MK7 - tube mic project

[ChuckD]

OK

Thanks,

Can you tell me why the glass tubes in the design? For the through holes it looks like. But why is glass used for this purpose?

-Chuck

 

[rodabod]

Glass is an excellent insulator.

 

[ioaudio]

RE: the grille.

yesterday i made some measurements from a u47 pic - someone with a real u47 and some spare time is welcome to correct my findings.

i have a m147 head basket, and it seems they used the same types of wire mesh, but the other way round ( thickest diameter inside)
while comparing the m147 grille with the cheaper build i learned that the mesh material is a lot stiffer. i remember that from building the g7 mic housings - i invested in the wrong assumption that i needed brass, without specifying the quality. i found some very nice material locally, never asking what exactly the material is.
tin-bronce (phosphor bronze) is a little darker, also non-magnetic, but stiffer at the same diameter.
brass is softer and needs thicker wires for the same mesh width, resulting in a lower percentage of open area.

edit: waiting for data regarding the wire mesh sizes. see als this thread:
http://www.groupdiy.com/index.php?topic=30742.0

 

[e.oelberg]

round the corner of my studio is the manufacture who did the galvanization for neumann since the 50ies. I could ask how the grill was galvanized

nicholas

 

[Martin B. Kantola]

You will want the "chrome" finish, no? It seems to sound better... To me it looks like the wire is different diameter.

Martin

 

[Gus]

I wonder if the outside mesh angle was part of the design for strength being at an angle.  Would it take more to crush with the angle and does the head grill ring different when tapped? 

 

[ioaudio]

it seems they used 2 diameters for the outside layer - a thicker one for the chrome?
again, i can do only guesswork from pics...

 

[Gus]

Max I just tried to measure my nady 1050 grill. The top dome section is two layer and the side is three layer.

The outside measurement of the outside mesh square was about 2.77mm outside to outside, it moves and is kind of hard to get a good measurement
The inside of the square measures about 1.26mm again it moves

The wire dia measured .69mm

The numbers don't sum, .69mm plus .69mm plus 1.26mm = 2.64mm not 2.77mm: However if you subtract .69mm it is about 2mm. So maybe the china stuff is close.

The important measurement might be the smaller mesh, Short of taking apart the grill and measuring the mesh most of this is a guess.

I guess the best way would be a CJ on a real 47 grill and a China grill that looks close.

 

[ioaudio]

a good way to measure it is to make a macro picture, very close up with some light from the bottom.
here is the dome of a m147:

 

[FerrariT]

I guess the best way would be a CJ on a real 47 grill and a China grill that looks close.

;D HAHAHA!

great idea very doubtful though. that would be an investment of sorts, no?

 

[ioaudio]

here´s a suggestion for the "passive" psu
the choke used is the Triad C-40X, available at allied

 

[bradb]

Are there any updates to the USA / NA BOM?

any things to be aware of?

 

[Jonkan]

Can someone do me a favour and measure the slot in the rubber shockmount where the capsule mounts on the sc700t mic? I want to send some measurements to a friend who is helping me machining some capsule mounts for this.

Thanks!
/J

 

[bradb]

I'm doing some research here on prodigy about the PSU.. Some others who were building dual psus for G7s were told that they should make a double PSU instead of building one to handle 2 mics.

Surely we can get a single toroidal tranny in there to supply two individual psu boards?  What VA rating would they need?

 

[ioaudio]

for a LDC i would suggest to build one psu/mic. there will be a situation when you want to use them on different locations.

the slot in the rubber mount is 7,8mm x 1,9 mm with a m3 thread.

 

[Arno]

Thanks alot max

Two more questions for the psu:

How do we get 160V?
12V from the heater into a reversed 18V mains transformer will give 153V. into a primaries-paralleled 35V transfo gives 157V
Is that close enough ??


Ican't find the wirewound 22R 5w pot.
other - much higher values i can find but cost more than an m7 capsule


gr
arno

 

[ioaudio]

back to back transformers often give different voltages than the calculated ones. try/error.
or order a costum wound transformer with the specs given.

the poti can be found here:
http://www.elektronikbauteile.de/index.html?bauelemente_passive_potis,_trimmer_drahtpotis_mit_6mm_achse.htm

 

[bradb]

i smell a group buy on a toroid!

 

[zebra50]

My progress so far with ioaudio's kit....

;D

 

[natek]

maaaaan nice use of the old vintage body! I like the end bell!