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Author Topic: Neumann NSM power supply - looking for some advice  (Read 282 times)

Silvas

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Neumann NSM power supply - looking for some advice
« on: June 30, 2019, 09:03:44 pm »

Hello guys,

I came across this PSU which i'm bringing back to life.

 I've built the attached circuit to replace the original stabylit cells but i'm curious about heater voltage / current draw with this circuit. I'm loading the replacement circuit with a 39R resistor to simulate the heater load and i'm getting some voltage drop which I don't know is to be expected. I don't really know much about this PSU so I don't know what voltages I should expect to see on the heater supply under load (it's perfectly regulated at 4.00 volts unloaded but 3.20 volts loaded with the 39R resistor).

I'm curious too about voltage drop if any with the original Stabylit cells in place. Also...it ramps up pretty quickly, not sure exactly what to expect here or if a slower ramp-up is helpful here.

Also...the schematic I've found isn't that readable on some parts..Anyone has a decent one ?

Thanks guys !

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klaus

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Re: Neumann NSM power supply - looking for some advice
« Reply #1 on: June 30, 2019, 11:27:59 pm »

Uwe Sattler, Neumann's éminence grise, posted the Stabylit replacement circuit the company recommends. Use the search function and find it.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

Silvas

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Re: Neumann NSM power supply - looking for some advice
« Reply #2 on: July 01, 2019, 08:51:48 pm »

Uwe Sattler, Neumann's éminence grise, posted the Stabylit replacement circuit the company recommends. Use the search function and find it.

Klaus,

You mean this one ? I've already had it, not sure where i picked it up tho. Wasn't able to find anything under "Stabylit" search.  However, most of my answer's are still unresolved :-( Just want to fully understand the beast before moving forward. Thanks for your reply !

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klaus

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Re: Neumann NSM power supply - looking for some advice
« Reply #3 on: July 02, 2019, 09:32:28 am »

SK33 was the official Neumann retrofit drop-in transistor circuit or N52. It predates Uwe's circuit, which was described here a few years ago, and with drawing provided.I will try to find the link and post it here.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

uwe ret

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Re: Neumann NSM power supply - looking for some advice
« Reply #4 on: July 03, 2019, 12:46:12 pm »

The filament current of the AC701(k) is 100 mA. The 'Stabilyt replacement circuit' adds negligible current load to the supply. Thus there will be less than a 5V drop across the 47 Ω current limiting resistor at its input. A healthy NSM should provide at least 12 to 16 V at this point, and with the 39 Ω load still read above 7 V. By comparison, the original Stabilyt cells loaded the supply with around 100 mA of additional current.
If your supply (measured at the filament rectifier) collapses under the 39 Ω load, the selenium rectifier is suspect and probably has excessive internal resistance, requiring replacement. Typical replacement will be with a silicon diode bridge rectifier. Since they inherently have a much lower internal resistance, the 47 Ω resistor has been added to protect the transformer against in-rush-current surge and short circuits.
BTW. clicking on the schematic thumbnail the image opens up nicely with perfect clarity...
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Silvas

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Re: Neumann NSM power supply - looking for some advice
« Reply #5 on: July 05, 2019, 10:52:53 am »

Thank you guys, will re-check everything including the rectifier under load ! This is very useful info. Appreciate it a lot !
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Silvas

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Re: Neumann NSM power supply - looking for some advice
« Reply #6 on: July 05, 2019, 10:54:55 am »

Also...There's silicon diode bridges out there that resemble the original in terms of "looks" and terminal positioning ? Don't want to hurt the looks of it ;-)
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