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Author Topic: Neumann N52a: Voltages and Variants  (Read 1597 times)

fffaustino

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Neumann N52a: Voltages and Variants
« on: January 28, 2020, 01:32:06 pm »

Hi Klaus,

I have recently recapped a Neumann n52a and now i am trying to calibrate it for one km54a.

I have checked voltages on the mic side and, after some calibration with the internal trim pot, the heater value seems to be correct (3,93V), but B+ seems to be a bit low (117,3V).

Does it matter? Should i try to get a higher B+ value? In that case, how should i proceed?

Any advice really appreciated..thanks

Alfredo



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klaus

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Re: Neumann n52a voltages
« Reply #1 on: January 28, 2020, 02:46:29 pm »

The easiest way to adjust the B+ is to reduce R2, the first of three dropping resistors. It is the resistor right after the tube.
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Klaus Heyne
German Masterworks®
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fffaustino

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Re: Neumann n52a voltages
« Reply #2 on: January 28, 2020, 02:55:23 pm »

Thanks so much for your quick response, Klaus,

I will try to calibrate B+ that way.

Many thanks and best regards from Spain!

Alfredo
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klaus

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Re: Neumann n52a voltages
« Reply #3 on: January 28, 2020, 03:02:59 pm »

Please keep in mid: the B+ voltage in N52 is not regulated, i.e. variations in AC line voltage out of your wall plug will also vary B+.
So, before you permanently adjust B+, make sure to measure your AC voltage in the building where you intend to use the N52, to determine a mean level.
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Klaus Heyne
German Masterworks®
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fffaustino

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Re: Neumann n52a voltages
« Reply #4 on: January 28, 2020, 03:29:59 pm »

great, i will do.

Thanks again!
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uwe ret

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Re: Neumann n52a voltages
« Reply #5 on: January 29, 2020, 07:21:13 pm »

Actually, there is regulation of the B+ voltage via the gas discharge tube model 150B2. For more information see:
https://www.radiomuseum.org/tubes/tube_150b2.html. After it has fired (at around 180V) the voltage drops via R1 (1 kΩ) and the internal rectifier resistance to 150 ± 5V. If this tube is defective, it can be replaced with a 150V/1W Zener diode. However, since you measured 117.3 V (under load of the microphone?) I definitely would not bother, as this is darn close enough to the nominal 120V. I assure you, that you could neither hear nor measure any difference in the connected microphone's performance.
There are useful links explaining the voltage regulation function and detailed specifications at : http://www.r-type.org/exhib/aai0253.htm
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klaus

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Re: Neumann n52a voltages
« Reply #6 on: January 30, 2020, 02:17:02 am »

Hello Uwe,

1. Thanks for the links, but the 'Radio Museum' site requires log in and, worse, sign up requirements not fit for mere mortals (the proverbial stubbornness of the gate keeper at that site is a total turn-off). If you have a way to get into the info on that site, let us know!

2. I have not found that the 150B 2 tube in N52 stops DC voltage fluctuations due to AC line voltage variations. If my AC drops 3 Volts, the B+ drops commensurately (yes, the tube is working to spec). What am I missing?

3. I had sent you an email asking you for an N52 sub-part schematic (SK73 replacement brick). Did you get it?

Best,
KH
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Klaus Heyne
German Masterworks®
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afterlifestudios

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Re: Neumann n52a voltages
« Reply #7 on: January 30, 2020, 11:59:35 am »

The Radio Museum link from Uwe is a spec sheet with photos.  Here are the specs:

Country:Europe   
Brand:   Common type Europe tube/semicond.
Tube type:    Voltage Regulator, single   Power-supply
Identical to   150B2 = 6354 = SR57
Similar Tubes   
Other class quality (otherwise equal):
  CV2225 ; M8163
Base   Miniatur-7-Pin-Base B7G, USA 1940
Striking voltage: 180V min
Stabilized voltage 146 to 154V
Current: 5mA
Dimensions (WHD)
incl. pins / tip   x 54 x 19 mm / x 2.13 x 0.75 inch
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klaus

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Re: Neumann n52a voltages
« Reply #8 on: January 30, 2020, 02:27:27 pm »

Thanks. I can see that. But the page is a teaser page, and the relevant info on the tube and what other "club" members have to say is only accessible  for members.
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Klaus Heyne
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afterlifestudios

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Re: Neumann n52a voltages
« Reply #9 on: January 30, 2020, 05:30:52 pm »

