Topic: Fred Cameron U67 (Read 14082 times)

Bdub · « **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.

soapfoot · « **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.

Bdub · « **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!

Bdub · « **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.

soapfoot · « **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.

Bdub · « **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.

klaus · « **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.

Bdub · « **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.

Bdub · « **Reply #8 on:** October 17, 2013, 09:06:07 AM »

Connection Side.

Bdub · « **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.

Bdub · « **Reply #10 on:** October 17, 2013, 09:24:47 AM »

XFMR Primary Side.

Bdub · « **Reply #11 on:** October 17, 2013, 09:26:21 AM »

XFMR Secondary side.

Bdub · « **Reply #12 on:** October 17, 2013, 09:27:29 AM »

XFMR Top View. Primary down, secondary up.

Bdub · « **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?

soapfoot · « **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.

Kai · « **Reply #15 on:** October 17, 2013, 11:25:35 AM »

Looking at your pictures I would suggest:
Forget about this PSU, it's dangrous to use it.
It has been dangerous before it drowned, and it's even more now.

Get yourself a proper built PSU.
These are availale e.g. from Peluso and others at affordable prizes.

Regards
Kai

Jim Williams · « **Reply #16 on:** October 17, 2013, 11:39:51 AM »

There are small, off the shelf Triad and Stancor power transformers with a high voltage tap and 6.3V heater taps. Look them up in a Digi-key or Mouser catalog on-line.

That is one scary looking high voltage power supply. Definatly not "UL Approved".

soapfoot · « **Reply #17 on:** October 17, 2013, 12:04:15 PM »

Agreed with both of the above.

klaus · « **Reply #18 on:** October 17, 2013, 02:35:35 PM »

Quote from: Bdub on October 17, 2013, 09:32:37 AM

(...) Do you think the fact the mic is using a different tube (12ax7) would affect the voltages you provided?

Dual-triod 12AX7, when used in mics, have a positive heater voltage applied. The U67's EF86 penthode was biased via a negative heater voltage. While the transformer's current and voltage specs may be similar for both tube types, the power supply cannot be used for a stock U67 with EF86 as currently conceived.

I concur with several previous posts: the build-quality of the supply is not confidence-inspiring. The advantage of the Cameron mod, whatever its subjective sonic strengths may have been, does not outweigh the disadvantage of a badly built power supply with potentially lethal voltages. If the mic can easily be restored to its original, stock, circuitry, I would stop the bleeding and buy a decent, high-quality power supply, and restore the whole system to stock-original Neumann performance.

Bdub · « **Reply #19 on:** October 22, 2013, 01:10:26 PM »

Thanks for all the replies and information.

I agree with everyone.

In Fred's defense, I was told this was one of his first mods, and to me it looks like possibly some "prototyping" was going on.

Now I have to decide if I want to try rebuilding this myself (I have some electronics background and have successfully built or repaired some tube gear in the past), or get someone else to do it ($$$). Actually, maybe ($$$$).

I've been looking at Joseph Gyraf's G7 tube mic build- could his circuit be used for the 67 capsule? I know his circuit was intended for a CK12, but he talks about a change to accommodate other capsules on his page.

http://www.gyraf.dk/gy_pd/g7/gic.htm

I'm not averse to starting with the capsule and mic body, and rebuilding everything from there.

Since the insides of the mic were replaced, I would have to find the original Neumann "guts" to restore this to a real U67, wouldn't I? Isn't that virtually impossible to find? I know there are aftermarket power supplies that would work with a real U67.

I'll post pics of the mic insides when I get home this evening. My computer was intractable yesterday.

Bdub · « **Reply #20 on:** October 22, 2013, 02:00:01 PM »

Update:

I emailed Peluso labs, and Jim called me within 45 minutes of the email!

He's had some experience with Fred's work, and is sure he can modify a Peluso power supply to work with the mic.

As an aside, I mentioned the "handcrafted"

look of the power supply.
He said: "They all look like that. And I don't think he ever made two the same."

Thanks so much for the input, guys. And special thanks to Klaus for this wonderful resource.

