U47 second mic build first U47

[Pip]

ln76d
Thinking about building casuals my thing was building the Mylar  gold sputtering was what I didn't have the equipment. I can always get a small metal lathe. I have the specs on the capsule hole location. not top secret. I think I still have them I will look. I'm not sure where I got them. 

-Larry

I don't know if a small lathe is going to give you the accuracy you need to attain for capsules of consistent quality. That is why so many manufacturers job out the heavy milling and then do the fine tooling in-house. I too am interested in the spec's you have if it is not a problem. Especially as pertains to lapping, tension and screw torque and sequence.

 

[wilberweb]

Hi, PIP
I'm looking for the paper work on the capsule. It has hole spacing dimensions size of holes. I just seen it a few weeks ago.
I am looking for it. I think that a lathe should be able to handle it. I'm not sure who to get to make the capsules. and Gold sputtering.

-Larry

 

[wilberweb]

Here is what I have on the capsule diagrams and specs

 

[wilberweb]

second picture

 

[wilberweb]

Here is the pdf link to the file online http://www.sdiy.org/oid/ldc/Debenham-StereoCondenser.pdf

 

[wilberweb]

A good source of pdf mic information http://www.sdiy.org/oid/ldc/RWilliamsonMic.pdf

http://www.sdiy.org/oid/ldc/Debenham-StereoCondenser.pdf

http://www.sdiy.org/oid/ldc/RSchulein.pdf

http://www.sdiy.org/oid/ribbon/BantamVelocityMicrophone.pdf

http://www.sdiy.org/oid/ribbon/MakeThisRibbonMic.pdf

 

[wilberweb]

All finished with my U47 Mic build works awesome.
Thanks Dan at vintage mics http://www.vintagemicrophonepcbkit.com/
and Chunger at http://store.studio939.com/product/budget-47-body-kit. Advance Audio microphones http://advancedaudio.ca/
and collective Cases http://collectivecases.com/?product=psu-cases.

 

[micaddict]

Congrats!

Enjoy. 

 

[wilberweb]

Thanks Micaddict 

 

[901]

I just finished the build of a vintage-mic.com U47 kit. Unfortunately I have some difficulties to make it work.

When I connected the audio and tried the mic out I had to crank the gain on the mic preamp and my voice sounded thin. There was a whole lot of crackle also.

So I had the suspicion, that there is something wrong with the high voltage or the ground. I checked every connection and then dug out the data sheet for the EF80 tube. I measured the plate voltage directly on the tube socket  and got something below 50V while the power supply measured 105V!
Strangely enough when I switch the psu on, the voltage on the tube goes rapidly up to ~100V as expected, but after a few seconds goes down to below 50V.

What could be the problem? There are no capacitors on the mic that would take seconds to load or unload. The voltage on the psu doesn't change.

 

[ln76d]

What could be the problem?

vintage-mic.com

 

[ln76d]

Anyway max. input voltage on plate for few seconds is normal.
That's why many tube gears have stand-by switch, especially power amps.

 

[Matt Nolan]

I just finished the build of a vintage-mic.com U47 kit. Unfortunately I have some difficulties to make it work.

When I connected the audio and tried the mic out I had to crank the gain on the mic preamp and my voice sounded thin. There was a whole lot of crackle also.

So I had the suspicion, that there is something wrong with the high voltage or the ground. I checked every connection and then dug out the data sheet for the EF80 tube. I measured the plate voltage directly on the tube socket  and got something below 50V while the power supply measured 105V!
Strangely enough when I switch the psu on, the voltage on the tube goes rapidly up to ~100V as expected, but after a few seconds goes down to below 50V.

What could be the problem? There are no capacitors on the mic that would take seconds to load or unload. The voltage on the psu doesn't change.

I'm not familiar with that kit, but that sounds about correct behaviour to me. Most plate loaded valve mics set the anode to roughly half of the supply rail. It is close to 100V at the beginning because the valve has not warmed up and is not yet conducting - it is a much larger resistance than the anode resistor.

I think your problems are elsewhere. Check the capsule polarisation. Check the transformer wiring.

 

[901]

Thanks for the hint! Meanwhile I have found the problem. The negative signal wire looked like it was firmly tightened to terminal block, but wasn't.

I also got pointed to this thread:
http://groupdiy.com/index.php?topic=56878.0

So the plate voltage is really correct. Being a guitar player I'm more used to plate voltages almost ten times higher and couldn't imagine that about 50V could be intentional.

Thanks again!