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

[axlreddy]

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.

 

[Tim Campbell]

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.

 

[axlreddy]

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?

 

[Tim Campbell]

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?

 

[axlreddy]

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.

 

[Tim Campbell]

check from the backplate all the way to the power supply. The fault is on that connection. A reversed component or a bad connection.

 

[tommymariot]

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?

 

[tommymariot]

other photo

 

[duantro]

Might need to file edge of relay slightly, if it is soldered and flush to pcb.

 

[tommymariot]

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?

 

[tommymariot]

Are these values correct for this mic?

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


H+ 6V/0.175A=33R 2W

 

[Banzai]

Heater current of 6072 is 350mA

 

[buckethead]

Heater current of 6072 is 350mA

There's only one system in use -> only one to heat -> 175mA

 

[Banzai]

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.

 

[buckethead]

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

 

[Banzai]

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.

 

[JessJackson]

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]

Hi guys,

Out of interest what have people using as bridging wire?

 

[Delta Sigma]

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).

 

[Delta Sigma]

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.