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Author Topic: Fred Cameron U67  (Read 12905 times)

Bdub

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Fred Cameron U67
« on: October 14, 2013, 08:29:55 PM »

I have a U67 modded by Fred Cameron in Nashville. "Modded" might the wrong word- Fred replaced the electronics and the power supply. The mic sounds very good to me.

Unfortunately, we had a bit of flooding in the studio, and the mic's power supply got wet. None of the electronics were submerged, as they are mounted to the top of the case, but there was water in the bottom of the case.

I immediately removed the bottom panel and fan dried the power supply for a few days. Then the mic was set aside, as we rectified the water damage to the studio.

I tried the mic for the first time today, and the power supply lit up, but there was no sound from the mic.

I opened the power supply and discovered that some corrosion had taken place, and the copper wire in the transformer had opened. it had literally come apart.

Fred passed away some time ago, and there no longer seems to be a "Cameron Labs in Nashville.

Does anyone know of someone who could resurrect this power supply?

I'm really sick about this- it's my favorite vocal mic, and I'm in the middle of two projects that were using it.

Thanks for reading.
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soapfoot

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Re: Fred Cameron U67
« Reply #1 on: October 14, 2013, 10:12:00 PM »

What is the secondary voltage of the power transformer? Does it have a make and model listed?

If not an off-the-shelf part (likely) then you might have to get a custom one made, but this is not impossible.

As long as the mic itself is safe, any good tech should be able to repair your power supply.
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Bdub

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Re: Fred Cameron U67
« Reply #2 on: October 15, 2013, 09:44:54 AM »

Yes, the mic itself is safe. I will take another look at the transformer when I get home tonight, and post what I find.

Thanks for the reply!

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Bdub

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Re: Fred Cameron U67
« Reply #3 on: October 16, 2013, 11:34:20 AM »

Okay.
The transformer primary shows a few ohms on the meter, so it's not open.
The secondary, however, shows open on all three connections, in any combination.

With power applied to the primary, the secondary outputs nothing, so I think I have an open secondary.

I'll post a couple of pictures this evening.
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soapfoot

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Re: Fred Cameron U67
« Reply #4 on: October 16, 2013, 12:04:53 PM »

This is as expected. You've identified your problem.

Next step-- figure out the spec of the transformer and replace it (either with an off-the-shelf part or a custom wound replacement).

Power supplies are much less esoteric than what goes on inside the microphone itself-- the supply is a fairly simple animal in most cases (there are exceptions). Any good tech is qualified to repair a simple power supply.

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Bdub

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Re: Fred Cameron U67
« Reply #5 on: October 16, 2013, 12:20:58 PM »

Any recommendations? I know Klaus is up to his nose in work for the forseeable future.
(I've lurked here for years, and  used to post under my real first name.)

I don't have the expertise to deduce the specs of a transformer from the circuit it's in.
This looks like a one-off built from scratch to me, although it has a circuit board.

I'm in the southeastern Michigan area, near Detroit, but I'll consider damn near anyone, anywhere, you think could figure it out.

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klaus

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Re: Fred Cameron U67
« Reply #6 on: October 16, 2013, 12:59:38 PM »

Please remove the transformer from the power supply, and post a couple of close-up pictures from several sides. There are not that many tube mic transformer manufacturers that it would not be fairly easy to identify the manufacturer from the pictures.

Then you contact the manufacturer and forward these pictures. At worst, you can give the manufacturer the required DC output voltage and current specs: (+) 210VDC, 0.88mA  (-) 6.3VDC , 200mA. That way, they can match them in their replacement trafo.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Bdub

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Re: Fred Cameron U67
« Reply #7 on: October 17, 2013, 09:05:04 AM »

I wasn't able to dismount the transformer yet, but perhaps these pictures will help.
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Bdub

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Re: Fred Cameron U67
« Reply #8 on: October 17, 2013, 09:06:07 AM »

Connection Side.
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Bdub

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Re: Fred Cameron U67
« Reply #9 on: October 17, 2013, 09:21:34 AM »

Top view, showing layout.
Primary is top, secondary is bottom.
Visible numbers are "772".
Other numbers are obscured by deteriorated foam that is stuck to the top.
Any suggestions on how to remove it without removing the numbers underneath are most welcome.
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Bdub

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Re: Fred Cameron U67
« Reply #10 on: October 17, 2013, 09:24:47 AM »

XFMR Primary Side.
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Bdub

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Re: Fred Cameron U67
« Reply #11 on: October 17, 2013, 09:26:21 AM »

XFMR Secondary side.
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Bdub

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Re: Fred Cameron U67
« Reply #12 on: October 17, 2013, 09:27:29 AM »

XFMR Top View. Primary down, secondary up.
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Bdub

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Re: Fred Cameron U67
« Reply #13 on: October 17, 2013, 09:32:37 AM »

Just to note, this mod replaced all the circuitry inside the mic itself with what appears to be a very simple tube circuit. Even the mic's Tuchel connector was replaced with a multipin XLR.

I'll post pics of the inside of the mic in a day or two.

Thanks, Klaus, for that info. Do you think the fact the mic is using a different tube (12ax7) would affect the voltages you provided?
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soapfoot

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Re: Fred Cameron U67
« Reply #14 on: October 17, 2013, 10:02:29 AM »

I can't tell much about the transformer from the pictures, but it appears to have multiple primary configurations at least, which hints to me that it's likely an off-the-shelf part. Nothing in this PSU looks particularly custom or esoteric, though in my personal opinion I would've hoped to see greater care in its construction.

I know you didn't ask for this opinion, but since the PSU will require a rebuild anyway, perhaps now would be an appropriate time to at least pause and consider converting the microphone back into a true U67?  I'm not familiar with Mr. Cameron's work, but in my opinion it would be hard to improve on Neumann's original design. If it has the original capsule and BV No. 12 transformer, then it could probably be restored and paired with a new, professionally built power supply. You would lose remote pattern control, but would have an iconic, historic microphone.

However, you may enjoy the microphone in its current form-- if you've compared to an original U67 and prefer its performance, then by all means carry on.
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