Ah yes, I see.  It does seem like a rather arduous sign up process.  Looks like the members section has access to people selling etc.   But potentially more info as well. 
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uwe ret

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Re: Neumann n52a voltages
« Reply #10 on: January 31, 2020, 02:55:20 pm »

Try clicking on the link in the header box. Here is another way to access (perhaps):
http://www.r-type.org/addtext/add176.htm
and for the data sheet possibly:
http://www.r-type.org/pdfs/150b2.pdf
Let me know is this works.
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klaus

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Re: Neumann n52a voltages
« Reply #11 on: January 31, 2020, 07:19:45 pm »

Thanks, Uwe,
But I was referring to the "RadioMuseum" website, which is off-limits unless apply to become a member, succumb to an FBI background check, a body cavity search, and pay $25.- up front.

On a related note:
I tried several times to reach you via email but have not received a response; can you please forward me a schematic of the Neumann retrofit solid state kit for the N52a? (It goes into the slot where the SK73a Stabilit cell brick was located.)

Best,
KH
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Klaus Heyne
German Masterworks®
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uwe ret

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Re: Neumann n52a voltages
« Reply #12 on: February 01, 2020, 10:01:02 pm »

I do not have any information about a retrofit kit for N52a. There is a schematic for a N52t (solid state version N52) and the short lived SK 33d Stabilyt replacement kit. If all that is needed is to replace the Stabilyt section, I recommend the circuit I developed with an integrated regulator LM317.
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klaus

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Re: Neumann n52a voltages
« Reply #13 on: February 02, 2020, 01:06:55 am »

Here are two pix of the SK73t replacement brick that fits where the SK73 Stabilyt/NiCad brick used to be in N52a. This solid state heater voltage stabilizer and filter unit was retrofitted starting in the 1960s by Neumann to all N52 with leaky Stabilyt cells.

The hook up was simple and straight forward. No modification of the power supply was needed, and heater voltage was trimmed out with a trim pot mounted in the center, flanked by the two power transistors.

I have so far not been able to find a schematic for this unit.
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Klaus Heyne
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panman

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Re: Neumann N52a: Voltages and Variants
« Reply #14 on: February 02, 2020, 10:22:30 am »

Yes, I would like to have the schematics for that unit too. It is not much differend from the schematics of N52t, but it is differend enough. I have been too lazy to trace it all the way.
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Esa Tervala

klaus

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Re: Neumann N52a: Voltages and Variants
« Reply #15 on: February 02, 2020, 01:29:17 pm »

The SK73t and N52t heater voltage section have not much in common in components and circuitry. Anything with a circuit board that has an imprint like "SK73t" should have a circuit diagram somewhere...
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Klaus Heyne
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fffaustino

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Re: Neumann N52a: Voltages and Variants
« Reply #16 on: February 03, 2020, 10:16:42 am »

Hi again,

thanks so much Uwe and Klaus, for all the info, i really appreciated it. Sorry to say that I had not read it until this morning, after working on my psu...this is what i did;

I checked all the components carefully and discover that R3 and R4 were 10k instead of the 5k of the original schematic. I swapped them for two 8.2 kohms resistors and now i have gotten 119,5 at B+.
I really don´t know if i have acted correctly but the fact is that B+ is nearer from its ideal value now.

Many thanks again and let me know if i should correct something..

Alfredo
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uwe ret

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Re: Neumann N52a: Voltages and Variants
« Reply #17 on: February 10, 2020, 10:08:14 pm »

Pulling a few strings led me to this schematic for the N52t and SK72t. I am stll trying to ferret the one for SK73a.
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klaus

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Re: Neumann N52a: Voltages and Variants
« Reply #18 on: February 10, 2020, 10:26:07 pm »

Uwe, you are the best, and continue to be a treasure to the recording community.
Keep them coming! 
KH
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Klaus Heyne
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uwe ret

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Re: Neumann N52a: Voltages and Variants
« Reply #19 on: February 11, 2020, 11:34:19 pm »

BTW, SK73a is the designation of the Stabilyt module in the N52a as indicated in the previously posted schematic diagram.
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klaus

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Re: Neumann N52a: Voltages and Variants
« Reply #20 on: February 12, 2020, 02:37:03 pm »

SK73 suffixes are correct: 'a' = Stabylit, 't' = transistor (solid state) replacement module
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Klaus Heyne
German Masterworks®
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