Luftwaffe NA8 utility power supply for 100 Watt Sender

[val]

The moving coil is powered though the spring. Overvoltage will zap that spring.

It can be repaired, depending where it exactly got broken...but it's very delicate job.

If you are very, very lucky, the spring is not broken, but it's connection soldering point

has melted and spring is just loose.

 

[kriegsfunker]

Thank you folks.   I have sent the instrument to a company here in California which repairs them.   Hopefully they can get me sorted.  In case they don't, I will work with Funksammler to get it fixed.

 

 

[kriegsfunker]

Turns out that the series resistor went bad.   That's why I wasn't getting any anode voltage reading.

 

 

[Funksammler]

Ah OK, I had assumed that the voltage instrument was pointing at 12V without any voltage being applied, but it seems that it was indicating 12V but not just HV, correct? In that case it is indeed just a matter of the series resistance (or the switch), which is a lot easier to fix....

regards,

Funksammler

[val]

17 hours ago, kriegsfunker said:

Turns out that the series resistor went bad.   That's why I wasn't getting any anode voltage reading.

So the instrument is OK and you haven't send it anywhere?

[kriegsfunker]

No, the instrument is cooked.   I have sent it to the repair business here in California.   If they can't fix it, I can send it to Germany for repair.

 

FS - The voltage instrument showed 12 V without pushing the blue button.   When you pushed the blue button for Anode voltage, there was no deflection in the meter, because the series resistor is dead.   I stupidly applied 100V to the meter without the series resistor and it snapped off the indicator with a bright electric spark.

[Funksammler]

Ah ok, I understand the story now. I definitely think a replacement with a similar movement is the way to go! Since they used standard internals for many of their instruments it should be possible to find something suitable...

regards,

Funksammler

[val]

20 hours ago, kriegsfunker said:

I stupidly applied 100V to the meter without the series resistor and it snapped off the indicator with a bright electric spark.

Happens even to the best of us! Once i connected a loudspeaker by the mistake to the mains...220v.

Naturally i wanted soldering iron to be heated up, but both had similar connectors

[kriegsfunker]

Thanks.  I feel a bit better.

[kriegsfunker]

Value of the voltmeter series resistor is unknown, because it was not functional.   There are some numbers written on it.  Is this indicative of its value?

 

 

[Funksammler]

It should be about 1000/12 times the 12V resistor. So if you measure the 12V resistor you should get an idea. You should also be able to measure some of the individual sectors of the resistor to check if the written numbers are indeed the resistance.

regards,

Funksammler

[kriegsfunker]

If someone has a spare 10cm diameter voltmeter that measures to 20 V with the marks in the picture, I will gladly buy it from you.

 

 

[kriegsfunker]

I haven't posted on my site for a long time.  Here's the new page on the NA8.  Most of the info is in this thread, but I wanted to dump onto my site:

https://kriegsfunker.com/restoration/NA_8_restoration.html

 

[kriegsfunker]

The voltmeter which I so stupidly damaged has been repaired by a friend of mine.  He also provided the correct series resistor for the Anode voltage measurement.

 

[kriegsfunker]

Do not turn on the low voltage portion of the NA8 without load.   No damage, but will peg the meter.

[kriegsfunker]

NA8 is fully operational from standard US utility power of 120 V.  

 

 

[kriegsfunker]

Now to start restoring the 100W.S.