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

[poctop]

Finished a build with a Beesneez body and capsule. This thing sounds great. I fired it up with an EH 12AY7, replaced that with my 1953 five star from Bowie, then replaced the Polypropelene film cap with a wet tantalum. Not sure I could tell much difference between the two caps but I have a sinus cold and my ears are a little out of sorts.

The Beesneez body is beautiful and fits the board perfectly. I hope there's more projects in the future that the Sneesbys will customize a body for. It ended up being a steal of a deal with the package including the Beesneez CK12.

Thanks For taking the time to report you sucess 
Best,
Dan,

 

[Lordward]

Hi,

Can anyone point me to how I can calibrate this mic/psu?  I can't seem to find any info anywhere.

Cheers,
DW

 

[Lordward]

Hi,

Can anyone point me to how I can calibrate this mic/psu?  I can't seem to find any info anywhere.

Cheers,
DW

So, I'm slowly figuring this out.  I've been able to set B+ with the mic plugged at 110V,  the heater at 6.3V.
There is no voltage change when I switch patterns. 

The capsule voltage before the 8Mohms resistors reads about 54 V, is this ok?

Lastly, on the PSU board there is a variable resistor, R4 (250K), what does this adjust?

Thanks in advance!
DW

 

[Delta Sigma]

Since you sound new to this, remember that the PS will sting you. It may be fused but treat it like a live electrical panel. Same potential. Make sure you read the silkscreening on the circuit board. It indicates what each pot does. R3 is for adjusting the bias on the C12 (same power supply board). The jumper "CBON" shorts this pot out for an Elam 251. You can ignore it.

R12 adjust the heater voltage, though it sounds like you've got that one. R4 adjusts you B+ which should be 120V.

Getting your heater close is important and overheating is bad. Some people start with dummy loads on their B+ to check their PS. I just put in a 12AY7 from my guitar amp and plugged my mic in. Not a safe option especially if you're new to building. Best to start with a dummy load.

Here is how I calibrated mine:

I fired up my mic with the PS cover off and the mic body all together. I immediately checked the heater and B+ to make sure they were less than spec (B+ will rise as it warms). I checked the mic for audio through my DAW, switched patterns then adjusted B+ to roughly 115, expecting it to rise. I left it for an hour. I made up two mic cables for this guy (make sure you use the larger gauge wires for H+ and GND) and used the longer cable (more voltage drop) for calibration. I removed the mic housing (will be super noisy if you listen to it). I checked B+ at the PS and the B+ check pad on the mic. I also check the heater at the PS and the mic (be careful with leads around the lead termination of the board or the mic socket). Knowing the drops on the cable, I shut everything down, put in my NOS 6072a, put the mic housing back together, fired it up and checked voltage at the power supply. I let the tube burn in for quite a while and occasionally checked voltages at the PS. In the end I removed the mic housing and calibrated one last time using the B+ check pad.

Keep in mind the varying wall voltages in your area (will affect your B+, not your H+) and varying mic cable lengths if you have more than one. You want to keep B+ as close to 120VDC as possible and H+ keep from going over 6.3VDC.

My wall voltage is 121VAC and ranges from 120VAC- 123VAC in my city. Usually; commercial buildings will be different if 3 phase supply. The longer the mic cable the lower your voltage at the mic compared to the supply, especially with the heater.

You don't necessarily have to be that precise but I like to be. Hopefully more experienced builders will chime in if I mispoke.

 

[muffy1975]

Hi,

if this has been already covered can you point me to the post?

I'm using a Jan 12AT7 and was wondering what the cathode bias voltage should  be? What should it be for a 6072?

Are there any tweaks to be made for this valve to work?

I have removed the pattern switches so there is just the  cardiod pattern and hooked up one side of the capsule.

regards

Michael

 

[micaddict]

In the C12 thread, Matador offers some ideas for tweaking that circuit to the 12AT7.

The Ela M is not the same microphone, but it is based on the C12, of course.

 

[micaddict]

Here's the short version.

Microphone:  Change R17 from 100K down to 47K
PSU:  Drop R1 and R2 down to 33K.  Adjust R3 down to about 900ohms, then tweak with the actual tube.
Test load: decreases from 180K down to (120V/1.35mA) = 88K.  91K would work as a substitute for a real tube for PSU testing.

No doubt Dany can tell us how relevant this is for the Ela M and if he agrees with the tweaks in the first place.

 

[ding]

Hi,

if this has been already covered can you point me to the post?

I'm using a Jan 12AT7 and was wondering what the cathode bias voltage should  be? What should it be for a 6072?

Are there any tweaks to be made for this valve to work?

I have removed the pattern switches so there is just the  cardiod pattern and hooked up one side of the capsule.

regards

Michael

The 251 is self biased. No bias voltage from the PSU. Take a look at the schemo.

 

[micaddict]

Yup, that is a meaningful difference to begin with.

 

[muffy1975]

thanks Micaddict,

Ding, I know it's self biased  but changing the value of the cathode resistor will effect the bias. In this respect I wondered it it needed to be altered for an AT7. Should it be around 1V+????

Also on the topic of valves and the ELA M250/1 , with a 5840 valve/tube  is the wiring to the circuit ???

grid              pin 1
cathode      pin 2
Ground      pin 3 ( redundant heater )?

plate            pin 5+7 together

heater        pin 6                              =6.3V

Then cut pin 4+8 short. We don't need em.
And what  should the cathode voltage be here??

When i type 5840 into the search there is nothing on it with regards to hooking it up into the ela 251  circuit.

Thanks for any advice here.

 

[micaddict]

When i type 5480 into the search there is nothing on it with regards to hooking it up into the ela 251  circuit.

