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

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Hi,
I just finished my D251E, but all patterns sounded like cardioid.
I follow the schematic which made by Trans4funks1 on page1.
Here's my connection:
--------------------------------
7-XLR to Mic PCB
1- audio +
2- audio -
3- omni
4- heater
5- B+
6-  F8
7- GND
---------------------------------
AMI T14 to Mic PCB
1st pair
red - S+
Blue - P+
2nd pair
red - S-
blue - P-
----------------------------------
PSU 7pin-XLR connection
1 - pin2 on XLR3
2 - pin3 on XLR3
3 - pin1 on pattern switch
4 - heater on PCB
5 - B+ on PCB
6 - pin3 on pattern switch
7- GND to XLR3

The capsule is Tim's CT12.

I really need recommend.

Thanks.
 
axlreddy check that you have a good connection to the rear membrane and backplate. Sometimes soldering can loosen the connection. Your capsule has 2 sets of connections to the backplates.  Perhaps try changing the connection to the rear backplate to the other side.

 

Attachments

  • dual connections.jpg
    dual connections.jpg
    48.1 KB · Views: 42
Tim Campbell said:
axlreddy check that you have a good connection to the rear membrane and backplate. Sometimes soldering can loosen the connection. Your capsule has 2 sets of connections to the backplates.  Perhaps try changing the connection to the rear backplate to the other side.
Thanks for reply, I've checked the connection and changed the rear backplate to the other side, but the problem still there.

BTW, I got the sound on rear membrane only on omni after changing the backplate.(FB to RB, RB to FB)
Did it mean something?
 
That just means that the capsule is working and the problem is with your connection to the rear backplate. Trace that cable back to the power supply.  Perhaps the relays?
 
Tim Campbell said:
That just means that the capsule is working and the problem is somewhere else. Perhaps the relays?
Hi, Tim

Which one did you mean?
Relay on mic or relay on PSU?

I've some scratch on relay on mic.
(K1&K3, see the pic below with red circle)
Did it matter?
Sorry about that sounds a stupid question.
I'm new here.

Best
Axlreddy.
 

Attachments

  • 20180705_210538~1.jpg
    20180705_210538~1.jpg
    67.7 KB · Views: 60
check from the backplate all the way to the power supply. The fault is on that connection. A reversed component or a bad connection.
 
Hi Guys, I'm building a D-ela M 251E. I'm using poctop's pcb and chunger HT-11A body but I found my mic doesn't close.
Photos in attachments.
Can you help me to solve the problem?
 

Attachments

  • IMG_1911.JPG
    IMG_1911.JPG
    1.9 MB · Views: 57
I just finished the mic and now I'd like to test the PSU with a dummy load. Can you suggest me some good values for a dummy load for this mic?
 
Are these values correct for this mic?

B+ 120V/0.5A=240K 1/4W


H+ 6V/0.175A=33R 2W
 

Attachments

  • Schermata 2018-11-25 alle 23.40.51.png
    Schermata 2018-11-25 alle 23.40.51.png
    155.3 KB · Views: 29
buckethead said:
There's only one system in use -> only one to heat -> 175mA

Fair enough. I always wire voltage to 9, and both 4+5 grounded.
 

Attachments

  • 6072.png
    6072.png
    10.1 KB · Views: 20
Is there any reason why you're doing that? Sorry for the off topic talk - but would be interesting to know

As far as I remember, C12s only heat one half too. And some DIY clones use different systems each for stereo pairs, so you can swap tubes between mics, get more life out of those things...not a good idea to poison cathodes there
 
Just a habit of always tying off everything unused and open to ground – everywhere, not only the tube. Gives me quiet builds, so guess I just stuck with it.

I'll give it a try on the next one, and leave one heater open.
 
wasup guys I've been using my 251 more and realized that the waveform it creates is lop sided, asymmetrical (heavier towards the bottom)

what do you think could be causing this? the tx?
 
PG_Sax: by bridging wire, are you referring to the hi-z wiring? Chunger sells a nice little package of small gauge Teflon (PTFE) coated stranded wire. I've also purchased some from Apex Jr but if you're not building a lot of gear, buying rolls of of different colours is way too expensive making Chunger's store your best bet.

Wherever you get it, get something small (26AWG or so), Teflon coated (not only heat resistant for soldering but also very hi-z) and stranded (less microphonic).
 
JessJackson said:
wasup guys I've been using my 251 more and realized that the waveform it creates is lop sided, asymmetrical (heavier towards the bottom)

what do you think could be causing this? the tx?

Jess, any progress on this? Does the mic sound OK? Did you view a waveform with a scope? Is your DC on (is the waveform asymmetrical or is it riding DC)? What is your quiescent current (measure VDC across R2 at idle)? Do you have another tube to try? Any hum?

I'm not the best around here for support like this but I noticed no one else replied.
 
Back
Top