MK-U47 - build thread

[andia]

MK-U47 is closer to original construction wise. If I remember correctly you could easily replace the 2 408s with original vf14 with just minor changes.

 

[Whoops]

MK-U47 has 2x 408 tubes..
See schematic on the top of the previous page..

Hi Martthie, the only think I remember from the MK47 project is that it used 2x 6028 tubes.

So it seems on this specific detail both the MK47 and MK-U47 projects used the same thing

Thanks

 

[JMc]

Hi. I think (hope) that I saved out that step-by-step build guide at some point . . . .
Lemme check for you.
Is there somewhere I can upload it on the forum?
(otherwise, just post me your email, and if I find it I'll forward it to you)

Cheers!
Evan

Hi Evan, that would be terrific if you still have it. You can e-mail me at [email protected] Thank you!!

 

[JW]

MK47 you had to source your own body, MKU47 I believe Max also produced (a badass) body for it. Nice in that it allowed you to do point to point or the two 408a's. You could also fit a bigger transformer in it if desired. I eventually put a Moby BV08 in my MK47 but that required some ugly shifting of things inside the body.

Anyway, I am very curious if anyone knows whether the original MK47 i/o audio transformer was different than the subsequent i/o audio MKU47 transformer.

I'm just speculating here, but remember the reports that the two 408a's output impedance isn't quite correct for the BV08? That ideally you might have slightly more step down (like 10:1)? Well I wonder if one of these transformers for the MK47 or MKU47 is doing just that. Maybe I'm remembering wrong and they're the same transformer though.

But I remember a long discussion with several people claiming a BV08 wasn't the right transformer for two 408a's. Max was insistent though that it was just fine.

Speculating again here, but when the MKU47 started selling it was advertised as more accurate. So, (that could mean?) the BV08 being wound at 6.5:1 or whatever the OG is. Is it possible the earlier MK47 had a higher step down ratio transformer?

 

[innercityman]

MK47 you had to source your own body, MKU47 I believe Max also produced (a badass) body for it. Nice in that it allowed you to do point to point or the two 408a's. You could also fit a bigger transformer in it if desired. I eventually put a Moby BV08 in my MK47 but that required some ugly shifting of things inside the body.

Anyway, I am very curious if anyone knows whether the original MK47 i/o audio transformer was different than the subsequent i/o audio MKU47 transformer.

I'm just speculating here, but remember the reports that the two 408a's output impedance isn't quite correct for the BV08? That ideally you might have slightly more step down (like 10:1)? Well I wonder if one of these transformers for the MK47 or MKU47 is doing just that. Maybe I'm remembering wrong and they're the same transformer though.

But I remember a long discussion with several people claiming a BV08 wasn't the right transformer for two 408a's. Max was insistent though that it was just fine.

Speculating again here, but when the MKU47 started selling it was advertised as more accurate. So, (that could mean?) the BV08 being wound at 6.5:1 or whatever the OG is. Is it possible the earlier MK47 had a higher step down ratio transformer?

Oliver Archtut's D-47 design with 2 x 408A (6028) tubes uses a BV08 transformer too.

 

[martthie_08]

I've recently acquired vintage Siemens / Halske 1uF capacitors that I would like to mount in my MK-U47.

These are the original bulky box type caps and I will somehow need to make room for them within the existing MK-U47 body.

The way I see it the upper elastic mounted plate with the tubes could be moved upwards another 0.8mm.

Would I run into any issues mounting the two caps on top of output transformer (instead of below) and sliding that entire assembly downwards?

That assembly could easily go down about 15mm once the 1uF / 0.5uF caps are out of the way.

This would also have the advantage of getting them away from the insanely hot 1k5 dropping resistor (the caps are rated at +70°C).

Any thoughts?

 

[Purplenoise]

I've recently acquired vintage Siemens / Halske 1uF capacitors that I would like to mount in my MK-U47.

These are the original bulky box type caps and I will somehow need to make room for them within the existing MK-U47 body.

The way I see it the upper elastic mounted plate with the tubes could be moved upwards another 0.8mm.

Would I run into any issues mounting the two caps on top of output transformer (instead of below) and sliding that entire assembly downwards?

That assembly could easily go down about 15mm once the 1uF / 0.5uF caps are out of the way.

This would also have the advantage of getting them away from the insanely hot 1k5 dropping resistor (the caps are rated at +70°C).

Any thoughts?

