Neumann N61v capacitor upgrade

[monsieurpr]

Hello.
I have a Neumann N61v (preamp removed) power supply unit for M582 or CMV563 microphones.
I would like to change the electrolytic capacitors to protect the transformer and microphone in case they would fail in the future.
I have a few questions for which I couldn't find the answer in the existing threads on the forum.
Maybe someone will be able to give advice.

I intend to replace the old 22µF high voltage capacitors with new ones with the same capacitance as the polarization of the capsule draws very little current.

For the low voltage capacitors that filter the tube heating, I wonder whether it would be a good idea to increase the value of the 1000µF to give more current stability and make the voltage rise more slowly which may be better for the filament.
Modern capacitors are so compact that 15000µF would fit in the same volume!
However,
- Can it bring any noise improvement?
- And can it be detrimental? Indeed, increasing the value will increase the inrush current at start. Could it kill the diodes? The original GY101 diodes are rated 100mA, and so is the fuse.
I am not so concerned about the transformer because it looks oversized (in comparison with what you find in modern PSUs).

Other question (more for anode polarization capacitors): the old electrolytic capacitors have a metalic casing connected to ground (casing is the - pole).
Is it just for conveniency for the mechanical concept or does it bring any shielding against transformer electromagnetic leakages?
In the past I converted chinese PSUs to 5.8V and 120V voltages but never could totally get rid of the transformer hum even after using a better quality transformer from Toroidy.

So, should I shield new capacitors using aluminum foil ? 1000µF capacitor can be found with casing connected to - pole (EPCOS B41789) but I could find the equivalent for 22µF.

Thank you very much.

 

[monsieurpr]

A picture to illustrate.
I am still wondering which capacitor to use as a replacement.
Did anyone experienced larger values than the 1000 microF?
Thank you.

 

[rock soderstrom]

A picture to illustrate.

Hi, it's always better to post the relevant schematics as we don't know them by heart and have to search for them ourselves to answer your questions.


Basically, you should ask yourself a few questions about what you want to achieve and why. This is historical equipment, I think for you a practical use is in the foreground, therefore an exchange of individual components makes sense to be able to operate the power supply reliably.

What is the current condition? Are you satisfied with the actual performance? Are you bothered by humming or other noises?

Basically, the designers usually had something in mind when they planned these devices. On the other hand, you can pimp the PSU moderately, but I wouldn't overdo it.

Concretely, you can enlarge the HV and heater electrolyte caps a little, depending on the space available. I'd use 47uF for the 20uf capacitors and double the C4-C6. I wouldn't go higher than that, as it can stress the rectifier diodes, as you rightly pointed out. Under certain circumstances, you could also update the rectifier with something more modern, but I'm sure some people would consider that blasphemy. Basically, I would choose very high-quality components because they last longer.

I am not sure if the capacitor housing on GND has a shielding function. But I am sure that you can build quiet power supplies with conventional capacitors.

Good luck!

 

[monsieurpr]

Hello and thank you for your comments.
You are right, I should be more precise.
I am not a collector and I am mainly after performance (regarding noise level) and reliability.
I noticed a significant voltage ripple on the 5.8V filament heating voltage (which is not surprising as it is not regulated). That's why I wondered whether increasing the capacitors value would have an influence on the noise level.
However, I have to say this Neumann PSU is very nice as is. It has slightly less noise than my Tubelife 257 (which is very nice) although the N61 is not regulated for the 5.8V voltage. My chinese PSU (converted to 120V/5.8V) is even more noisy and still has a hum (even with upgraded transformer).

So I wonder if the N61 can be further optimized (without changing the whole design) and what makes it quieter than modern power supplies.

Comparing N61v design versus modern PSUs, I can see:
- 2 transformers on the N61v instead of 1 with 2 voltages on modern PSU
- Germanium rectifier diodes instead of silicium
- Tube voltage regulator instead of a zener diode
- Additional component on the N61v noted "Dr" which I suppose is an inductance (although I was unable to identify it in my PSU)


I will let you know about the capacitor change.

 

[rock soderstrom]

Additional component on the N61v noted "Dr" which I suppose is an inductance (although I was unable to identify it in my PSU)

Right, "Dr" stands for Drossel, german for choke.

I will let you know about the capacitor change.

 

[rock soderstrom]

2 transformers on the N61v instead of 1 with 2 voltages on modern PSU

One of those "transformers" is actually the choke!

Nice gutshots on radiomuseum.org

Netzanschlussgerät N61V Power-S Neumann & Co, Georg; | Radiomuseum

Edit:

If you are looking for threaded capacitors to approximate the original look.

https://www.die-wuestens.de/dindex.htm?/kond.htm
Search for screw mount caps on this site, unfortunately I can not link directly to it.

 

[jokeramik]

Comparing N61v design versus modern PSUs, I can see:
- 2 transformers on the N61v instead of 1 with 2 voltages on modern PSU
- Germanium rectifier diodes instead of silicium
- Tube voltage regulator instead of a zener diode
- Additional component on the N61v noted "Dr" which I suppose is an inductance (although I was unable to identify it in my PSU)

In the production time of this unit they have only germanium recitifiers. Why? Silicon rectifiers came into production later.
Why only one transformer? Why not? You have two windings on the transformer. That was an economic decision. At that time there were no transistors that could handle such high voltages. In addition, operational reliability is significantly higher. For this reason, mainly passive components were used in filtering. ST -> This is a special stabilizer tube.

The inductor have only two leads.

This is a very early power supply made by the former VEB Mikrofontechnik Gefell in the GDR. Now it is Microtech Gefell.

Other question (more for anode polarization capacitors): the old electrolytic capacitors have a metalic casing connected to ground (casing is the - pole).
Is it just for conveniency for the mechanical concept or does it bring any shielding against transformer electromagnetic leakages?

At that time, electrolytic capacitors with this capacity and these mechanical dimensions were produced in such a way that they could be fastened well. Modern production methods came much later.

Also preamps like the V 241 use the same capacitors with this mechanical dimensions.

Best regards!

 

[David König]

Folks, if it works, don´t fix it. You devalue the historical piece for ever. If you want a new PSU, buy a new PSU instead of totally rehashing the old one.
If it doesn´t work, find the element which is wrong and replace it with the most adequate modern element. I, as a collector, do it the way that I left the old element in place, just unconnected so that any other collector would know what element was there originally.