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 21 
 on: March 16, 2017, 12:56:10 pm 
Started by MikeCheck - Last post by Jim Williams
The 317 regulator design is the better choice of these. I would probably pop for an LT1086 instead.

If you use the zener clamp solution, place a small film cap across it like .01 uf. Zener's generate a lot of noise and that will shunt that noise off to ground.

 22 
 on: March 16, 2017, 12:53:23 am 
Started by MikeCheck - Last post by uwe ret
All the schematics for this family of power supplies I have do show the mains transformer to be capable to be configured for operation with either 110 to 120Vac/60Hz or 220 to 240Vac/50Hz.
Your photo of the mains transformer clearly shows the corresponding dual primary arrangement with its current implementation for 220-240V.

 23 
 on: March 15, 2017, 11:54:38 pm 
Started by MikeCheck - Last post by MikeCheck
Awesome info Uwe! Thank you very much.

I think I'll build and install your circuit. I'll update when done.

I've attached more pictures of the PSU for every ones enjoyment. The pics are a little dark. Sorry. Note that the serial number is "011"

Also, no markings on the power transformer. Anyone know if this can be changed to 110VAC ??

 24 
 on: March 15, 2017, 10:58:16 pm 
Started by MikeCheck - Last post by klaus
Thanks, Uwe.
I suggest that anyone who owns or repairs N52 or NN48 supplies copies these schematics, for future reference!

 25 
 on: March 15, 2017, 06:33:33 pm 
Started by MikeCheck - Last post by uwe ret
Stabily Replacement

 26 
 on: March 15, 2017, 06:32:52 pm 
Started by MikeCheck - Last post by uwe ret
SK33d instructions

 27 
 on: March 15, 2017, 06:31:50 pm 
Started by MikeCheck - Last post by uwe ret
SK33d

 28 
 on: March 15, 2017, 06:31:11 pm 
Started by MikeCheck - Last post by uwe ret
NN48b

 29 
 on: March 15, 2017, 06:30:26 pm 
Started by MikeCheck - Last post by uwe ret
Looks like someone performed a previous 'repair' and replaced the original Stabilyt cells.
Stabilyt cells have a typical life expectancy of 2 to 3 years and been discontinued for nearly 50 years. These replacements (1,5/300 = 1.5V/300mA) are certain to be dead by now also.

At the time, Neumann made available for a brief transition period a solid-state replacement board SK33d, before redesigned successor supplies were introduced, among them NN48b. With modern voltage regulator devices more effective solutions are possible.

For the rehabilitation of vintage power supplies for use with the precious AC701(k) tube I have developed another 'Stabilyt Replacement' circuit with gently ramping supply which reduces stress on a cold tube filament. While working on these power supplies it does make sense to examine the high voltage plate/bias voltage stabilization and consider replacing the gas discharge tube (150B2) with a suitable 150V/1W Zener diode.

File size restrictions will result in multiple postings for the attachments.

 30 
 on: March 15, 2017, 05:36:49 pm 
Started by MikeCheck - Last post by MikeCheck
EDIT:
Just realized that the third component is not a diode on the schematic, it is in fact the third cap. Duh!
and...... it seems to read either 1.5 or 7.5/300.

Any thoughts?

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