Mini u47 style mic

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Purplenoise

Well-known member
Joined
Sep 19, 2019
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531
Hey guys. Just wanted to share an interesting experiment with you.
Since I had a bunch of leftover parts I decided to make a mini u47 with a 13cw4 nuvistor in a microphone parts small body from a T12 kit.
The mic uses a small cinemag 8:1 transformer and 12ohm cathode resistor. I have a drop down resistor for heater but I am building a psu now to separate heater and B+. Used more or less modern components and the mic sounds fantastic. Not exactly a typical u47 sound but a more modern version of it. Very balanced and 3D sounding. Cheers.
 

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Same layout on phenolic board and closer to original components for a regular 47 body. Transformer is a custom Moby with extra windings but same ratio
 

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Cool :) So, it works?
No idea yet haha…waiting for the body still. The first one with the same layout ( first pics) works and sounds great. If I haven’t screwed something up it should work just fine..and sound even finer haha
 
No problems with that big resistor overheating on the first mic? Is it okay to mount to the rail like that?
 
So, if I remember correctly, this nuvistor arrangement is something you did in a previous U47, but something was different in regards to how Neumann did it right? The transformer ratio?
 
No problems with that big resistor overheating on the first mic? Is it okay to mount to the rail like that?
Yes it gets hot and maybe it won’t be good in the long run but I am planning on building a psu that separates H+ and B+.
 
So, if I remember correctly, this nuvistor arrangement is something you did in a previous U47, but something was different in regards to how Neumann did it right? The transformer ratio?
Yes. Either use a bv11 style/ratio transformer or keep the bv08 and change the cathode resistor to 12 ohms ( if you follow Neumann schematic just parallel a 27 ohm to the 68ohm resistor)
 
VF14 performance - I doubt it really

What "tube" is used in the circuit above? I think there's some real fakery going on: the 100K resistor dropping 39V indicates a "heater" current of 0.4mA (39v /100000 ohm) , i.e. a tube running off 0.0024 W heater power. I smell BS..

Could it be that the "Supertube" is no tube at all? :)

/Jakob E.
 
VF14 performance - I doubt it really

What "tube" is used in the circuit above? I think there's some real fakery going on: the 100K resistor dropping 39V indicates a "heater" current of 0.4mA (39v /100000 ohm) , i.e. a tube running off 0.0024 W heater power. I smell BS..

Could it be that the "Supertube" is no tube at all? :)

/Jakob E.
Hey Jacob, his posts are deleted I believe 😊
 
Hi Purplenoise. I'm curious what your aim is in separating H+ and B+. Are you aiming for something with the Nuvistor? I thought the beauty of the Nuvistor is it'll work with the existing U47 circuit deriving heater from B+. I really like this idea. For cheap or 'spensive.

Is the Moby transformer the 10:1 BV11?
 
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Hi Purplenoise. I'm curious what your aim is in separating H+ and B+. Are you aiming for something with the Nuvistor? I thought the beauty of the Nuvistor is it'll work with the existing U47 circuit deriving heater from B+. I really like this idea. For cheap or 'spensive.

Is the Moby transformer the 10:1 BV11?
No other reason than excessive heat in the mic…I don’t think there is an audible difference. I have two more 47 builds with the original scheme.
The transformer is a Moby bv08 with extra windings but same ratio as original
 
So the mic is finished and sounds fantastic.
Danys M7, Moby bv08, ge 13cw4, tubular ceramic for c1 and hydra mp 1uf for c2 and c3. The psu ( separate h+ and b+) is made by TLRT..
 

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