Murdock

Re: MK47 PCB tube mic kit - build thread
« Reply #1420 on: April 21, 2019, 02:51:59 PM »
and does it matter if the second mic only sees 102v instead of 105v?


I would not worry about 3v difference. Each tube draws different amount of current, so that's probably where the 3v come from. That's also why you should keep power supplies with there respective microphones. So you set up the correct voltage for that particular tube/mic once and leave it (except for checking it every few months) until you change the tube again.
Concerning the gain difference; that could also be the tube. Maybe swap the tubes and see if the gain changes with it.
« Last Edit: April 21, 2019, 03:27:32 PM by Murdock »


Re: MK47 PCB tube mic kit - build thread
« Reply #1421 on: April 21, 2019, 09:14:39 PM »
Ok, cool - and thanks for the suggestion on trying different valves - I have some spares I can also try.

Re: MK47 PCB tube mic kit - build thread
« Reply #1422 on: April 21, 2019, 09:17:24 PM »
Overview of the two MK47’s

Pip

Re: MK47 PCB tube mic kit - build thread
« Reply #1423 on: April 21, 2019, 11:38:25 PM »
I would not bring those two wires through the transformer bobbins like that. Seems like a good way to induce voltage where you might not want it.

I would not worry about the gain difference unless its drastically different. All the things others have said is true in my experience with this mic design. The 408a tubes vary greatly in their noise floor and sonic quality, I tested dozens before I settled on two tubes that I liked the sound of.

As to the power supply that is suggested for this mic remember it is an unregulated design so therefore the voltage will change with varying states such as line voltage fluctuation and component variance.

Lastly those are drastically different capsules and it does not surprise me at all that the mics vary in voicing and timbre.
Check out this awesome website for some real testing and data on the mic that inspired this design.

http://www.moxtone.com/mU47_U47.html
« Last Edit: April 26, 2019, 12:38:08 PM by Pip »
Pip
New York City
http://geosonixlab.com

Re: MK47 PCB tube mic kit - build thread
« Reply #1424 on: June 03, 2019, 06:42:44 PM »
Hello fellows,

I built an MK47 5 years ago. It worked perfectly and sounded amazing until the beginning of this year, as it just died suddenly.  We examined it with a local tube electronics guru and didn't find any faults in the PSU or the mic. Suddenly it worked fine again, until going silent again after few days. My friend started to test it and while holding the mic in his hand got a massive electric shock in his arm turning the power on... and a few seconds later another one in the arm holding the mic body. He had dizziness and aching arms for few days but was lucky to survive alive. The only damage I can find are those burnt legs of the USSR capacitor.

Pip

Re: MK47 PCB tube mic kit - build thread
« Reply #1425 on: August 05, 2019, 12:03:42 PM »
Hello fellows,

I built an MK47 5 years ago. It worked perfectly and sounded amazing until the beginning of this year, as it just died suddenly.  We examined it with a local tube electronics guru and didn't find any faults in the PSU or the mic. Suddenly it worked fine again, until going silent again after few days. My friend started to test it and while holding the mic in his hand got a massive electric shock in his arm turning the power on... and a few seconds later another one in the arm holding the mic body. He had dizziness and aching arms for few days but was lucky to survive alive. The only damage I can find are those burnt legs of the USSR capacitor.

The fuse didn't blow? Please check that the ground is intact through-out the whole circuit. The body of the mic should never have been able to get energized without the fuse in the PSU blowing. Your friend is very fortunate.

That cap is the output cap yes so if it failed or the solder connection failed that would explain the no output and possibly how the body was energized but again the fuse should have blown.
Pip
New York City
http://geosonixlab.com


 

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