The 7290A is really compact, my 7290 is massive compared to that! The 7290 does have a shielded preamp however, but I guess they discovered they could do without.
As your 7290A has seen not much use, I would be very interested to see a short movie where you wave in front of a soldering iron or similar. This way we can see what is achievable from picture quality / speed with a almost new N2606 tube.
_Wim_,
I am not set up to record and upload video at the moment but will find one of my USB video capture units and sort something out for you soon.
Fraser
The Electrophysics 7290A is being rehomed with a good friend on this forum so it is going to a deserving home. I will be testing it, hopefully tomorrow, and will make a short video of the image lag available to those with an interest in such. At least this nice camera will now get some use rather than sitting ‘collecting dust’ in my spare room
Fraser
A little update on my 7290 non-A:
I've put maybe 15-20 hours of runtime into the unit since my oscillator fix and initial testing, and I've been trying to maximize image quality in software by boosting contrast and reducing brightness and gamma (high black levels seem to reduce the overall dynamic range of the image). Today I got enough of my new capture setup working to give it another test, and while I'll post in the other thread when I can document it, a dedicated SD capture card does wonders for black level and visual resolution over a USB dongle, I also took off the cover again to tweak some image parameters and sure up the aspect ratio.
I had noticed after my initial adjustments that on the right side there was a band at the edge that was very clearly imaging but that was darker than the main part of the image, and on the left side the edge seemed to fringe towards white output despite being within the limits that would fit in the circular aperture captured when you decrease H size and V size enough to see it. I adjusted the H size to cut off more and recentered it, then adjusted the black and white levels as well as the setup voltage to give better contrast and evenness in similarly lit conditions.
It was then that I turned off my SWIR light source and noticed I could still see some image.... but in reverse. I think I've managed to burn in my tube slightly, but while I'm probably going to play with the target voltage a bit to try and adjust things, I was wondering if anyone knew if overdoing and adjustment could effect burn in. The amount is small, it's only really visible with lights off, and it's on the static elements of the frame that are reflective and fairly brightly lit. The burn in is a negative of the image captured, so I wonder if exposure to strong sources could actually help reduce the total effect - with the notable exception of a nixie clock in frame, which also has the display visible after power up and with dark over the frame, but these appear bright as if lit when no light is actually exposing the tube.
In any case, it was a bit alarming to notice after such a short use, so I'm going to see what I can do to reduce any further effects. I left my target voltage and high voltage on middling settings to try and avoid issues, but perhaps they are still set too high even though I don't believe I'm achieving the voltages on the silkscreen.
Burn-in was a problem with visible light vidicons so I suspect it may also affect IR tubes. Most minor burns seem to sort themselves out over time (days) but some can be permanent. Back in the say I had a friend who bought a 'new' colour video camera based on vidicon technology and was dismayed on using it that there was a burned-in image of the shop window, where it had been on display all summer and showing passers-by their fizzogs on TV.
I seem to recall that you can - with care - run a vidicon with abnormal voltages for a short period of time and in many cases reverse, or at least reduce, minor burn-in. