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

[Melodeath00]

^

doing a wet tantalum search on the Vishay website yields some series of caps at higher voltages (180-200+) and appropriate capacitance. Don't know if any are OK for this application.

They may sell them to you although I wonder what the MQ would be

I just tried this. I'm not finding anything over 125V for 3.3uF. Got a link? MQ on mouser is like 25 pieces at $60 each

 

[bockaudio]

Good point, David Bock. I have been unable to find any wet tantalums over 125V in the 3.3uF range, and they are very expensive. Do you think it's really worth it sound-wise, and is it dangerous to use a cap of 125V? And wouldn't it be dangerous for the transformer if the wet tantalum goes caput? I read that they short when they fail.

I've never seen the wet tant in a 251 short out (I have seen loss of capacitance), though I've seen plenty of tants short out in ATR124 decks taking down the whole machine (smoke optional).
I have also seen original T14/1 xfmrs go open. That wire is mighty fine.
IF your new build mic does not copy the exact footprint of the 251, you should have more room for other cap options. Then you can listen and decide for yourself. But in a vintage 251, space is at a premium so the original cap is a must, unless you are willing to crack the plexiglass body, as some repairs guys are willing to do. FYI there is no electrolytic that will fit in that space that sounds good so don't bother.
Yes you can use a 125v cap, though it's safer with higher tolerances. The occasion of reaching 125v across the cap occurs at power up, when the B+ is there but the tube hasn't fully heated. Reaching full B+ once the tube is heated will likely not happen during normal use, unless you stick it in a kick drum.
I have found NOS went tants (of the value you need for this mic), even recently, so I know they are out there 

 

[poctop]

Good point, David Bock. I have been unable to find any wet tantalums over 125V in the 3.3uF range, and they are very expensive. Do you think it's really worth it sound-wise, and is it dangerous to use a cap of 125V? And wouldn't it be dangerous for the transformer if the wet tantalum goes caput? I read that they short when they fail.

I've never seen the wet tant in a 251 short out (I have seen loss of capacitance), though I've seen plenty of tants short out in ATR124 decks taking down the whole machine (smoke optional).
I have also seen original T14/1 xfmrs go open. That wire is mighty fine.
IF your new build mic does not copy the exact footprint of the 251, you should have more room for other cap options. Then you can listen and decide for yourself. But in a vintage 251, space is at a premium so the original cap is a must, unless you are willing to crack the plexiglass body, as some repairs guys are willing to do. FYI there is no electrolytic that will fit in that space that sounds good so don't bother.
Yes you can use a 125v cap, though it's safer with higher tolerances. The occasion of reaching 125v across the cap occurs at power up, when the B+ is there but the tube hasn't fully heated. Reaching full B+ once the tube is heated will likely not happen during normal use, unless you stick it in a kick drum.
I have found NOS went tants (of the value you need for this mic), even recently, so I know they are out there

Dear Bockaudio, thanks For your Valuable input in this thread,
Best,
Dany,
dD

 

[micaddict]

David rocks.

 

[granger.frederic]

Great work guys
is there any issue with the relays in the high impedance section ?
what's the inter-electrode insulation/capacitance of the relays ?

 

[poctop]

Great work guys
is there any issue with the relays in the high impedance section ?
what's the inter-electrode insulation/capacitance of the relays ?

Thanks, Works Fantastic , All critical connection to the relay are floating off  board.

see here:
http://dk.mouser.com/Search/ProductDetail.aspx?R=DS2Y-S-DC6Vvirtualkey66710000virtualkey769-DS2Y-S-DC6V

Best, 
Dan,
dD

 

[JessJackson]

Well done Dan in taking over the project... It was too much for me to get done with everything else going on at the moment.

I do think maybe take a look at our last design (version 6.5) as this was the closest i feel to perfection in utilizing the relays.


The cathode bypass components would be floating on back of tube base hence displayed off of the board.

As per the coupling cap being wet tant, i have a few here, they are pretty much the 1501 if i remember correctly and I feel they don't sound bad they just over compress. I didn't like them in my elam builds but thats me.

Cheers

J

 

[JessJackson]

i also feel there should be more space on your build to accommodate longer resistors such as vintage wire wound types which can be sourced.

 

[Woot]

^

doing a wet tantalum search on the Vishay website yields some series of caps at higher voltages (180-200+) and appropriate capacitance. Don't know if any are OK for this application.

They may sell them to you although I wonder what the MQ would be

I just tried this. I'm not finding anything over 125V for 3.3uF. Got a link? MQ on mouser is like 25 pieces at $60 each

http://www.vishay.com/capacitors/tantalum/tantalum-wet/

They look like the XTK model. Datasheet is there too...

 

[Melodeath00]

Good point, David Bock. I have been unable to find any wet tantalums over 125V in the 3.3uF range, and they are very expensive. Do you think it's really worth it sound-wise, and is it dangerous to use a cap of 125V? And wouldn't it be dangerous for the transformer if the wet tantalum goes caput? I read that they short when they fail.

