2X2A X-ray tube
Table of Contents


The 2X2A is a high-voltage rectifier tube, which when supplied with a sufficiently high voltage, is also an effective X-ray tube.

The cathode heater should not be powered, as doing so will cause the tube to draw excessive current which will cause the HV supply voltage to drop.
(Unless you have a supply capable of supplying 50KV at >100mA, in which case the anode will likely become white hot and melt)

I powered the tube with a 10-stage CW multiplier connected to a flyback transformer.
The exact voltage is unknown but it is likely to be around 50KV.
Any voltage above 10KV will produce detectable X-rays, but only a few will escape the glass, and in any case they will be very low energy and absorbed easily.

At 50KV, the X-ray emission was measured at >5RAD/H.
at 50KV, the measured radiation emission was 1000 times higher than at 25KV.

It is probably not advisable to increase the anode voltage much above 50KV unless you need to, as this will increase the risk of the tube failing-

"Failure modes for over-volting a HV valve include flashover surface discharge across outside of glass,
internal flashover, dielectric puncture of glass, glass electrolysis at seals,
and 'softening' of the vacuum by outgassing from the electrodes and glass wall.
- Proud Mary

I used 2mm lead shielding around the tube, the radiation level behind the shielding was less than 500uRAD/H, or about 2X the background count.
The following table shows the recommended thickness of lead shielding at various voltage ranges.

To remove the low energy X-rays (which can cause severe radiation burns), cover the gap in the lead shielding (through which the xrays are designed to pass) with aluminium foil.

Most of the X-ray emission in the 2X2A tube occurs around the base of the anode bell.

The following diagram shows how I constructed my shielded X-ray tube enclosure.


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