I have been thinking about this for a long time. I remember the old CRTs that, when they reached the end of their useful life, parts were replaced and evacuated and returned to service. With the help of skilled glass craftsmen, the X-ray inserts were rebuilt (I still have them in use). I think it is a complex task and it only makes sense in the most expensive tubes (6 or more MHU), on metal tubes. I have not seen any forums where this topic is discussed, I have my impressions about the limitations but I would like to hear opinions on the matter.
That's an interesting thought. But I've never heard of such repairs (rebuilds) myself.
Many years ago we came across "soft" x-ray tubes in military (battle field) radiography sets. They were simple (fixed anode) tubes, but even then the government didn't go for the evacuation (re-pulling the vacuum) option. Not sure if the idea was even costed (probably not); instead new equipment - complete systems (of lesser utility) - was procured.
By the way, there was a time when x-ray tubes were still manufactured in the UK; I remember visiting the factory (fifty years ago now).
I doubt anyone would have the tools of equipment to enable such a task and ensure it would meet the required standard after the process.
I do remember (maybe 40 years ago) it was possible to replace the tube insert in the housing with a special kit supplied from the manufacturer.
These days returned tubes in their housings are stripped down to recover all materials and some parts are remanufactured for use in new products, if they pass strict criteria.
The equipment needed to manufacture, align, and certify a X-ray assembly is beyond anything that could be done in the field.
P.S. The same is true for digital imaging detectors.
I agree that it is not a regular or easy task. @Geoff I understand that not being a regular or standard procedure a structured system will opt for practical solutions. @MikeX even today in countries with a different economy we do this task (replacement of inserts and/or oil refill) @MikeX : I have tampered with direct digital panels due to internal 3V supply failure due to blown filter capacitor
Regarding the necessary equipment: wouldn't universities and their science laboratories have the resources to deal with this? As an individual, I have provided myself with a UHVac system (Leybold pump + Varian diffussion pump + Varian UHV ionization meter) and a pinch off (3/4"). I managed to evacuate satisfactorily, withstanding 80Kv of test. I have problems with my leak detector (Helitest) for helium. I use it to pressurize the system before evacuating. As for certifications: could it be that bureaucracy is blocking us from applying engineering? Perhaps engineering should extend its ability to find the fissure in the confinement of bureaucrats. I think that the day will come when the control agencies extend the agony due to the lack of provision of certified coffins.
Back in the day (late 1970's) I was thinking of re:- "soft" tubes; our (British) government would have had all the gear of the type you mention. I would have preferred to at least try to evacuate those simple tubes. They were rugged and very much "fit for purpose" when first manufactured in the 1950's. I have sometimes wondered what became of those old Picker field x-ray sets, which had been purpose-built for battle field conditions (multiple electrical supply options, simple - "three knob" - controls, foldable design, air-portable, able to be carried by six-men - in theory at least, quickly set up and so forth). My other suggestion was to find (and-or adapt) a more modern tube to fit. Again (for some never-explained reason) I doubt this was even considered by my "technical superiors" (retired army officers, in the main). Such decisions were taken at meetings (followed, no doubt, by a nice lunch) in London, at a level well above my pay grade.
Originally Posted by vitapablo
As for certifications: could it be that bureaucracy is blocking us from applying engineering? Perhaps engineering should extend its ability to find the fissure in the confinement of bureaucrats.
Of course ... how many engineers sit (doze) on the benches of our Parliament? Or how many ex-soldiers for that matter. I'm afraid we are "governed" (badly) by "educated idiots" who wouldn't know an x-ray tube from a washing machine motor. They rarely (if ever) innovate ... but find it easier to be seen to be "doing something" by adding layer upon layer of restrictive legislation. You know, "ban this, ban that" and so on. In short, they are not practical people.
Picker made a lot of those field x-ray units. In fact the whole history of Picker is very interesting ... as this .pdf records.
"Our" field units were very similar to that shown at figure 14 (although the tube itself was more like the one shown at figure 12).
Here's a clear picture (which enlarges nicely) of the unit (but without the folding examination table). As I say, the tube was a simple fixed (stationary) anode type.
You mention Picker, I didn't have Rx of that brand but I did have CT, one of them still in service. Wire wrapped circuit boards Or printed circuit boards with engravings (textual) "To Mary"
The image on the right shows the Watson MX4. Watson & Sons was later absorbed into the GEC empire (as was Picker, albeit much later), and it was the later (improved) GEC MX4 that was used as the basis of the replacement for the Picker field unit I have been referring to. I'm not sure if they kept the rest of the system (folding table etc.) ... others may know (@Malcolm) ... by that time I had been moved on (pushed out) to sandier pastures.
GEC MX4 manual and circuit (as used on the famous "Arborfield course" fifty years ago).
I'm not sure where Picker stands these days (if at all). There have been various "mergers and acquisitions" and associations over the years: names like Dunlee, Philips, GEC, Marconi et al - even RCA - all figure in the story.
Meanwhile, here is a dramatic YouTube video that stars the old Picker field unit ... not much ALARA or staff H&S going on there! Notice there is no mention of the associated "manual" processing tank(s) ... or the time it takes to dip the film.
Perhaps I should add that the x-ray tubes manufactured at the (long gone) GEC Medical factory at Wembley were made under licence from Machlett (a US company, of course).
These days, the site of what was the GEC Medical factory has become the usual mess (er, development) of warehouses, small industrial units, empty lots, car repair shops and so forth.
The once famous Hirst Research Centre (cavity magnetron, WWII radar etc., etc.) was also located there. Hugo Hirst was one of co-founders (along with Gustav Byng) of the General Electric Company (GEC) in 1889; both were immigrants from Germany.
Lastly (for now, at least) for anyone really interested in current (as in "nowadays" ... as opposed to "Amps") High Voltage techniques, all you need to know (and more) is nicely presented in a download available on the Spellman website (the 2024 High Voltage Reference Manual near bottom right).
For instance, see Section 4 starting page 41 for "Common X-Ray tube failure modes".
The Spellman document you refer to is very good. That is precisely the brand of HV chain in CT picker/marconi. Also Toshiba in modern versions of Aquilion and Alexion. I use a set of Spellman multipliers (from IQ CT) as HV source in my workshop. I have sometimes disassembled multipliers (removing the silicone packing) replaced capacitors and vacuum filled with curable silicone.
The section on common faults in x-ray tubes would be expanded with the case of the 7.5 MHU Varian tubes. Violent gassing with filament breakage due to oxidation. In some cases the symptom is an arc (a slight residual vacuum remains to allow ionization) and when trying to "recover" the tube the filament breaks due to heating in the presence of gases (When performing an autopsy I have seen deposits of blue metallic oxide in the filament capsule).
