Luftwaffe NA8 utility power supply for 100 Watt Sender

[kriegsfunker]

After a year of waiting, I got this power supply.  It weighs around 90 KG and broke my hydraulic hand-truck moving it to the shelf.   It looks complete inside, so I will restore it  (slowly).

 

 

 

[kriegsfunker]

Closeup of the data plate

[val]

Thank you Yuri, very nice! I'd love to see the inside of it.

Here is for comparison another NA8, front panel seems little bit different,

quite possibly doctored...

https://picclick.de/Gehäuse-Sender-Netzteil-NA8-der-Wehrmacht-ideal-für-Selbstbau-Röhrenverstärker-263844641328.html

 

[kriegsfunker]

Yeah, definitely doctored, and stripped.   Here's my interior.  It's definitely restorable, which I've started doing now.

 

 

[kriegsfunker]

Most of the weight is in the transformers.   Behind the selenium rectifier array, there's a double winding massive transformer which probably weights 1/2 of the device.  There are 4 other transformers in there as well.

[Funksammler]

Nice one! I like that you can adjust the output power of the transmitter by setting the anode voltage. The vehicle power supply does not have this facility, it just generates 1000V. The NA6 was often used with the 100 W.S. and a Morseschreiber as a Luftwaffe beacon station. The luftwaffe multi engined aircraft could use their PeilG6 radio direction finders to navigate using these beacons.

[kriegsfunker]

Thanks FS.  The AC input voltage can be changed by connecting to the appropriate terminal on the input transformer.

This will also allow me to finally build a tube tester for the RS-237.

[kriegsfunker]

A few years ago, I was offered one of these.   The insides are a bit different.  Notably, the selenium rectifiers are different.

Edited January 2, 2019 by kriegsfunker

[val]

Yuri - one special request please - when you start restoring it, show what type of Glimmlampe there is.

[Desert Rat]

Hello to all you technical experts,

I just wondered where on earth do you find these superb radio sets etc....I would have thought most would have been destroyed after WW2 but it seem there are many more to be found...Good Luck!

Thanks for showing us on MCN these rare and great memorable items.

Desert Rat

[kriegsfunker]

2 hours ago, val said:

Yuri - one special request please - when you start restoring it, show what type of Glimmlampe there is.

Of course!

[kriegsfunker]

6 hours ago, val said:

Yuri - one special request please - when you start restoring it, show what type of Glimmlampe there is.

Do you have one of these?

[kriegsfunker]

Here's a photo from a field manual showing the NA8 installed in some vehicle. Note the different locations of the power terminals:

 

 

[val]

On 03/01/2019 at 04:17, kriegsfunker said:

Do you have one of these?

No, my friend has one.

[kriegsfunker]

Restoring the main transformer.   

 

 

[kriegsfunker]

Testing the high voltage rectifier.  It works.

[kriegsfunker]

18 hours ago, val said:

No, my friend has one.

Here is the lamp

 

 

[kriegsfunker]

Val - please ask your friend to measure the resistor on top of the huge capacitor under the transmitter power output terminals.  My resistor is dead.

 

[val]

8 hours ago, kriegsfunker said:

Here is the lamp

Thanks! Any visible markings there?

[val]

On 05/01/2019 at 08:03, kriegsfunker said:

Val - please ask your friend to measure the resistor on top of the huge capacitor under the transmitter power output terminals.  My resistor is dead.

Asked - sorry, his set missed that resistor alltogether

[kriegsfunker]

What resistor value would you use for a "bleed-off" resistor on a 32 uF 1.2 kV capacitor made for 1000 Volts DC at 250 mA?

Edited January 7, 2019 by kriegsfunker
Correction

[val]

59 minutes ago, kriegsfunker said:

What resistor value would you use for a "bleed-off" resistor on a 32 uF 1.2 kW capacitor made for 1000 Volts DC at 250 mA?

If i have to guess i'd use something around 10MΩ as a permanent bleeder.

This would give a slow discharge something between 5...10 min.

[kriegsfunker]

Here is a great site for calculating discharge (bleed) resistor values:

https://www.engineersedge.com/instrumentation/capacitance_discharge/capacitance_discharge_calculator_12909.htm

[kriegsfunker]

Based on the following calculations, I'm buying this resistor:

 

[Funksammler]

You probably want to give the resistor clamps a good clean, I find it hard to believe that the resistor wire (embedded in glaze) is defective. It looks like the clamps just connect to the wire by pressure...

regards,

Funksammler