Michael, A couple of points.Normal background radiation is very weak. If you are only reading a 15% increase over background levels, either your tube is not emitting much, or your detector is not sensitive enough to the X-rays you are producing, or you are seeing RFI from your HV source instead of X-rays. If you are really making and detecting X-rays, you should see a 100 or 1,000 times increase in your readings.
Technically, your high voltage supply is not a Tesla Coil, despite the label on the front. It is more akin to an SCR driven auto ignition coil, much like the old fashioned induction coils, which were driven by a mechanical interrupter. It lacks a resonant tank circuit coupled with a secondary, so it's not really a TC, but is is still a high voltage source. The switching transients of the SCR interacting with the primary coil will generate RF interference even if no current is flowing through the secondary.
Both of your detectors are probably going to be sensitive to the RF emitted by the HV generator. Do you see a change in their readings if you power up the system with all wires in place, but a gap in the circuit so that no arcs form, or any secondary current can flow? If so, then you are measuring RFI instead of detecting X-rays.
To achieve X-ray emission, you need extremely good vacuua, something like 10^-7 torr. Achieving ultrahigh vacuua like that requires specialized equipment and difficult techniques.
I would stand by my previous suggestions, and see if your X-ray detectors are actually detecting when exposed to a known X-ray source, like your friendly dentist's X-ray machine. It is also entirely possible that neither of your tubes has a good enough vacuum to produce X-rays. If the tubes are up to air, it is possible that the spacing of the electrodes is great enough that your HV generator cannot arc across them, so they would appear as an open circuit.
I would also look for a used medical X-ray film cassette. These should contain a white plastic phosphor sheet that will fluoresce green or orange in the presence of X-rays. They should give an obvious visible indication of whether you are actually producing X-rays or not.
An old 1B3 high voltage rectifier tube from a vintage B&W TV will also produce x-rays, and should cost only a few dollars. They are usually available at Hamfests or on eBay for a low cost. If their getter spot is still silver in color, their vacuum should be good, and they should radiate if supplied with high voltage.
Several years ago, in a conversation with George Dowell on the Geiger Counter Enthusiasts list, he indicated that X-ray tubes actually radiate more energetic X-rays if their filaments re NOT energized. With hot filaments, less energy is required to liberate electrons from the cathode, so the resulting X-rays are lower energy. Crookes' original X-ray tubes did not have hot filaments.
Dave On 1/27/2018 4:18 AM, Michael Loundry wrote:
Thank you Dave! I agree in all points with you. I have made also a tests with Flyback 15KV from CRT. DY87 tube was giving approx. 15% more counts than with background. There is just blue glow visible. TRX708 tzbe was not giving anything. No glow visible at all. Some time ago I have made my own vacuum tube that was made of stainless steel tube with a rod in the center. This gave 10x background with the Flyback. All tubes are giving just RF similarly as with a rectifying diodes. Which tells me that it is doing something. I have to admit that all detectors are sensitive to RF to some extent. So it could add counts or even decrease. But it is again in a very small range (5 - 20% change) But still I can see Energy spectrum of all counts. And there is never characteristic X-rays visible. The RF from the Tesla Coil is so strong that all nearby electronics is failing. So it would be good to shield it in some way. I am sure that TRX708 tube has no air inside, since it is behaving all the time as perfect insulator. The Tesla Coil is producing humming as if there is too big gap (no current is flowing) however I connect it. If there is a short or at least some current is flowing the sound is very different. I have tried to measure filament emmisivity and I can measure voltage between Anode and Cathode when only filament is under power. So I am pretty confused because with both HV supplies it looks like there is no electron flow inside with the TRX708, thus no circuit. Both Flyback and Tesla Coil have no current flow between Anode/Cathode. So the vacuum is pretty good I think. On the other hand supplier of the tube tested it with 70KV HV supply and is sure it is perfectly OK. But his DC supply seems to be much better. But why it is giving off RF if no current is flowing? I dont understand it. Probably the current is very, very small. I have to also admit that my Tesla Coil is not able to light up also any light bulb. There is just arc through the entire bulb or there is nothing (depending on configured voltage). No glow at all. This is reason why I think there is something wrong. Ends from the secondary are so that one is touching filament and second end is at the top of the bulb. My tesla coil is not grounded and that is probably reason since I know that with other Tesla Coils I have saw it arcs everywhere inside the bulb just by touching one end. But probably everybody is grounding the coil which is what I dont wish to do. I have full schematic of my Tesla Coil so you can look at this: https://ibb.co/gWyZgw By the way it is fully shielded with 3+ mm of Pb so that nothing can escape. Also time that it is running is just few miliseconds. Does it make any sense for you?Sent: Friday, January 26, 2018 at 11:54 PM From: "David Speck" <Dave@xxxxxxxxxxxxxxxx> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx> Subject: Re: [TCML] Tesla Coil and X-ray tube Michael, According to this table: http://www.sciencemadness.org/talk/files.php?pid=400982&aid=38982 your 9 cm arc between sharp electrodes should be indicating about 70 kV, which should be enough to make X-rays. Even without external rectifiers, an X-ray tube is capable of operating in self-rectifying mode on an unrectified AC source. It would produce a lot of unwanted, scattered radiation on the reversed biased part of the cycle, but it should still produce plenty of X-rays when forward biased. Have you checked for X-ray output with a foolproof X-ray detector like an X-ray sensitive phosphor sheet from a medical X-ray cassette? Have you been able to see any faint green fluorescence of the tube walls during operation? How can you be certain that your X-ray detectors are working properly? From what I've read on the Geiger Counter Enthusiasts Usenet groups, ionization chamber radiation detectors are the preferred devices for detecting and measuring X-rays in the energy range that you indicated. In the circumstances you describe, I would speculate that either your tubes are up to air, and not producing X-rays, or that your detectors are not working. See if you can find a sympathetic dentist to direct his X-ray machine at your detectors to be sure that they are actually working. Typical dental X-ray machines run in the 88 - 100 KV range. Be careful. 70 KV X-rays will produce a substantial skin dose while being imperceptible. Dave On 1/26/2018 8:20 AM, Michael Loundry wrote:Dear subscribers,I have recently bought Tesla Coil with adjustable output voltage 5 - 100kV.It is driven by thyristor (SCR) circuit and powered from the mains. Tesla coil itself is in mineral oil. Secondary has both ends available from the plastic case, so there is no grounding. It is this unit: http://i.ebayimg.com/images/i/311006967911-0-1/s-l1000.jpg The Tesla Coil seems to be powerfull enough - can produce a lot of ozone, arcs can be at least 90mm long. Input power is around 200W.I would like to ask you, if you think that with this Tesla Coil I should be able to produce X-rays? What I have?- Proper lead shielding - NaI 2.5x2.5" scintillator probe with sensitivity for 15keV - 3MeV - Additional Geiger Counter with sensitivity from 50keV - 3MeV - X-ray tube Trophy/Kodak TRX708 - Vacuum tube DY87 - 20x rectifier diode for 18KV, 20mA (can be connected in a series)My goal is to produce X-rays, but unfortunately I am not able to do so in any case.Both X-ray tube and vacuum tube are basically new and verified to work.What I have tried:1. Heating filament with AC/DC to nominal current/voltage for maximum electron emmisivity. 2. Connecting TC to Anode and Cathode. 3. Changing TC polarity on the panel (this is swapping live/neutral for the primary side). 4. Using rectifying diodes so that output is pulsed DC. 5. Swapping Anode and Kathode wires. 6. Tried to change filament voltage from 0 to max allowed. 7. Tried same procedures with DY87. 8. Tried it with arcing (wire for cathode had a small gap to create arcs).Of course collimator from the X-ray tube is positioned parallely to radiation detectors. What I was able to produce was just RF in some cases. Could you please let me know what could be wrong? Why my Tesla Coil is not producing any X-rays? Is some grounding required?I know my meters can pick X-rays pretty well. 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