Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Kai]

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]

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]

Agreed with both of the above.

[klaus]

(...) 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]

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]

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]

Yes, Please do.
Best of luck!

[soapfoot]

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]

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]

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

[Bdub]

Here's the pics!

Mic Front:

[Bdub]

Mic Rear:

[Bdub]

Bottom:

[Bdub]

Inside front:

[Bdub]

Inside front close-up: