D-47 or D-EF47?

[neowalla]

Hello everyone,
I just got an Art T4, a U47-looking mic. Well built, nice thing. It sounds pretty good as is, albeit a little noisy. From what the interwebs tell me, they are rebranded Alctron MK-47's. I want to rebuild it with one of the circuits from vintagemicrophonepcb.com, but I'm not sure which to choose. The D-47 with the twin 6028 pentodes, or the D-EF47 with one of the "EF" tubes? I've been trying to find some information on the merits of each design, but no joy. Can anyone point me to a discussion or some reference material describing the differences between these two circuits? Thanks in advance.

 

[RuudNL]

Build the one with the twin 6028 'if you like it hot'.
This microphone gets very hot, you can almost heat a room with it...
(A couple of years ago I have built this microphone for a friend.)

 

[Purplenoise]

Hello everyone,
I just got an Art T4, a U47-looking mic. Well built, nice thing. It sounds pretty good as is, albeit a little noisy. From what the interwebs tell me, they are rebranded Alctron MK-47's. I want to rebuild it with one of the circuits from vintagemicrophonepcb.com, but I'm not sure which to choose. The D-47 with the twin 6028 pentodes, or the D-EF47 with one of the "EF" tubes? I've been trying to find some information on the merits of each design, but no joy. Can anyone point me to a discussion or some reference material describing the differences between these two circuits? Thanks in advance.

They are both very nice. The d-47 might be closer to the “47” sound since this tube configuration matches the bv08 better ( no first hand experience but after a lot of reading here that’s what it seems to be). Also a little harder to find good quiet tubes than the d-ef47.
The d-ef47 sounds great, especially with m7 style capsules, and might be more versatile than d-47…and still a 47 family sound. In mine I used a terrapin toroidal transformer with 7.5:1 ratio to match it better with the ef800. With the bv08 it was lacking a little at the ends of the frequency spectrum

 

[neowalla]

In mine I used a terrapin toroidal transformer with 7.5:1 ratio to match it better with the ef800.

Where did you get the trans from?
I think I will probably go the D-EF47 route because of tube availability. Maybe in the future I'll build another and try the D47 circuit.

 

[Purplenoise]

Where did you get the trans from?
I think I will probably go the D-EF47 route because of tube availability. Maybe in the future I'll build another and try the D47 circuit.

Got it from eBay but since it came from Russia he might not be selling now after the recent events. I have heard that you can still message him through eBay and get it though

 

[neowalla]

Build the one with the twin 6028 'if you like it hot'.
This microphone gets very hot, you can almost heat a room with it...
(A couple of years ago I have built this microphone for a friend.)

Ah, a "winter" microphone! Keep your booth nice and cozy! How is the self noise with this configuration?

 

[RuudNL]

How is the self noise with this configuration?

As far as I remember (it is already years ago), the self noise was 'reasonable', but not extremely low.
In fact I have never seen/heard a tube microphone that had a lower (or equal) self noise than a modern solid state microphone.

 

[neowalla]

I recently modded a T-11 with the "Fox 460" circuit from Microphone-parts. I don't have the wherewithal to really measure it, but in before/after recordings you can definitely hear the difference in self noise (among other things, of course). As tube mics go, I would say it's pretty quiet, but not as quiet as the S87 I built for sure. Still falls within ACX's -60 noise floor requirement though.

 

[kingkorg]

I have made a 47 with ef14, and it checks all the boxes.

 

[tomas.borgstrom]

I recommend building a U47 with EF12 point to point. The BV.08 transformers from Haufe, AMI or Moby are all great.

 

[Purplenoise]

Yeah ef12 and 14 work well…different flavours but both great nonetheless. I belong in the minority that prefer a nuvistor haha…13cw4 or 8393 for slightly less aggressive timbre.

 

[tomas.borgstrom]

I will soon make my schematic for U47 with EF12 public. I bias the tube differently than the other schematics I've seen. The timbre is less aggressive and to my ears it sounds extremely close to VF14.

 

[Purplenoise]

I will soon make my schematic for U47 with EF12 public. I bias the tube differently than the other schematics I've seen. The timbre is less aggressive and to my ears it sounds extremely close to VF14.

I’d be very interested to try it out

 

[neowalla]

I will soon make my schematic for U47 with EF12 public. I bias the tube differently than the other schematics I've seen. The timbre is less aggressive and to my ears it sounds extremely close to VF14.

I need to keep an eye out for that as well.

 

[tomas.borgstrom]

I'm about to make a homepage and I'll post it there with some background information. I'll make a thread here at the same time.

 

[benqbasic]

I'm about to make a homepage and I'll post it there with some background information. I'll make a thread here at the same time.

Very keen to see how you have biased the EF12. I have a build that i have played around with quite a bit.

 

[JW]

How different is EF13?

 

[mhelin]

EF13 is little bit different tube (remote cut-off variable mu pentode) but should work fine at VF14 operating point:
http://www.moxtone.com/mU47_U47_part3.html
EF13 adaptation with self bias:
http://www.moxtone.com/ConMic.html