synthiaks

U47 question
« on: March 11, 2020, 06:39:37 AM »
We just got an U47 from a friend who lent it to us for use in our studio, its an old 50s one with a serial around 180. "Better being used than in a safe" was his comment. It has an VF14 in it and I'm just not sure how to deal with this. What kind of a life span do this tube have ? And should we even use it?

Its worth soooo much money and we don't record Frank Sinatras at our place (Post production)

Maybe the tube guys here can give some feedback on this "problem"

The friend also sent us a CMV3!?


S
"ex observer in silence"


Murdock

Re: U47 question
« Reply #1 on: March 11, 2020, 07:41:59 AM »
I don't understand what the problem is?  ::)
Are you afraid of using it because of the high price?
Do you have the original power supply?

Re: U47 question
« Reply #2 on: March 11, 2020, 07:56:43 AM »
Hi,
if it hasn't been used since a long period, i wouldn't just plug it without checking first:

-all diodes and all the coupling and filtering capacitors in the psu and mic (esr meter)
-then check and set the PSU HT voltage with dummy load resistor  (120v output).
-then check the heater voltage with a dummy load in place of the vf14 tube (35v).
-check the value of the R7 R8 resistors (1M and 2Mohms)
-clean all the HiZ parts (resistors, caps, polar switch) with care (diluted isopropyl alcool), the connectors as well.
-the shape of the capsule membranes , and all the solder joints
-plug the vf14 and check the voltages at plate and cathode.

http://www.sdiy.org/oid/mics/Neumann-u47.gif

that could be a good start
Regards
Fred
« Last Edit: March 11, 2020, 08:02:42 AM by granger.frederic »

Pip

Re: U47 question
« Reply #3 on: March 11, 2020, 03:33:27 PM »
Yes it would be bad if the tube died on your watch, I personally would be very reluctant to be responsible for somethin that wasn't mine and was as valuable as that,  but,  "better used than in a safe".

Ask the owner what they think and move on.
Pip
New York City
http://geosonixlab.com

synthiaks

Re: U47 question
« Reply #4 on: March 11, 2020, 05:24:08 PM »
I don't understand what the problem is?  ::)
Are you afraid of using it because of the high price?
Do you have the original power supply?

Probem being the VF14, in a safe it would get NO hours of usage, in our studio probably more. So what kind of lifespan does the VF14 have?  When its gone, its gone and will never be replaced by one as they are near extinct.

This mic was Serviced
"ex observer in silence"

Re: U47 question
« Reply #5 on: March 11, 2020, 05:55:03 PM »
thanks to the underheating design, the VF14 could last a lifetime ...
depends on how the mic was used before.

synthiaks

Re: U47 question
« Reply #6 on: March 12, 2020, 03:26:09 AM »
thanks to the underheating design, the VF14 could last a lifetime ...
depends on how the mic was used before.

Thank's

The whole "usage until now" is a blackbox but this is what i wanted to know.

S
"ex observer in silence"

gyraf

Re: U47 question
« Reply #7 on: March 12, 2020, 08:05:47 AM »
My own u47 had a capsule repair and a prophylactic tube change by Neumann Berlin around 1995 - it has been in use - if not every day then at least a couple of times a week - ever since

Now slightly dented because someone used it to hold open a door so that their guitar cable did not get caught in it  ::) - but no other signs of wear. I think the VF14's lasts a very long time, the other u47 in our studio was never serviced while we have had it (1988?) and holds up as well..

So I think you should use it and see if you like it, it's a waste locking it away. Yes, there is a statistical chance of failure, but such is life - and the owner probably is/should be aware of that.

Frederic's post above should get it started in the safest possible way..

/Jakob E.
..note to self: don't let Harman run your company..

rockinrob86

Re: U47 question
« Reply #8 on: March 12, 2020, 11:19:02 AM »
The tube will last if nothing happens to it.  The main culprits for damage I would worry about would be the power supply and the mic cable.  Don’t wheel over the cable, avoid stepping on it - be good to it.

The power supply needs to be serviced and maintained.  They need fresh electrolytic capacitors every 20 years or so.  Use a good power source, with some overvoltage protection.  Power strips go bad - the MOVs in them wear out and stop offering protection at some point.

That stuff is maybe a bit paranoid, but it is a $10k mic.  The capsule may or may not already be bad, but there isn’t anything you can do about that.  Keep the mic stored in the box with fresh silica packets.

Use a good atlas or latch lake stand with it.

Otherwise, it’s a tool.  It won’t bite you!

Re: U47 question
« Reply #9 on: March 12, 2020, 11:47:21 AM »
Changing parts in high value historical mics, like an U47, could decrease their reselling price...
i would test the capacitors with an ESR meter first, before changing them.
Inspecting the capsule is important , if you have a loose diaphragm (do the breath and plosive test) or cracks (M7 with pvc) , i wouldn't put it , for example, in front of a powerful amp...
« Last Edit: March 12, 2020, 05:31:30 PM by granger.frederic »


synthiaks

Re: U47 question
« Reply #10 on: March 13, 2020, 02:49:36 PM »
Thank you all for the answers!

I was just unsure but feel more secure now.

The microphone was restored here in Berlin by Andreas Grosser so  i guess the Electronics are all good.

Looking forward to test this baby!

S
"ex observer in silence"


 

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