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

[egroys]

Alright. What difference will the 1uf make? Can you possible link to a Mouser material number that could work?
I’ve read somewhere that I should go for Polystyrene & Tantalum capacitors.

You're going to have to source those on eBay, most likely. Search this thread about "coupling" caps and you'll see what folks say.

 

[magnusp71]

Both mics have Ami t14, 1uf 150v wet tantalum coupling cap, nos ge 6072. The differences are the type of 22uf cap ( I kept the value) and grid resistor value. Beesneez sounds better to me with an electrolytic 22uf and tim Campbell with a wet tantalum at that position.
As far as the grid resistor goes the beesneez is 250M and the ct12 30M.
I prefer the mic with stock/original values. It might not sound as impressive in the low end but I don’t need to touch the low end during mix. Plus the proximity effect is much more usable. The 250M to me sounds a little bloated and I always have to take some lows out during mix.

Hi there. Thank you for sharing this. Would really like to know which caps you ended up using (part number)?
I'm trying to find substitues for these to caps in the original BOM, but not really sure how to make sure that they fit the circuit and PCB

 

[Purplenoise]

Hi there. Thank you for sharing this. Would really like to know which caps you ended up using (part number)?
I'm trying to find substitues for these to caps in the original BOM, but not really sure how to make sure that they fit the circuit and PCB

Hey there. Since then I have changed a few things around after using this circuit in sessions. For the 22uf I use electrolytics…nichicon is pretty good. If you can’t find 6.3v you can use 10 to 50v since they are small enough to fit the circuit. I wasn’t very fond of elna silmic though that many people tend to use…or the much more expensive black gates.
As far as the output cap…I ended up with 1.7uf wet tantalum but surprisingly an electrolytic works there pretty good too. A more present upfront sound than the suggested film caps.

 

[magnusp71]

Hey there. Since then I have changed a few things around after using this circuit in sessions. For the 22uf I use electrolytics…nichicon is pretty good. If you can’t find 6.3v you can use 10 to 50v since they are small enough to fit the circuit. I wasn’t very fond of elna silmic though that many people tend to use…or the much more expensive black gates.
As far as the output cap…I ended up with 1.7uf wet tantalum but surprisingly an electrolytic works there pretty good too. A more present upfront sound than the suggested film caps.

Thank you so much.
I’ve ordered the 1.7uF wet tant for output and a 22uF wet tant for the C3 as well (will try with nichicon if it doesn’t sound as good as expected). These are the items:

Output:
https://www.mouser.dk/ProductDetail/74-109D175X9125C2

C3:
https://www.mouser.dk/ProductDetail/74-135D226X9075C6 or

https://www.mouser.dk/ProductDetail/647-UKW2A220MED

 

[Purplenoise]

Thank you so much.
I’ve ordered the 1.7uF wet tant for output and a 22uF wet tant for the C3 as well (will try with nichicon if it doesn’t sound as good as expected). These are the items:

Output:
https://www.mouser.dk/ProductDetail/74-109D175X9125C2

C3:
https://www.mouser.dk/ProductDetail/74-135D226X9075C6 or

https://www.mouser.dk/ProductDetail/647-UKW2A220MED

Oh wow…you got them from mouser. Those are way too expensive for any difference they might have on the circuit. I got them on eBay for..a fraction of new prices

 

[Potato Cakes]

Hello, Everyone,

I am trying to wrap up one of these builds but I cannot seem to get figure 8 to work. The relays are clicking and I get voltage to the the F8 solder point on the board when figure 8 is selected on the PSU. I get full signal from cardiod and omni. When I select figure 8 I get pretty much no signal. I thought the backplates were shorted together but they are not. I have confirmed with a multimeter that the relays are indeed working.

I have attached an image regarding two points that are unclear if they are to be soldered. Right now I do not have them connect as they were not in the instructions to do so but in several places in the build guide they look connected. Could someone verify one way or the other if the spots circled in red should be soldered together?

In omni and cardiod, I get about 30VDC on the respective capsule sides. In Figure 8, I get about 20V on the front and 3V on the back. Also in figure 8, I get about 1.1V on the FB but it is 0 on the other patterns. Could someone share what the proper voltages should be?

Thanks!

Paul

EDIT: It is not the one on the right. That kills omni as well

 

[Potato Cakes]

Also of note, when I inject signal to RC and FC in figure 8, I get much less signal at the output on FC than RC.

 

[Potato Cakes]

Found that C5 had been damaged and was shorting out the RC and FB. Changed it out, confirmed that it was now correct but still no figure 8. This is a good one.

 

[Potato Cakes]

Now with C5 being repaired, I have equal signal level when injecting tone into FC and RC. However the voltages are very different.

I also get signal levels on both cables when in cardiod, but only the front capsule has voltage which is expected. I am confused how audio is passing. From what I see on the schematic the signal is cut off from the rear capsule connection from the relays.

Thanks

Paul

 

[Potato Cakes]

So I found the problem but I do not understand why. C5, for whatever reason, keeps getting destroyed. After is in circuit and power is applied, they somehow short out or become very low impedance (4-100 ohms) This is killing the voltage on RC. When I remove C5, I get about 30V on FC sides and 20V on RC in figure 8 mode, which makes sense as there is a second resistor in series with RC in figure 8. I also now have signal through both capsules, with about half the signal on the rear. I take a new 1000pF cap (styrene, 630V) test it before soldering it in place, solder it in and retest, with both instances showing no shorts. As soon as I apply power, C5 fails and we're to the same problems as before. This is completely new one for me.

I'm going to call it a night. Try again tomorrow.

Thanks!

Paul

 

[rock soderstrom]

I can't tell you what exactly is wrong with your build, but I would like to remind you that voltage measurements in this area can be misleading due to the very high impedance.

Good luck.

 

[gyraf]

..and note that styrene caps are very sensitive and easily damaged by heat - impossible to solder with short leads. Try mounting with longer leads, possibly diverting the soldering heat with pliers at the lead

 

[Khron]

So I found the problem but I do not understand why. C5, for whatever reason, keeps getting destroyed.

I don't suppose you've considered trying out a different-film capacitor..? Even if just for a test...

 

[Potato Cakes]

That will be next. I have some PP's that I could use.

Thanks!

Paul

 

[Potato Cakes]

..and note that styrene caps are very sensitive and easily damaged by heat - impossible to solder with short leads. Try mounting with longer leads, possibly diverting the soldering heat with pliers at the lead

I am aware. I use them for lots of builds in the past but until recently, maybe only 2 or three were damaged in the build process. This one is strange because I test it in the circuit before powering on and everything is fine but the minute it is turned on that is when it fails. A bit of a head scratcher.

Thanks!

Paul