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

[RuudNL]

¨All vacuum tubes and capacitors go through an extended burn-in period to ensure superior stability.¨

Then why did I receive some tubes that did not work at all, or had internal shorts!

I once ordered 60 pcs. JJ EF806S tubes straight from the factory. (As a company), to find later that my local distributor had them for a lower price. (Even including VAT and no shipping costs!)

 

[Evertide]

JJ "A rigorous final test for tubes and capacitors verifies every important parameter. In particular, the parameters for flawless tube functioning include insulation characteristics, vacuum level, cathode emission efficiency, filament voltage, plate currents, and microphonics. The quality control process includes several thousand hours of reliability testing on samples of tubes and capacitors. ¨
¨
Even I had GL34 shorting after a few hours , made a fine fuse tester..

 

[chrispbass]

Just helped a friend finish off a build that we’ve been working on when we’ve had time to get together.

Used Beesneez capsule, Moby transformer and GE6072A.

I’ve never built a mic before, and he’s certainly new to DIY electronics but is now hooked!

We finished it and tested it on the bench and all seemed well. He took it away to try in his studio and used it straight away on a session and is very happy. It’s currently in a ‘vanilla’ state, so there is a benchmark to refer to before spending some time tweaking component values.
.

A couple of things though…

1. The relays were just stopping the body from centralising to the top plate.
This was overcome by filing and elongating the top holes in the guide rails. This allows them (and the pcb to move over a few mm so the top plate centralises in the Aliexpress body.

2. He has mentioned that it does seem a little bit low on output and had to push his Avalon 737 s fair bit.

Is this typical with this circuit? Obviously I’m just relaying initial impressions at this point (and not in the room), or is there something else to look for?

3. H+ is dialled in at 6.3, B+ just shy of 120. Is there an optimum voltage for B+, or just open to experimentation along with swapping out some components to alter frequency response?

Anyway, thanks to Danny and everyone here for contributing to a great project and a really big shout out to @Jim50hertz who gave us lots of great advice outside of this thread.

Cheers
Chris

 

[rock soderstrom]

Yes, a couple of 701s would be really sexy. But I don't play the lottery, so I wouldn't try to buy from unknown sellers (not you....)

Personally, I think these "very rare" Siemens Halske triple Mica ECC801S with the brand/label sound pretty good (the ones with the two holes on the plate side and the round getter and the shield mica over the top/finger mica, I think it was the German Military Version). Most other Siemens ECC81s... are total junk, like the DDR models. In my opinion, these Siemens Halske ECCs sound a bit brighter and also have a bit more low end than the more roundly balanced GE6072s. I have 11 NOS GE6072s and 6 of them are unusable, both triodes of them. They crackle or have a higher noise floor. Of the 6 Siemens Halske ECC801S NOS tubes, 4 are excellent, two are also unusable for microphones, they also crackle. One thing is really great, the Siemens Halske clearly have a better background noise compared to the "good" GE6072. That's my opinion.

These are interesting statements, I have had similar experiences. Yesterday I randomly tested around 30 different ECC81/12AT7 type tubes for noise and in some cases also sound. These included Telefunken, Sylvania, Phillips, RFT, Valvo, Mullard etc. but also GE6072 5 star and Siemens ECC801.

The latter two types were clearly at the top, an astonishing difference. Some Mullard and Telefunken were also quite good, the rest were mostly pure "noise and crackle" horrorshow.

I have tested many used but also some NOS tubes, here is just a part of my ECC81 stock.



Testbed was "Goldie", a cardioid only M251 mod for SCT800.

 

[Luckyadnan]

guys what is the best capacitor for this project? i mean brand and uf? i need more dimension on the sound

 

[Delta Sigma]

guys what is the best capacitor for this project? i mean brand and uf? i need more dimension on the sound

AKG CK12. Maybe 70pF, variable with sound pressure

 

[Luckyadnan]

AKG CK12. Maybe 70pF, variable with sound pressure

for the diy 251 on the c1 by default 3.3uF CDET

 

[Luckyadnan]

for the diy 251 on the c1 by default 3.3uF CDET

im using solen 3,9Uf 400v and i feel the sound 3d is lacking and small (there is no chest sound)

 

[Luckyadnan]

i confusing to pick one of this, jantenz standar Z 3,3uf 400v, pio 1uf Russian green, SCR 3,3uF 400v, or this ERO W2 3,3 uF 250v

 

[Delta Sigma]

If you're trying to select a coupling cap, find the value that gives you the sound you want. Don't worry about the type or brand so much. I think I settled on a 1uF film cap in mine. 3.3uF is too big for most people. Schematic shows 1uF.

 

[Luckyadnan]

If you're trying to select a coupling cap, find the value that gives you the sound you want. Don't worry about the type or brand so much. I think I settled on a 1uF film cap in mine. 3.3uF is too big for most people. Schematic shows 1uF.

to be honest this is for the wa 251 mod project. the pcb look the same as this project. let me give a picture.

i plan for a mod of c3, c2 also.

and maybe the 30M on grid resistor

 

[Luckyadnan]

If you're trying to select a coupling cap, find the value that gives you the sound you want. Don't worry about the type or brand so much. I think I settled on a 1uF film cap in mine. 3.3uF is too big for most people. Schematic shows 1uF.

i hear on some audio hifi threads that the capacitor have a sound and sound different each other

 

[Delta Sigma]

i hear on some audio hifi threads that the capacitor have a sound and sound different each other

I’ve read a lot of things; here and elsewhere. Some were right, some were not. Try for yourself.

If you want my opinion, taking an existing mic and changing a cap dielectric type to improve the sound is like painting a car red and expecting it to go faster. If you expect the red car to be faster, you’ll feel like a NASCAR driver after it’s painted.

 

[Jim50hertz]

I’d like to try a 250m grid to ground. I only have 1/4watt. BOM specs 1/2watt. Can I get away with the 1/4 watt?

 

[rock soderstrom]

I’d like to try a 250m grid to ground. I only have 1/4watt. BOM specs 1/2watt. Can I get away with the 1/4 watt?

No problem AFAIK.

 

[Jim50hertz]

Thank you @rock soderstrom!

 

[egroys]

I've started my build and I am seeing that, from the BOM, R4 30M is 1/4watt instead of 1/2 like on the schemo. Is that ok?
I also see 392K ohm resistors that are on the PSU BOM...is this an error? PSU R9 is 392ohms and already included.

 

[rock soderstrom]

I've started my build and I am seeing that, from the BOM, R4 30M is 1/4watt instead of 1/2 like on the schemo. Is that ok?

Again, no problem. The grid to ground resistor sees almost no current.

I also see 392K ohm resistors that are on the PSU BOM...is this an error? PSU R9 is 392ohms and already included.

I couldn't find a 392K resistor in the PSU circuit at first glance...

 

[garp]

The 8x 392k resistors are for the pattern switch (replace stock resistors with 8 x 392k) .

 

[pasarski]

Never used a real one, but I know for sure that if you use good parts (the capsule is the most important one), it will be in the premium clone ballpark and will wipe the floor with the cheap ones.