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

[Greenie]

HI. I am having som issues with the 9v in the vintage mic pcb for the D 251. I get 9/4.5 allt he wat till r8, from one en to the other the voltage is 4.5 v and on the other side it is 2v'ish. So at the voltage regulator it is only 2 volt and at the other end it is mV's? R8 gets very hot. In the schematics included, the wattage is 1w on these 4.7Rs, but I have seen 5w indicated, (which is in my PSU), is 1w enough?

Also in the the includde schematics there is parts in blue print that is said to be omitted, is that so?

I

HI. I am having som issues with the 9v in the vintage mic pcb for the D 251. I get 9/4.5 allt he wat till r8, from one en to the other the voltage is 4.5 v and on the other side it is 2v'ish. So at the voltage regulator it is only 2 volt and at the other end it is mV's? R8 gets very hot. In the schematics included, the wattage is 1w on these 4.7Rs, but I have seen 5w indicated, (which is in my PSU), is 1w enough?

Also in the the includde schematics there is parts in blue print that is said to be omitted, is that so?

I am using an old Apex60 Psu as the base. The ground on the seven pin was for some reason connected to the ground and to pin 3. When i cut that, the voltage was suddenley 13,6v all the way after the regulator, turned it down to 6.3v. I don't know if it is the grounding thast did it, but it seem to work now.

 

[gearfreq]

Hello all! After no luck with getting any signal what so ever, I went ahead and bypassed the 2 relays (K1 and K3) needed to apply the Fig8 section via the D-250 Schematic posted in this forum (attached below). I hard wired to the corresponding pins on K2 relay and disabled the Fig8 wire from the PSU switch.

I am now getting output but my voltages to the FC and RC are around 33V and BP is around -130V (erratic) Should this be around 60V+ per capsule to be fully optimized with out 6dB of loss in gain? If so, what could be causing this to be cut in half? The 2 relays are still installed on the board but not activated. Any help would be great appreciated...almost there guys!!

B+ =120V
HEATER= 6.3V
PLATE =64V

 

[Delta Sigma]

You can't measure your capsule voltages correctly with a regular voltmeter;
https://groupdiy.com/threads/basic-microphone-troubleshooting-techniques.82241/post-1062213

 

[Delta Sigma]

@Greenie I'm responding here so we're not posting in the sticky thread. Measuring the 251 would be the same as the 49, measure your capsule voltage at the voltage divider where the impedance is lower. There is no current through R6 so no voltage drops across it. Measure at R3/R5. Do not measure at the capsule.

 

[johnsonic]

Hi All! Wondering if I'm missing something here. I was able to grab some panasonic DS2Y-S-DC6V relays and wasn't getting any switching at all. After looking into it some more and testing an extra relay I ordered, it looks as if the positive voltage is being applied to the negative side of the relay - so I don't get any pattern switching whatsoever. To confirm measurements - I'm getting +6.3V to the outside pin on K3 when in fig 8 (which is the negative pin).

Anyone see an easy way out or am I missing something?

Thank you!

 

[johnsonic]

It's weird - the datasheet shows the polarity as being reversed from what I see - when using the powersupply, as... well a power supply for my spare relay and applying the 6.3V to pin 1, pin 16 to ground - nothing.

Reverse that, and it works fine. Wonder if maybe I got a reject lot off ebay?

Here's a photo in case it helps.

 

[lightningbefore]

Hey @johnsonic! I had to buy a batch of these to try and just get one. I think I got mine from onlinecomponents.com or something. Haven't finished my Mata/Chung 251 yet even but I did start trying to get some of the out of stock components from Dany's list to eventually do that build too.

Yours looks very similar but Japan made rather than China made for mine and a few different #'s that I dunno what they mean. I have 10 so if you want to try one to compare PM me and I'll send it over

 

[gearfreq]

Thanks for all that helped me along the way with this build. Finally got it up and working. Being a newbie to this I have a few questions I am hoping someone help me with.

1. It seems I have to crank my preamp to around 60db + to get a decent signal. Almost the same as if it were a dynamic mic. Is this normal with this particular circuit?

2. I was able to purchase a 2uF 100V GE Wet Tant from ebay and was wondering what you guys thoughts on using it as the output cap? I know 100V is not that much considering the voltage jump during PSU power up, and could possibly damage the T14 and circuit. Are these caps able to handle this? I am only getting about 45V on the film cap (via Multimeter) but I do not have an ESR to measure capacitance during power up. Curious to hear the difference between a 3.3uF film cap vs 2uF wet tant.

Any info and help would be greatly appreciated. Thanks.

 

[johnsonic]

Hey @johnsonic! I had to buy a batch of these to try and just get one. I think I got mine from onlinecomponents.com or something. Haven't finished my Mata/Chung 251 yet even but I did start trying to get some of the out of stock components from Dany's list to eventually do that build too.

I don't think you need to send one over, but try putting pin 1 on the + side of a 9 volt (or to be safer, the heater feed from a power supply) and pin 16 to negative (or ground if using a PSU). You should hear a click. I don't unless it's reversed and therein lies my problem.

If you hear a click let me know and let me know where you found them! Desoldering everything to get to the relays and then desoldering them too sounds like a nightmare, so just have another board on the way. Currently rebuying parts.

Rök.

