wa 47

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Gus

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The WA67 thread made me curious about the WA47. I searched and it has a 5751 tube.
I seem to remember reading on the web 20 years ago or so that the SPA adjusted 47s could have a 5751 in them.
I found some pictures on the webs that I might be able to reverse most of the wa schematic from.

Has anyone traced it yet?

EDIT found this reply 536 is interesting
Warm Audio Introduces WA-47 Tube Condenser Microphone - Page 18 - Gearspace.com
 
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soapfoot

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The part of that I find most confusing is the reference to “taking off the PCB solder mask” as though there were some unnamed objective for doing so—and in context, it even seems to imply a sonic objective?
 

Flatpicker

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I have one of these and planned to trace the circuit and post about it at some point (inspired by Whoops’ WA-67 thread), but just haven’t got there yet. This guy Chad Kelly sells mods for these and I think he used to do design work for WA. Here’s his website: Home | Signal Art Electronics

He’s got some interesting info on there about the development of the 47 regarding how WA left some things undone that they should have tidied up prior to the final release. Apparently the '67 got the same treatment.

He further explains that, while not an actual U47 circuit (of course) it does a decent job, and even better with a tube and cap upgrade.

Anyway, for starters I was planning to swap out the tube with a TAD 5751 and replace the output coupling 1.8uF cap with a better 1.5uF that will fit in there.

I hadn't seen the Gearspace thread - I'll give it a read.
 

Gus

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Is it based off the China microphone circuits like the Apex 460?
 

rock soderstrom

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Is it based off the China microphone circuits like the Apex 460?
It seems so, kidvybes about the Alctron MK47:

"...yes, both Art and Apex are Yorkville brands, and the T4 appears to be a re-packaged Alctron MK47...the circuit in the MK47 is the same as in the Apex 460...the capsule is a 35mm K67 rather than the 460's 32mm K67...the T4 is an excellent candidate for modding,

...a lot of the modders/DIY builders are using the Alctron MK47 body to build custom 47-inspired mics...Brian does that as well...I have an Ioaudio MK-47 U47-recreation built using the same body/headbasket:
http://store.studio939.com/product/m...phone-body-kit

...I've noticed this mic by the Hamiltone Guitar Co. on eBay lately, which also appears to be a rebranded Alctron MK47...not sure if they further modify it, but at that pricepoint I would hope so:
http://www.ebay.com/itm/Hamiltone-H4...-/191636016071
"


from your link, gearslut cdkelly about the role model of the WA47:

"As for how the mic was 'designed', it was not designed for a 5751. It is largely based on an Asian mic that has been on the market in China for many years called the Alctron MK47. Those mics have always shipped with a Chinese 7025 (mil spec 12AX7), and that's what it is 'designed' for. The work we did at Warm was merely to import this mic and re-work the PCB layout to reduce noise and improve sonics as much as humanly possible (putting in a much better transformer, better tube, better capsule, upgrading component quality, tweaking the voicing, taking off the PCB solder mask and moving around some stuff on the boards, etc; but the inherent 'design' itself never changed. At the heart of it, its still the Asian 12AX7 circuit that we found."

Here is the original Alctron MK47

 

Gus

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Has anyone seen a schematic of a SPA mod of the U47 with a 5751

Found this listing

EDIT
If you look at the pictures it looks like one triode has the plate, grid and cathode connected and is not used
Has the transformer been rewired for a different ratio?
or
has something else that I can't see be done with the circuit
 
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Flatpicker

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I just finished tracing the circuit and what do you know, lol!

EDIT: I didn't put the transformer ratio on the drawing, but I would assume that it is 6:1.

EDIT#2: I originally mistakenly crossed out R3, but it is on there. Also forgot to make C7 1000pF.

'47.jpg
 
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Flatpicker

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Here's an interesting tid-bit of info - the TAD 5751 datasheet says "The TAD™ 5751 is not suited for cathode follower applications due to a low cathode to heater max design voltage." Hmmmmmmm.....


Edit: I just happened to check the cathode to heater voltage spec and it's 90V (don't know why I didn't check that when I wrote the post - my brain just gets ahead of itself). Anyway, the TAD or any other 5751 should be plenty fine in this circuit.
 
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Papa Tango Charlie

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Je viens de finir de tracer le circuit et que savez-vous, lol !

EDIT : Je n'ai pas mis le rapport du transformateur sur le dessin, mais je suppose qu'il est de 6:1.

EDIT # 2: j'ai à l'origine barré par erreur R3, mais c'est là-dessus. Aussi oublié de faire C7 1000pF.

View attachment 91073
Bonjour
Je viens de finir de tracer le circuit et que savez-vous, lol !

EDIT : Je n'ai pas mis le rapport du transformateur sur le dessin, mais je suppose qu'il est de 6:1.

EDIT # 2: j'ai à l'origine barré par erreur R3, mais c'est là-dessus. Aussi oublié de faire C7 1000pF.

View attachment 91073
Bonjour
Je viens de finir de tracer le circuit et que savez-vous, lol !

EDIT : Je n'ai pas mis le rapport du transformateur sur le dessin, mais je suppose qu'il est de 6:1.

EDIT # 2: j'ai à l'origine barré par erreur R3, mais c'est là-dessus. Aussi oublié de faire C7 1000pF.

View attachment 91073

Hello is it the ultimate schematic for the WA47 Apex mod? Is there any other modification to bring to this schematic to build the WA47?
 

Papa Tango Charlie

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I have never tested the apex tranformer but it seems that most of Tbone and chinese tubes microphones are 5:1 from what i have heard? Does anybody have a idea of what is the ratio the Apex microphone transformer?
 

Flatpicker

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This isn't a "mod" but rather my interpretation of the circuit. The main differences from the stock APX 460 are the tube, output cap, transformer and capsule, and you can get all the available info regarding these from the WA website. They don't spec a ratio for the transformer, but I'd bet an AMI 6:1 would do the trick.
 
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Papa Tango Charlie

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Apparently the original transformer is a 11.6:1. If anybody has more information about mod the Apex 460 into a beautiful silky 47 microphone welcome i would like to learn more about it. Thanks to yall
 

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