Netzanschlußgerät 8 (NA8)

 
This is the Luftwaffe version of the utility mains power supply for the 100 Watt Sender (Transmitter).  The primary purpose of the 100W.S. was mobile operation, specifically in vehicles such as the Kfz. 17, and Kfz. 61, and the power supplies originally designed for it reflected this requirement.  Originally, the 100W.S. was powered from a 12 volt vehicular battery and a U100 Umformer.   For prolonged stationary operation, a gasoline-powered generator (HNG-100) was used.  Both the Heer and Luftwaffe had requirements for stationary operation, where the 100W.S. needed to operate using local utility power. 

So the NA8 was produced for the Lufwaffe, and the SGLT-100 was produced for the Heer.  These power supplies operated from utility power and supplied the filament voltage of 12-15 volts and anode voltage from 800-1000 volts to the 100W.S. and delivered the required current.

Restoration page for the NA8

 
Front panel of the NA8.   The switch on the lower left turns on filament power of 12-15V  to the 100W.S.   The actual filament voltage to the tubes is controlled by the "Heizung" knob on the 100W.S., and should be exactly 10.5 V.  The rotator switch on the right controls the anode voltage.   The anode function of the voltmeter on the 100W.S. should ideally show around 800 V when the anode power is being delivered, and should show 200V more when the CW key is pressed.   200V gets taken off as -200V of bias voltage, and pressing the key will release that 200V making anode voltage around 1000V on the 100W.S. voltmeter.   The Anodenspannung settings allow the operator to compensate for different power levels from the grid.



 Top of the NA8.   There are 8 screws that are removed to access the electronics of the NA8.   The NA8 becomes very hot during operation.



 
 Every side of the NA8 has removable panels for easy access to the different sections of the power supply for work and servicing.  Removing them also makes this very heavy device a little bit lighter.



 
 This is where the connectors get plugged in.   Utility power on the left.  Ground in the middle, and the 100W.S. on the right.



 
S.A.F. is for Süddeutsche Apparate-Fabrik, Nürnberg.   This unit was manufactured around March 1944.  The "Ln" designator represents a contract for the Luftwaffe.


 

The special voltmeter which measures the output voltages of the NA8.   It is critical to measure the anode voltage through a loading resistor, or else the meter will be destroyed.


 
 
After restoration, with the cover removed.  Most of the main components were functional.   Electrolytic capacitors were all replaced.   Selenium rectifiers were replaced with modern silicon ones, and a voltage compensating resistor was placed in series with the high-voltage rectifier to dampen the voltage spike when capacitors started to charge, since the silicon rectifiers are a lot more efficient than the old selenium ones.



 
 Here the electrolytic capacitors have been restored.  The electrolytics are encased on Bakelite, which is the first time I've encountered this.  The high-voltage selenium rectifier has been replaced with a silicon diode bridge with an upper limit of 3000 volts, but even that level is not sufficient to protect against the initial voltage spike of the charging capacitors.   A series resistor of 46 Ohms was placed after the rectifier to limit the initial voltage spike.




The low voltage capacitors have been similarly restored.  The light-grey cover hides the loading resistor for the voltmeter.



 
 This is the high-voltage step-up transformer.   Input voltage has been set at 125V (American outlets).




Below is the low voltage transformer, which has also been set to 125 volts.   Above it are two of the filter chokes.




The high-voltage transformer from behind the unit.  It has been tested to 3,600 volts.

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