/9Yzkh2J
https://ibb.co/wg7N1YN
https://ibb.co/GVTY5GW
https://ibb.co/f8wdYKJ
https://ibb.co/JKJwwcj
https://ibb.co/cXt5J1T
 

Delta Sigma

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Winnipeg
Purplenoise said:
Thanks. I get proper voltages on both sides of R1 and R2.  R4 is the variable resistor, how do I properly check voltage to R4 without lifting pcb ? Where should I measure with multimeter?

Too many social distancing beers last night... I meant R6. If you have voltage at R2 but not the B+ side of R6 it could mean a bad R4 pot or a missed solder point on the R4 pot.
 

Purplenoise

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Delta Sigma said:
Too many social distancing beers last night... I meant R6. If you have voltage at R2 but not the B+ side of R6 it could mean a bad R4 pot or a missed solder point on the R4 pot.
Hahaha...ohhh the good life lol. I’ll check tonight when I get home. I had a feeling as I was measuring voltages last week that R4 could have been the issue so I ordered a couple of more and I already replaced it but the issue remains. I’ll check again and let you know. Thank you so much.
 

Purplenoise

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Delta Sigma said:
Too many social distancing beers last night... I meant R6. If you have voltage at R2 but not the B+ side of R6 it could mean a bad R4 pot or a missed solder point on the R4 pot.
Ok just checked and you are right. No voltage on either side of R6. Is it possible the second R4 trim pot to be faulty as well? That’s so strange. I have one more but since I have two failed in the same spot maybe I am missing something?
 

Purplenoise

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Delta Sigma said:
Too many social distancing beers last night... I meant R6. If you have voltage at R2 but not the B+ side of R6 it could mean a bad R4 pot or a missed solder point on the R4 pot.
Ok swapped yet another trim pot for R4 and still no B+...any ideas why I am not getting any voltage beyond R4, at R6? Thanks.
 

TillM

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Wilks978 said:
OK so I built a 251 inspired mic from Matador and chunger I been seeking help and support but to little success, I even replied to the forum I know this isn't the correct forum but I'm hoping someone could help me out I had multiple issues bad styroflex caps but replaced those styroflex caps with silver mica and still no audio I rewired the t14 transformer and either way no audio I checked the ohms and they are correct I even wired them to direct output cap and ground points capsule is working fine I'm really not sure what the issue is could anyone help please? I'm getting 61v to the capsule c1 r17 r13 r12 polarity is good I'm also getting 124v and 6. 3v directly to the tube pin 5  someone please

Some pics here
https://ibb.co/9Yzkh2J
https://ibb.co/wg7N1YN
https://ibb.co/GVTY5GW
https://ibb.co/f8wdYKJ
https://ibb.co/JKJwwcj
https://ibb.co/cXt5J1T

Do you try another tube ?
Do you see your tube burn or not ?
The voltages look good.
Check continuety between your audio pins for xlr.
We need some infos ?
Where do you live, which capsule do you use and which tube (seams like GE 6072).
 

Wilks978

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TillM said:
Do you try another tube ?
Do you see your tube burn or not ?
The voltages look good.
Check continuety between your audio pins for xlr.
We need some infos ?
Where do you live, which capsule do you use and which tube (seams like GE 6072).

The capsule works fine I switched it to another mic it's a k67 from advanced audio, I have checked the XLR pins and everything seems to read correctly for pin 6 and 5 on audio this doesn't make sense, I have swapped 2 different tubes and they light up I only get some low audio after I crank my preamp to max 75db
 

TillM

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that's what i mean, if the voltage are right, check the continuity from the audio pins from the microphone to the xlr out.
You have to check step  by step to prove which not work right.
You know, that your capsules is good, your tube burn, your voltage looks good.
So now we have to check other parts.
You said in another thread that zu had to repair your mic body.
Please check also the grounding continuity from every single part who must have grounding (look at the schematic).
Please clean your pcb ! (especially the area where your cables goes to the mic).
C3 need polarity, as far as I see you use a normal film capacitor (which is okay), but i would also check it out.
When you get low audio, when you crank up the pre, most of the time when I had this, it was a grounding issue.
So I would proper check the grounding again.
Check if your transformer primary has the right direction.
I don't know exactly how the cinemags are wired, but check if you don't reverse ground on the transformer.
 

Purplenoise

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As I am still waiting for the ck12 capsule and a nos he tube I installed a Chinese k67 style and a Jan 6072 just to test voltages and noise. Voltages look good and calibration was a breeze. Quiet as a mouse too. Even with the k67 it sounds pretty good...a little 10k heavy of course but really smooth. Can’t wait for the proper capsule and tube.
 

Purplenoise

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So the mic is finally finished. BeesNeez ck12, cinemag transformer and wet tantalum caps. It’s quiet and it sounds...like a cross between a c12 and a u47 haha. I am thinking of ordering a Tim Campbell ct12 to try out. It sounds “related” but more mid forward than our Tele c12 with a little less high end. Is it supposed to sound like this? Is there anybody here that compared a c12 to a 251? Thanks.
      ————UPDATE————

Changed the cable to a good quality Gotham and recalibrated WOWWW...what a difference. Much more open, dynamic and unconstricted. Now the difference is what I would expect between a 251 and a c12.
 

Celinara

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Oct 7, 2015
Messages
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So i got the build a long time ago, built it, has some issues but due to life, im only finally getting around to getting it fixed and working. I've built the mic and psu, have a b+ at 117V and a heater at 6.29V. I'm having an issue that I can hear any tapping on the frame that its mounted in, but the level of it if you try to speak/get audio from the capsule, its almost 0 output. (maxed out preamp and only get a low signal). I'm testing it with the chinese tube the Apex 460 came with, but i have a NOS 6072 for it once everything works. Its a TC CT12 capsule and AMI T14. Any assistance would be fantastic!

edit: I noticed that my heater voltage drops to 0.03 when its set to omni, but on card and f8 its 6.29V.
 

Purplenoise

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Sep 18, 2019
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Ok a little experimentation. I installed sockets for C3 so I can easily swap different values/types. Apparently this cap plays a big role on the sound of the mic. I had a 100uf wet tantalum there and although the sound was really smooth it lacked a little mid information and it was a little bloated in the lower mids...it sounded great by itself but in the mix it was a little...too smooth. Switched to the 22uf from the bom and the sound is more balanced...not as smooth but much better timbral balance and even closer to our tele c12. The low end is perfect now and there is a forwardness that cuts through the mix in a very pleasing way. Here are the details for the components used:
-Grid resistor 250M
-coupling cap 3uf 150v wet tantalum
-BeesNeez ck12
-cinemag 13114
-jan ge 6072a from the 80’s

I’ll swap soon for a wet tantalum 22uf to see if the type plays a role there.
I am building now my second one with Ami trafo and tim Campbell capsule.
 

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