If you're interested, I'll keep you posted on how it goes.

klaus · « **Reply #21 on:** October 22, 2013, 04:05:25 PM »

Yes, Please do.
Best of luck!

soapfoot · « **Reply #22 on:** October 22, 2013, 09:34:41 PM »

I'd love to see the inside of the mic, if you can snap a pic.

It's unclear if the original BV No 12 transformer has been replaced, or is present. To me, this would be the deal-maker or deal-breaker for whether or not this mic is a good candidate for restoration to original specs.

Kai · « **Reply #23 on:** October 23, 2013, 08:33:45 AM »

It seems the owner is very happy with the sound of the mic as it is.
So I wouldn't suggest to restore it to original as this would mean changing the sound.

Depending on the kind of mod it might anyway be almost impossible to restore it to 100% original again, as you won't be able to obtain the "original" parts.

I curious what this mod is, as I can't see a reason to modify an U67.
Even the tube (EF86) is still available for reasonable prices.
Maybe because someone prefers "triode"-sound.

If we had some very detailed pictures we could "reverse engineer" the mod, would be interesting, specially as Fred is no longer with us.

Regards
Kai

Bdub · « **Reply #24 on:** October 23, 2013, 11:05:46 AM »

I'll be boxing it up tonight, so I'll get some up close and personal pics of the mic itself.

Bdub · « **Reply #25 on:** October 23, 2013, 07:33:08 PM »

Here's the pics!

Mic Front:

Bdub · « **Reply #26 on:** October 23, 2013, 07:39:12 PM »

Mic Rear:

Bdub · « **Reply #27 on:** October 23, 2013, 07:40:38 PM »

Bottom:

Bdub · « **Reply #28 on:** October 23, 2013, 07:41:44 PM »

Inside front:

Bdub · « **Reply #29 on:** October 23, 2013, 07:42:53 PM »

Inside front close-up:

Bdub · « **Reply #30 on:** October 23, 2013, 07:43:59 PM »

Inside rear:

Bdub · « **Reply #31 on:** October 23, 2013, 07:45:01 PM »

Inside rear close-up:

Bdub · « **Reply #32 on:** October 23, 2013, 07:48:13 PM »

Inside bottom with S/N:

Bdub · « **Reply #33 on:** October 23, 2013, 07:49:34 PM »

Capsule front:

Bdub · « **Reply #34 on:** October 23, 2013, 07:55:55 PM »

Capsule front close-up:

Bdub · « **Reply #35 on:** October 23, 2013, 07:56:46 PM »

Capsule rear:

Bdub · « **Reply #36 on:** October 23, 2013, 07:57:42 PM »

Capsule rear close-up:

klaus · « **Reply #37 on:** October 23, 2013, 11:09:31 PM »

Not exactly lovingly assembled. Not worth restoring in my mind: from the connector to the transformer... gone...gone...gone...

The capsule could need some loving, too. (No, don't use anything mechanical to clean the diaphragms. It will destroy the sputtering!)

Jim Williams · « **Reply #38 on:** October 24, 2013, 11:53:50 AM »

Agreed.
However, there are some rather low end parts in there like that blue electrolytic cap, a blue mylar cap, a ceramic disc cap and it looks like either a Jensen or Reichenback transformer. Brown and red wires are Jensen's primary color scheme. Swapping those caps might make it sound a bit more open depending on your confidence in swapping components. The capsule is filthy.

soapfoot · « **Reply #39 on:** October 24, 2013, 02:47:57 PM »

transformer could be a newer Haufe... I've seen them in that type of case.

Agreed with all of the above. The critical bits that make it a "U67" are gone, save for the capsule (which itself isn't in the best of repair, though it could still sound just fine).

Bdub · « **Reply #40 on:** October 28, 2013, 10:54:38 AM »

It's an oddball, but it's been a useful tool for me.

It's now winging it's way to Peluso Labs for evaluation...

I'll let you know what John says.

Thanks again, everyone, for your interest.

klaus · « **Reply #41 on:** October 28, 2013, 01:18:44 PM »

Just remember to not let him touch the capsule with any mechanical means.

R/E/P Community

Author Topic: Fred Cameron U67 (Read 14082 times)