No problem at all. I’ve done it in one of my p2p 47s…both c2 and C3 caps above the transformer. Now if you have to modify the pcb be careful not to ruin any traces.

 

[Bonnie1]

Oliver Archtut's D-47 design with 2 x 408A (6028) tubes uses a BV08 transformer too.

Just for accuracy, Oliver did not design the D-47. Oliver never designed a tube mic circuit utilizing 2 x valves

 

[innercityman]

Just for accuracy, Oliver did not design the D-47. Oliver never designed a tube mic circuit utilizing 2 x valves

So you pretend that the informations on this page are false, and by the way, dany Bouchard would be a liar ? check this...
https://www.vintagemicrophonepcbkit.com/D-47.html

 

[martthie_08]

No problem at all. I’ve done it in one of my p2p 47s…both c2 and C3 caps above the transformer. Now if you have to modify the pcb be careful not to ruin any traces.

that's great to hear thanks!

Back when building the mic I believed the capsule had to sit somewhere in the middle of the head basket beneath the cross-bar. Looking at pictures from original units it seems the capsule sits much higher in the head basket, having the cross-bar pretty much covering a bit of the upper part of the capsule. This is another part in the puzzle I would like to correct.
Would someone have any capsule - spacers left over they'd be willing to sell and send me?

 

[Purplenoise]

that's great to hear thanks!

Back when building the mic I believed the capsule had to sit somewhere in the middle of the head basket beneath the cross-bar. Looking at pictures from original units it seems the capsule sits much higher in the head basket, having the cross-bar pretty much covering a bit of the upper part of the capsule. This is another part in the puzzle I would like to correct.
Would someone have any capsule - spacers left over they'd be willing to sell and send me?

Studio 939 has spacers I believe. If not I use regular stand offs for pcb mounting. Doesn’t look really pro but it gets the job done.

 

[martthie_08]

Studio 939 has spacers I believe. If not I use regular stand offs for pcb mounting. Doesn’t look really pro but it gets the job done.

thanks! they have two 8mm versions (only the simple one available atm), I will see whether that's a good fit!

 

[benqbasic]

So you pretend that the informations on this page are false, and by the way, dany Bouchard would be a liar ? check this...
https://www.vintagemicrophonepcbkit.com/D-47.html

You said that Oliver designed the D-47......Oliver Archtut's D-47 design with 2 x 408A (6028) tubes uses a BV08 transformer too.

Oliver talked about using 2 tubes in parallel but to my knowledge he didn't design any mics with parallel tubes and he didn't design the D-47. The D-47 is basically a copy of the MK47 by ioaudio.

 

[wlinart]

reminded me of this thread: IOaudio Inventor of the parrallel 408a tube configuration in U47 Clone ?

 

[innercityman]

You said that Oliver designed the D-47......Oliver Archtut's D-47 design with 2 x 408A (6028) tubes uses a BV08 transformer too.

Oliver talked about using 2 tubes in parallel but to my knowledge he didn't design any mics with parallel tubes and he didn't design the D-47. The D-47 is basically a copy of the MK47 by ioaudio.

I've noticed that the D-47 was a copy of the MK-47 from Max as I've built one last year, bought it on the black market from a guy who gave up building it up. so thanks for this information as I was not really sure. I've just relayed an information I've read on Dany's shop page. I don't mean to pretend anything.

 

[innercityman]

And by the way... does someone know why Max (iOAudio) has stopped selling MK-47 and MK-U47 kits ? Did he passed away too ? That's a shame that the only chance to get one of that kit is from a guy who never built it up. I've been lucky last year, I love mine, and would love to build a second one.

 

[Gus]

innercityman
That is a good question
I have not seen an iOAudio post for years.

 

[wlinart]

i think he's too busy making and selling his tlm67 retrofit kits.
Introducing the fabolous TLM67/U87 to U67 mod | Realgearonline

 

[Whoops]

i think he's too busy making and selling his tlm67 retrofit kits.
Introducing the fabolous TLM67/U87 to U67 mod | Realgearonline

That thread has no follow ups after 2017,
Max is more active in the Gearslutz thread, it has pictures also:

https://gearspace.com/board/product...6-introducing-fabolous-tlm67-u87-u67-mod.html

 

[innercityman]

That thread has no follow ups after 2017,
Max is more active in the Gearslutz thread, it has pictures also:

https://gearspace.com/board/product...6-introducing-fabolous-tlm67-u87-u67-mod.html

this thread on Gearspace is from 2014