Neumann U48 power supply

[Handcrafted Tone]

Does anyone have info on the U48a, or a schematic of the power supply? A friend of mine has the "nuvistor" (a) version, but no power supply or cable. I'd like to build a PS, and maybe mod it back to the VF14.

also, where can I find the 6 pin touchel cable? Has anyone been able to fit a 7 pin xlr in there?

Thanks in advance. I'll post pics later.

 

[SSLtech]

Tuchel connectors: I'd ask Harald:

connector(at)gmx(put dot here)de -he has a lot of that sort of thing. -let me know if you're going to order from him: I need a pair of 12-pin line Tuchels, and shipping would probably be more reasonable if it's split...

To use the VF14, you'd need to have the original transformer... isn't it usually replaced as part of the VF14 "Upgrade"? Don't bother going VF14 unless you have the transformer: one without the other is a complete waste of money.

Keith

 

[jensenmann]

there are several guys at german ebay (.de) who sell the cables and connectors.

 

[SSLtech]

Yeah, Harals is one of them, I think his user ID is 'Connector115' or something similar...

Keith

 

[Martin B. Kantola]

[quote author="SSLtech"]
To use the VF14, you'd need to have the original transformer... isn't it usually replaced as part of the VF14 "Upgrade"? Don't bother going VF14 unless you have the transformer: one without the other is a complete waste of money.
[/quote]

Good news, for the Nuvistor "upgrade" the transformer is not replaced. Actually, that's probably part of the reason why it sounds so bad, serious mismatch I've been told.

Martin

 

[Handcrafted Tone]

Thanks for the replies...

I emailed Harold to see if he has the tuchel I need. Keith, I'll let you know when he replies. I had a hard time finding anything on the German ebay site..... mainly because I can't speak German...
:grin:

As for the VF14, this guy has cloned the origional:
http://www.saturn-sound.com/products/replacement valve.htm

Price - £ 275.00

I'm still looking for a power supply or nuvistor u48 schematics, so far the only schem I can find is for the VF14:http://vintageking.com/site/files/images/u48.gif

 

[gyraf]

It's not a clone, but a completely different tube put into the can. Probably sounds decent, but not to be confused with a real VF14!

Jakob E.

 

[skipwave]

You could check with Peluso. Page says email for price.

http://pelusomicrophonelab.com/vacuumtubes.html

 

[Gus]

did you check the meta?

The schematic in that link has most of what you need to know.

did you search Klaus's forum for posts from Oliver?

 

[Handcrafted Tone]

Thanks Gus, the U47n (nuvistor) schematic I found on adamasd's web site should be pretty close to the U48a (nuvisor). Looks like I just need 110V for the nuvistor, and 105V for the VF14. (on pin 5)

I don't think my friend wants to drop the money on a replacement tube yet, so I'm building the 110V PS for now. I just need those connectors.

Keith, I think the ebay guy your talking about is connector111. He hasn't emailed me back yet.

 

[Handcrafted Tone]

Damn, $200 for the U47 cable on evil bay after shipping from Amsterdamn....

Is it worth it? I only need the tuchel on the mic side, I think I'm going to hold out for a better deal.

 

[SSLtech]

[quote author="Handcrafted Tone"]Keith, I think the ebay guy your talking about is connector111. He hasn't emailed me back yet.[/quote]
That's him.

Good luck with it: -Which capsule is in this particular '48? KK47 or M7? -Just curious.

Keith

 

[olafmatt]

[quote author="Handcrafted Tone"]Is it worth it? I only need the tuchel on the mic side[/quote]

In case that's a normal 7-pin Grosstuchel you can get them from http://www.conrad.de. Item number is 738973 (for female cable plugs) and it costs 17,57 EUR incl. tax. AFAIK the 6 pin Tuchel plugs on some Neumann mics are basically compatible with 7 pin (which have an additional pin in the center), please correct me somebody in case that's wrong.
I'm not sure whether Conrad ships oversea, if not I could order the plugs for you.

Olaf

 

[olafmatt]

Sorry, I re-read the initial posting again, you're probably searching for a 6-pin Kleintuchel female cable plug... that's item number 738760 for 7,64 EUR.

Olaf

 

[Handcrafted Tone]

I promised pics... here they are

[quote author="SSLtech"]Which capsule is in this particular '48? KK47 or M7? -Just curious.

Keith[/quote]

I'm not sure, but it is looking dirty. How much do you think it would cost for a professional to clean it? Or is this something you could DIY?

 

[Handcrafted Tone]

So I got a hold of a real neumann U47a/U48a (nuvistor) power supply, but it's putting out 300VDC instead of 110VDC. I'm getting 300VAC on the secondary of the mains transformer... Why would they step up the voltage if the mic is only asking for 110VDC? Am I missing something? I'm also confused about this part below.

looking at the rest of the circuit, this has to be a bridge rectifier, but where is the voltage regulator?

here's a rough schematic

The caps are 33uf 350V, and the resistors are 1K


after the mystery part, I'm getting 390VDC.:shock: about 280 volts more than I need.

here are some pics inside the Neumann PS
http://handcraftedtone.com/Pics/U48PS/U48a-PS.jpg
http://handcraftedtone.com/Pics/U48PS/U48a-PS2.jpg


Any help is extremely appreciated

 

[jensenmann]

It´s a Selenium Bridge rectifier which is probably dead. Its made for max 250V/ 75mA. B+ output is the red wire

 

[Gus]

did you use a load on the supply?

basic old school power supply design.

needed for a circuit like the u47/48 with the parts used at the time.

Basic stuff, I guess you did not use ohms law did you google power supply design?

The B+ will drop under load, first GUESS
200V / .04A = 5,000 ohms series resistors in the supply(EDIT 13cw4 has a 60ma heater currrent)
now the supply will drop under load and the series resistors will need to be adjusted in value. your drawing shows 2.5k if the resistors are 1k like you posted

Make a load for about 105 VDC at rated current
then calculate the wattage
you don't want to power this supply up without a load

 

[Gus]

update?

 

[Handcrafted Tone]

Yeah I loaded the PS, the problem was with the Selenium Bridge rectifier. I replaced it with four 1N4007 diodes. I had to adjust the series resistance (I just took the parallel 1K out). Works great.