 

[gearfreq]

Anyone???

 

[wave]

Anyone???

There is a version of the 250/251 schematic from 01/1961 which has 1uF/160V as the stated output cap. I have used 1.7uF, 2uF and 3.3uF PP Films, PIO, and wet tants and didn't experience much difference in the values but the dielectric was more noticeable.
I wouldn't personally feel great about using a 100V rated cap in that position tho...

 

[gearfreq]

Hello all! I was finally able to get my mic up and running. I bypassed the 2 relays that correspond to the F8 pattern per the D-250 (no F8 option) schematic. My only issue now is that it appears that I am only getting OMNI on both Cardioid and Omni positions (both sides sound equally in gain without any proximity affect). I have a 4 wire isolated C-12 capsule (both backplates are bridged) I am getting 6+V to the relay (at the R test point) when switched via PSU. The mic sounds great but I am not getting Cardioid nor the desired low end because of OMNI config. What could be causing this? I traced everything from the 250 (Card/Omni) schematic.

 

[Delta Sigma]

Hello all! I was finally able to get my mic up and running. I bypassed the 2 relays that correspond to the F8 pattern per the D-250 (no F8 option) schematic. My only issue now is that it appears that I am only getting OMNI on both Cardioid and Omni positions (both sides sound equally in gain without any proximity affect). I have a 4 wire isolated C-12 capsule (both backplates are bridged) I am getting 6+V to the relay (at the R test point) when switched via PSU. The mic sounds great but I am not getting Cardioid nor the desired low end because of OMNI config. What could be causing this? I traced everything from the 250 (Card/Omni) schematic.

Backplate not connected or backplate screw not tightened? Be very careful checking this, it takes very little torque to shear these tiny screws.

 

[gearfreq]

Backplate not connected or backplate screw not tightened? Be very careful checking this, it takes very little torque to shear these tiny screws.

Delta! You are the man! I just need to tighten it one whole turn and viola! I was worried I'd strip out or shear off that screw when I started to feel abit of resistance. Btw I came across an old tread where you had mentioned of putting two 4uf+ 75 Volt wet Tants caps in series for the output cap to make 2uf+ 150V. Will this work without blowing the transformer open? I do know that I have a slight spike when powering up the psu but nothing near 150V. Anyways I appreciate you for all your help. I am learning quite a bit. Thanks

 

[Delta Sigma]

Buy film caps of different values to find what you like. That will make a bigger difference than dielectric types. Find a value you like, then try different dielectrics.

If you are using a true T14/1, like Moby's, don't bother with NOS caps. Find something that you are sure won't leak DC. The windings are extremely fine on Moby's T14/1 and can be damaged by a leaky cap.

 

[neowalla]

I

I am using an old Apex60 Psu as the base. The ground on the seven pin was for some reason connected to the ground and to pin 3. When i cut that, the voltage was suddenley 13,6v all the way after the regulator, turned it down to 6.3v. I don't know if it is the grounding thast did it, but it seem to work now.

I noticed that pin 3 and 7 are tied together in all my Apex 460 cables as well. from what the search engines are telling me, this is the Neumann standard cable pinout for tube mics.
1. white audio +
2. black audio -
3 and 7 thick blue and shield.(ground)
4. thick red heater.
5. yellow 120volts
6. green 0-120volts
and the 7th grey conductor is cut short and isolated.

However on this circuit pin 3 is "omni".

 

[neowalla]

I noticed that pin 3 and 7 are tied together in all my Apex 460 cables as well. from what the search engines are telling me, this is the Neumann standard cable pinout for tube mics.
1. white audio +
2. black audio -
3 and 7 thick blue and shield.(ground)
4. thick red heater.
5. yellow 120volts
6. green 0-120volts
and the 7th grey conductor is cut short and isolated.

However on this circuit pin 3 is "omni".

In searching through this thread to find the answer to this, I found this discussion came up a few years back. Look for response numbers 266-267 (look in the upper right of the blue border that gives the date and time of the response and you will see they are all numbered)
The "Neumann standard" for 7-pin cabling has pin 3 and 7 joined together with the shield, but on the schematic for this build pin 3 is one of two connections to the relays for pattern switching and the shield terminates to the ground lug on the XLR connector itself rather than that and one of the pins.
I'm going to build a cable for this microphone just to avoid any crossed wires, and label it accordingly so I don't use another 7 pin cable with pin 3 going to ground by mistake.

 

[Afzelius]

Hey! I just finished my second ELA M. The first one is working perfectly but I'm having a problem with the second one. The cardioid pattern is working well but when I switch to the figure 8 and omni polar patterns the mic fades out and goes silent after a short while. And the rear backplate never responds on those patterns either. I have been doing some tests and the only possible reason I can think of is that the K1 and K3 relays are dead. I had to file just a tiny bit of the sides of them so that they would fit in the mic since the yellow ones weren't in stock. Could this have destroyed them? Does anyone see another possible reason for this problem?

 

[egroys]

Just getting prepped to purchase components and I wanted to verify if I can use the resistors from my U67 dummy load
(210k ohms for B+, 33 ohms 2W for H+)?

Thank you in advance!

 

[egroys]

Can anyone tell me if either these TE connectivity or these TXD2 are a viable alternative for the relays on the BOM?