I've never seen the wet tant in a 251 short out (I have seen loss of capacitance), though I've seen plenty of tants short out in ATR124 decks taking down the whole machine (smoke optional).
I have also seen original T14/1 xfmrs go open. That wire is mighty fine.
IF your new build mic does not copy the exact footprint of the 251, you should have more room for other cap options. Then you can listen and decide for yourself. But in a vintage 251, space is at a premium so the original cap is a must, unless you are willing to crack the plexiglass body, as some repairs guys are willing to do. FYI there is no electrolytic that will fit in that space that sounds good so don't bother.
Yes you can use a 125v cap, though it's safer with higher tolerances. The occasion of reaching 125v across the cap occurs at power up, when the B+ is there but the tube hasn't fully heated. Reaching full B+ once the tube is heated will likely not happen during normal use, unless you stick it in a kick drum.
I have found NOS went tants (of the value you need for this mic), even recently, so I know they are out there

Thanks for that info! May I ask where you found those NOS wet tants, or am I off on a treasure hunt? I didn't see the right ones at Surplus Sales.

^

doing a wet tantalum search on the Vishay website yields some series of caps at higher voltages (180-200+) and appropriate capacitance. Don't know if any are OK for this application.

They may sell them to you although I wonder what the MQ would be

I just tried this. I'm not finding anything over 125V for 3.3uF. Got a link? MQ on mouser is like 25 pieces at $60 each

http://www.vishay.com/capacitors/tantalum/tantalum-wet/

They look like the XTK model. Datasheet is there too...

Thanks! Strange they did not show up when I used the Search Filters, but I see them now. This could be a good option if Vishay will sell them in low minimum quantities.

 

[JessJackson]

I think they are actually 1501's

TE-1501 capacitor

http://www.ebay.com/itm/SPRAGUE-30D-TE-1501-CAPACITOR-2-150-DC-NNB-/360167699030

the 1501 is what telefunken usa use in their reissues, although thats not really saying much. sorry

 

[poctop]

I think they are actually 1501's

TE-1501 capacitor

http://www.ebay.com/itm/SPRAGUE-30D-TE-1501-CAPACITOR-2-150-DC-NNB-/360167699030

the 1501 is what telefunken usa use in their reissues, although thats not really saying much. sorry

thanks Jess for the pointer,
Best,
DAN,

 

[Winetree]

Stuffing the board now. Maybe I missed something.
What's all this about a WET Tant? Should I get the part in the above E-bay Link?
Where does it go?

 

[Melodeath00]

The TE-1501 appears to be aluminum cap, not wet tant. It's for the coupling cap. It does indeed look like the caps Telefunken USA uses quite a bit in their reissues.

 

[trans4funks1]

I'm not sure how it applies but here is info on the Sprague:


http://www.vishay.com/docs/42042/te.pdf

http://www.mouser.com/ProductDetail/Vishay-Sprague/TE1501-E3/?qs=sGAEpiMZZMtZ1n0r9vR22beeiJoI0EpCZ9lzI8RKauE%3d

 

[poctop]

Here is a drawing of the factory two five one with the figure 8 routing through the the switch. It helped me to look at this to confirm that I had drawn the relays correctly.

I will appreciate it if any or every one can check my work in progress and offer correction(s) if they spot any mistakes.

For Reference.

I Posted the Schematics for you to compare see page 1,
Best,
DAn,

 

[trans4funks1]

Thanks very much Dany!

I look forward to going through step by step. 

 

[trans4funks1]

Hi Dany,
I was looking at your D-E251E schematic and comparing it too the AKG ELA M251E schematic, both of which are linked to in the first post of this thread.

I am curious about the polarity shown in the D-E251E schematic for the Cathode Capacitor that you have labeled C3, 22uf 6V. The traditional AKG schematic has the polarity shown the other way so I am bit confused and thought I should ask about it.

?

Thank You.

 

[poctop]

Hi Dany,
I was looking at your D-E251E schematic and comparing it too the AKG ELA M251E schematic, both of which are linked to in the first post of this thread.

I am curious about the polarity shown in the D-E251E schematic for the Cathode Capacitor that you have labeled C3, 22uf 6V. The traditional AKG schematic has the polarity shown the other way so I am bit confused and thought I should ask about it.

?

Thank You.

ErraTum

Many Thanks For Catching This , it is indeed inverted , this will be corected in the production batch as this are prototype pcb  , the silkscreen for C3 on the tube socket board should be inverted
so the (+) on the pcb should be the negative (-) side , for those who have got the proto pcb form the intial run , i sent an email to all of you to warn about this erratum , To fix this orient the capacitor C3 + lead on the negative on the pcb

Best,
Dan,

 

[Winetree]

Got it. C3 inverted.