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> Mystery Filament Voltage
Jimthecopierwrench
Posted: July 06, 2018 10:28 pm
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A while ago I finally scored a personal holy grail and managed to get my hands on 3 x-ray tubes.

However they have no numbers or even mfgr data. I know the plates run at 70KV - but not a clue what to feed the filament.

Not even sure what "colour" it should burn at between 12AU7 orange and HV rectifier white.

What would you guys do? Just variac it and take a guess?

Now as for the x ray bit.

I know these are dangerous as heck. When I get around to messing with them I'll be careful and work remotely.

All of their supplies appear to be toasted. I'll have to spin something up.

Thinking HEI ignition coil - I can get 60KV out of one without burning it up.

I assume I'll have emissions well below this though.









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Sch3mat1c
Posted: July 07, 2018 07:53 pm
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Turn it up until you get the emission you need. Probably low volts, under 6V I would think.

Should be tungsten (maybe thoriated), can't get away with an oxide cathode at these voltages.

Ignition coils, without rectification, of course won't make a very clean output -- pulsed, and the spectrum is all over the place. But hey, if you aren't doing XRD, that's fine. biggrin.gif

Tim


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Jimthecopierwrench
Posted: July 08, 2018 12:27 pm
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Quite surprisingly, the original supply was 60Hz AC! Of course the tube is "just" a big honking rectifier.

Schematic of supply (internal to head)

http://i815.photobucket.com/albums/zz79/Ji...zps1eetnvw4.jpg

X's denote open windings.

The .5 ohm windings were later discovered to be wide copper strips that ran from the front to the back of the trafo under the last layer of paper - don't know if they have properties as part of the transformer, or were simply used as mechanical parts to support the filament connectors and bring them to the side of the transformer facing the tube.

Transformer parts:

http://i815.photobucket.com/albums/zz79/Ji...zpswq6yoxlm.jpg

I had speculated that the long square covered winding might have been for feedback, but being two layers of 14AWG - and open at that - Input seems more likely.

The cores are lots of layers of very fine soft iron.

The whole shebang in a gallon of mineral oil, the tube suspended in an enclosure (graphite or a cousin?) with an aperture for business rays.

All of the secondaries seem intact. I've saved the cores and secondariies thinking they might have some future experimental value.

...

As for emission.

Presumably old scope CRTs should glow nicely to tell me I'm there. The trick I guess is are there potentially hazardous emissions at thresholds below visible fluorescence.












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