Proud Mary wrote ...

I think the Russian translation is a bit dodgy here: this part is what was called a 'booster diode' in UK thermionic valve TV terminology. It is not a 'kenotron' - an old term for a HV thermionic diode rectifier as used in, for example, the power supply of X-ray sets.

The "Anode voltage: 100V" means the voltage relative to the cathode, the voltage drop across the device when the valve is conducting.

On the half-cycle when the diode is not conducting, it can withstand 25 kV.

I can't comment on the suitability of 3C18P as an X-ray source, though clearly field emission will occur if the valve is operated at 25 kV with a failed or disconnected heater supply.

While the pictures don't show any special internal shielding, as one does see on some Soviet-era colour TV HT stabiliser triodes, it is always possible that the valve envelope may be made of lead glass to attenuate unwanted X-rays.

alf wrote ...

The "Anode voltage: 100V" means the voltage relative to the cathode, the voltage drop across the device when the valve is conducting.

Wow, that seems very low. How come vacuum tubes arent often used in CW multipliers?

On the half-cycle when the diode is not conducting, it can withstand 25 kV.

When you say it can "withstand" 25KV, do you mean that the maximum voltage at which a spark wont jump between pins and anode cap is 25KV?

I can't comment on the suitability of 3C18P as an X-ray source, though clearly field emission will occur if the valve is operated at 25 kV with a failed or disconnected heater supply.

Well I was thinking of >50KV :D

While the pictures don't show any special internal shielding, as one does see on some Soviet-era colour TV HT stabiliser triodes, it is always possible that the valve envelope may be made of lead glass to attenuate unwanted X-rays.

Ahh. Well I assume that at 50KV, xrays would pass through lead glass, atleast I hope so. Worth a try anyway

Conundrum wrote ...

I'm adding my data point here.
Tried this with a few 5642's (cheap) and DAC32 (old AM radio valve from 12V radio)
At around -7KV enough EUV gets through the fluoroscope screen to activate the phosphors, haven't dared run it any higher for safety reasons.
At this point the tubes were glowing bright blue or green, this apparently shows possible X-ray potential..


EDIT: This was a spectacularly bad idea, the DAC32 didn't survive long. On the flip side I now know to immerse them in oil to stop the tubes eating themselves, and put the whole thing in a lead box with a pyrographite or thin foil window to block the EUV and low energy high BOE X-rays that cause most of the damage.
BTW watch out, said low energy X-rays do not show up on most Geiger counters. A good way to detect them is to use a piece of GdO2 based scintillator screen with its phosphorescent side facing a silicon photodiode or Proud Mary's idea of a CdS photoresistor and a pyrographite "end window".
This seems to work pretty well as long as the rest of the sensor is sealed up to stop light getting in.

An alternate method is to take a piece of failed EL sheet and gut it, taking out the light emitting layer and sticking it to a piece of pyrographite with a silicon diode underneath connected to a transimpedance amplifier.
This also means you can make accurate measurements of dose at a range of energies by adding a second filter inline to block everything below the half value thickness.

-A
#include "Shielding_dosimeter_etc.h"