I have a late 1950's Neuman U47 mic that has gotten noisy. Obviously, this mic deserves the best components available.
I don't have a scope, so can't test most thing, but I figure it might be a good idea to change the 64 year old electrolytics in the power supply.
Sure, they might still be fine, and they don't meke 'em like they used to, etc, but it seems logical to do it now.
There are two 1000uf / 50v, and those are no problem. I can easily fit Nichicon LKG's there.
However, there are also four 47uf / 250v axials, and I'm having a very hard time finding a suitable replacement even in a radial cap, hence this post.
The original caps are FRAKO GPF series, (polarized electrolytics) and are no longer made. I saw some vintage nos ones for sale, but what sense does it make to buy really old electrolytics?
I would love to pop some polystyrene's in there, but space is a real problem.
(I'm also not clear on whether I can use non-polarized caps there.)
Even a really good electrolytic, like maybe a Mundorf MLytic, is too big. The max diameter I can easily fit is about 20mm.
One alternative would be to use decent electros (or smaller film caps and glue them to a different area in the enclosure. However, that would require pretty long leads, maybe 4-6". Would that be a problem?
Or maybe use a bit less capacity? I assume these are bypass caps, yes?
Still Neuman surely knew what they were doing, so....
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I may just change the big caps first, and see how it sounds, but even if that cleaned things up, should I consider changing the others as well?
-----------------
Anyway, does anyone know of a really good, but fairly compact, cap I can use? (axial or radial, I don't care.)
- thx
I don't have a scope, so can't test most thing, but I figure it might be a good idea to change the 64 year old electrolytics in the power supply.
Sure, they might still be fine, and they don't meke 'em like they used to, etc, but it seems logical to do it now.
There are two 1000uf / 50v, and those are no problem. I can easily fit Nichicon LKG's there.
However, there are also four 47uf / 250v axials, and I'm having a very hard time finding a suitable replacement even in a radial cap, hence this post.
The original caps are FRAKO GPF series, (polarized electrolytics) and are no longer made. I saw some vintage nos ones for sale, but what sense does it make to buy really old electrolytics?
I would love to pop some polystyrene's in there, but space is a real problem.
(I'm also not clear on whether I can use non-polarized caps there.)
Even a really good electrolytic, like maybe a Mundorf MLytic, is too big. The max diameter I can easily fit is about 20mm.
One alternative would be to use decent electros (or smaller film caps and glue them to a different area in the enclosure. However, that would require pretty long leads, maybe 4-6". Would that be a problem?
Or maybe use a bit less capacity? I assume these are bypass caps, yes?
Still Neuman surely knew what they were doing, so....
------------------
I may just change the big caps first, and see how it sounds, but even if that cleaned things up, should I consider changing the others as well?
-----------------
Anyway, does anyone know of a really good, but fairly compact, cap I can use? (axial or radial, I don't care.)
- thx
"Noisy" may not be power supply caps.
Sell it to a good home. Someone with proper equipment and skills.
Sell it to a good home. Someone with proper equipment and skills.
Agreed. Please don't butcher this great, rare mic. Please leave it alone, for an expert only.
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I didn't realize this is the DON'T DIY forum.
My bad.
sheesh.
BTW, it's not a collector's item. It's a professional tool which gets used every day.
I guess I'll try a different forum......
My bad.
sheesh.
BTW, it's not a collector's item. It's a professional tool which gets used every day.
I guess I'll try a different forum......
Yes, this is the Do Not Everything Yourself Forum.
It is used every day - but it is not good enough for daily use ?
The "collectors" value of this mic is well over 10.000 $.
You are seemingly not aware that you will reduce it considerably
when you do what you intend and clueless as it seems in your
own words. No workshop equipment, no tools, no idea.
Sorry, but you described it this way.
And, as "always", pictures are missing.
It is used every day - but it is not good enough for daily use ?
The "collectors" value of this mic is well over 10.000 $.
You are seemingly not aware that you will reduce it considerably
when you do what you intend and clueless as it seems in your
own words. No workshop equipment, no tools, no idea.
Sorry, but you described it this way.
And, as "always", pictures are missing.
Hi,
They are right that modifying it can reduce its collector's value.
On the other hand, why keep a non-functional (with noisy sound) U47 microphone?
The noise may not necessarily come from the capacitors.
The issue could be with components within the microphone. The noise might be caused by the capsule, which can dry out and change its values over time. An ideal test would be to disconnect the microphone head and only connect a part of the microphone with the tube and transformer. If the noise persists, it's likely the capsule's fault.
Then, the VF14 tube might be faulty. If you have a tube tester, you can check its values. But be careful, it's a rare commodity. It may not hold a vacuum anymore and operate outside its values.
Of course, some other components could be faulty, but typically, resistors, mica capacitors, and transformers endure.
Caution! The power supply should never be turned on without the microphone connected with a cable. The power supply generates a direct current voltage of 105V / 40 mA, but only when connected to the microphone. It was a replacement for direct network connection (in Germany after the war, there was 110V DC in the grid). If the capacitors are damaged, I would replace them with 47uF / 400V capacitors because when the power supply is not connected to the microphone, the voltage in the power supply can rise significantly.
The same company Neumann has in the schematics once indicated 5 x 32 uF, and another time 5 x 40 uF / 350 V. The aim is to provide clean power to the microphone, as the 105 V / 40 mA power supply is used for both the tube and its cathode (with a fixed bias of 1.1 V) and for the anode section with the transformer.