A 5480 tube does or did exist, but I guess you mean 5840?
That might be the culprit. 

Also, Dany's PCB kit is for the export version of the Ela M251, which has the 6072a tube. Officially, it would be Elam M251E.
The original, European version (non -E) had the subminiature AC701(k) tube.
I once asked Dany if he would make a kit for that one, too, but he hasn't sofar. And I know he's quite busy nowadays.
But perhaps a subminiature tube can be fitted without too many alterations to the existing kit. (?)

 

[poctop]

thanks Micaddict,

Ding, I know it's self biased  but changing the value of the cathode resistor will effect the bias. In this respect I wondered it it needed to be altered for an AT7. Should it be around 1V+????

Also on the topic of valves and the ELA M250/1 , with a 5840 valve/tube  is the wiring to the circuit ???

grid              pin 1
cathode      pin 2
Ground      pin 3 ( redundant heater )?

plate            pin 5+7 together

heater        pin 6                              =6.3V

Then cut pin 4+8 short. We don't need em.
And what  should the cathode voltage be here??

When i type 5840 into the search there is nothing on it with regards to hooking it up into the ela 251  circuit.

Thanks for any advice here.

better Check this out ,

http://groupdiy.com/index.php?topic=57902.0

 

[micaddict]

LOL

Man, I'm getting old!
And I was the first one there to reply, no less.

Thanks, Dany.

 

[Lordward]

Hi guys,

Well, after building one of these mics on the PCB kit I managed to get it working but after replacing the tube I broke the tube socket PCB off of the main PCB rendering it useless.  So, I took matters into my own hands and discovered this thread: http://groupdiy.com/index.php?topic=54078.0

Seeing this I decided to "copy" this and make a point-to-point version.  I found some pics online and saw that the relays were mounted on the back of the Plexiglass board so I did the same.  I used the D-251 schematic and managed to get this thing to work.  Yay! 

However, I seem to have the problem that when I have loud-isa vocals going through the mic it seems to have a bit of fuzzy distortion.  I've tried 3 different preamps with the same results.  I've also tried using a Electro Harmonix 6072, a NOS GE 5 Star 6072a and a cheap Chinese no name tube.  Always had the same results.  On quieter or mid loud vocals it sounds fantastic.  Really nice.  A bit bass shy but I haven't tried the tweaks yet.  Anyone have any idea what this could be?

Here's a pic of my build:

 

[Lordward]

Here's another pic (since I can only post 1):

 

[Lordward]

Responding to my own post:  I've realized that I've put in a wrong value resistor.  8M Carbon.  On the schematic I read 30M 1/2 W and I put in an 8. 

After putting in a 30M it sounded really odd.  Then I put in a 1M 3W.  Sounds a whole lot better now....but still distorts and louder levels.  Wish I understood why....

 

[ln76d]

Probably not without  a reason you used 8M. Schematic for AC701K version had this value instead 30M.
Where did you put 1M resistor? Instead 30M?
Did you used other values corresponding to the original schematic?
It's hard to see much here since you did wires spaghetti
What for is that 220(pF?) polystyrene capacitor?
Is it in parallel with another polystyrene?
What capsule did you used?
Did you measured any voltages inside microphone?
If not, i would start from plate voltage (before and after 100k), then cathode, heaters and finally polarisation voltage.

 

[Lordward]

Probably not without  a reason you used 8M. Schematic for AC701K version had this value instead 30M.
Where did you put 1M resistor? Instead 30M?

I'm using the - vintagemicrophonepcbkit.com d-251 "Walter White" - schematic.  Yes, I put it at R4

Did you used other values corresponding to the original schematic?

Very small:  I used 8.2M instead of 8 at R6 and R7.  At R3 and R5 I'm using 499K  instead of 500K.  At C3 I used 22uF instead of 20.  C2 I started with 100uF as suggested but ended up using 2x220.  On C1 I'm using a 1uF and also tried a 3.3uF.  I preferred the 1uF so far but the difference wasn't the world

What for is that 220(pF?) polystyrene capacitor?

C2, see above.

Is it in parallel with another polystyrene?

Yes, see above.

What capsule did you used?

I'm using this:  http://store.studio939.com/product/35mm-k67-style-capsule

Did you measured any voltages inside microphone?

Yes, I did and everything seemed to be within parameters.  I wrote it down somewhere....must look....

If not, i would start from plate voltage (before and after 100k), then cathode, heaters and finally polarisation voltage.

I'll find or re-measure tonight and post my readings.  I just wanted to point out that right now, even with a Generic cheap Chinese tube, the mic is sounding really good.  It's just when I push loud vocals into it that it starts to sound a bit broken up.  Maybe it just can't handle it by design? Thanks for your help!

 

[Lordward]

I just wanted to point out that right now, even with a Generic cheap Chinese tube, the mic is sounding really good.  It's just when I push loud vocals into it that it starts to sound a bit broken up. 

I just realized that I currently do not have the "no name" Chinese tube in it but rather the Electro Harmonix 6072.  In any case I have the same issue with both tubes.

 

[ln76d]

440pF is little bit too much for C2 or your capsule is overbrighted (yes these chinese "ck12" can sound different a little bit).
Desolder these caps, or at least both from one side, and make voice test.
R4 is another posibility and also can causing lack of low end.
1M is really too small, i would think about 100M or 1G but not 1M 
30M and 8M are also small values - but if you want to recreate something at least in 20% similar to the original then these are ok.
Rest differences of the parts are ok.
If this wouldn't help - try to change 22uF fine gold to something else (these caps sometimes can be tricky) if this not help, try different output cap, but JB usual works better than fine