MK47 PCB tube mic kit - build thread

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micaddict

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In76d wrote:

Yes, it's typical for 6028 - i don't know how those tubes can be considered as related to VF14.
Specs are different. Good that many folks like it, but is it anyway close to U47?
You readings are fine for 6028. There 's no option to get real U47 specs here.
For plate is correct, for polarisation - yes your multimeter input impedance is too low, for heaters - it should be a little underheating. 40V was a big underheating for VF14. To get similar result (in theory of course) for 6028 you should get around 13-14V :) I doubt that these tubes can work with that low heater voltage.

AFAIK the 6028 is basically a "hotter" version of the EF95 or 6AK5.

There's an 18AK5, too (Vf 18 Volts).
 

useme2305

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hey everyone,

i just read about putting the 1,5k resistor in the psu case in the aputis white market thread.

this of course is very easily achieved within this build with a 7 pin connector since we only need 5 pins for this mic.

my initial thought was to  simply make a roundtrip from mic to psu case via two cables and have the 1,5k resistor in the case.

but then i thought why not just put the resistor in the case, connect one end to the 105V source inside the psu and therefore only use one strand of the 7pin cable instead of two. this would be the right way to do it, right?

any cons that come with this solution? why was it not implemented in the original design of the MK47?
 

emrr

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Studio Mollan said:
I notice I have some electrical noise, sounds like ground hum, low but audible when in cardoid mode. Omni is dead quiet.
Anybody have any experience on this?
/
Emil

Did you find a reason?  Several reports in the full thread, seemingly different solutions in all cases.  I have one here doing the same. 
 

emrr

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Studio Mollan said:
I notice I have some electrical noise, sounds like ground hum, low but audible when in cardoid mode. Omni is dead quiet.

gevermil said:
exact same scenario here .

FIX:  ground pattern control line at PSU for cardioid rather than letting it float.  DPDT switch will let you wire it that way.  At least worked on this one. 
 

glimmertwins

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2nd request for archived versions of the information listed in the first post - photos, BOM, etc.  Looks like ioaudio's mailbox is full so can't message him via the private message feature. Thanks in advance!
 

ShaneSBG

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Potato Cakes said:
Does anyone still have the schematic and/or BOM for the PSU? It seems the links have been taken down on the original post.

Thanks!

Paul

This may be a bit late, but I have these...the first one was from Chunger, I'm assuming it's ok to put it up because I got it frome here. I have a couple more files I'll add also
 

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ShaneSBG

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Potato Cakes said:
Does anyone still have the schematic and/or BOM for the PSU? It seems the links have been taken down on the original post.

Thanks!

Paul

 

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ShaneSBG

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Potato Cakes said:
Does anyone still have the schematic and/or BOM for the PSU? It seems the links have been taken down on the original post.

Thanks!

Paul

Hope these help


 

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ShaneSBG

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Potato Cakes said:
Does anyone still have the schematic and/or BOM for the PSU? It seems the links have been taken down on the original post.

Thanks!

Paul

Here's a link to a page here also that was a big help for me when I built the D-47

https://groupdiy.com/index.php?topic=47112.60
 

ShaneSBG

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Potato Cakes said:
I appreciate the info!

Thanks!

Paul

Cool! Happy to help, I thought I had more, but that's all I can find. I tried to save as much info as I could when I built mine even though I built the other version
 

Potato Cakes

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I'm actually using this for a different U47 build, so the only thing I have left to sort out is resistors for a variable polarity pattern, but I may just get lazy and just use 3.

Thanks!

Paul
 

Potato Cakes

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Hello, everyone,

I just finished building the PSU and checked with the test load and after some tweaks to R4 I am able to get the B+ to 105V and everything thing is great. In the past I have used a 180k resistor for the test load that has always seemed fine, but using that here yields very high voltage like there is no load at all. Granted this has been mostly for C12/251 PSUs, but I' almost certain I have used it for a different U47 PSU before, but only almost. Is this just the properties of different PSUs interacting with different mics that need different testing methods? A dumb question, I know, and I'm pretty sure I know the answer. My inquiry mostly relates to learning the different methods for testing my builds and knowing that the readings I get are indeed correct and not marred by faulty procedures on my part.

Thanks!

Paul
 

Rixsta

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Can anyone tell me if the SCT700 microphone can only be used for the case/chassis for the MK47 or can parts of the power supply also be used ?
 

EvLoutonian

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Hi all,

I have a couple of questions..
I just completed a second MK47, using a PCB + transformer kit purchased mostly completed from a friend, and using an Equinox body & other parts I had purchased already when I first built one of these mic’s.

The second mic seems to have turned out pretty fine, but I’m noticing it registers 102v at the mic, using the power supply from the first mic, whereas the first mic registers just under 105v at the mic.

I visually inspected all components, and everything looks pretty much essentially identical between the two mic’s.

The only different is that in the first mic I used the Cathedral Pipes ‘Dale M7’ style capsule, whereas in the second mic I installed the Equinox Q-47 (K47 style) capsule.

So one question is, does the capsule itself effect the voltage I’m seeing at the mic, or should I be looking elsewhere?
(and does it matter if the second mic only sees 102v instead of 105v?)

I am yet to build the second power supply, so I can certainly adjust that to suit the second mic, but I’m just curious about whether both supplies should be compatible in the end, with both mic’s.

Also, I noticed the second mic seems to have lower overall  output level than the first one, seems like.

Is this likely to be due to the voltage, and / or different capsule?

Or perhaps another component?

Thanks!
Evan
 

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