The DY86 (DY87, DY802) vacuum rectifier was used in most European black and white tube television sets. In hot-cathode mode, it was capable of rectifying up to 18 kilovolts at 0.5 mA. In cold-cathode mode, however, it withstands 40 kilovolts DC inverse for a short time, while providing some soft X-ray radiation enough to set classic Geiger counters off.
As mentioned above, this tube withstands great abuse to its limiting values, this is thanks to the internal simplicity of construction. I have tried numerous low-powered (not to melt the tube, that’s why) high voltage drivers for experiments with this; ranging from single-transistor flyback drivers, AC-flyback multiplier supplies, to resonant DST-flyback drivers. With a great deal of experimentation, the maximum voltage in cold-cathode mode is something over 45 kilovolts DC at forward direction, while producing lesser X-ray output and heating the anode more, because of greater current draw.
A much better result is at reverse polarity (something over 40 kilovolts DC allowed, before sparks start to crawl along the glass base). This consumes less current and provides somewhat more soft X-rays to be detected. You can also see the cathode glow white hot. 🙂 Not a single damn was given, who would use a rectifier like this nowadays.
In forward polarity (regulated resonant HV supply). Glows more, emits less.
Unfortunately, the radiation output is not enough to make radiographs or anything somewhat interesting. I had prepared some intensifying screens and a camera set to a few second exposure (5 to 10), however despite setting all my Geigers off ticking and maybe some random photon particles, hitting the CCD sensor, were noticed in long-exposure photos afterwards (as random colorful dots, “bad pixels”), it was not possible to make x-ray photos this way.
To get some pictures from this setup, one would need longer exposures, like a minute or so, to a photosensitive film in a dark room, then developing it afterwards. But instead of doing this, I had already advanced to better X-ray setups at that time. 🙂
Measuring radiation intensity with an IT-65, in both polarities
Endurance test with low voltage, from a different supply – not enough to create X-rays
Notice the occasional Geiger counter ticks – just a slight deviation from atmospheric radiation.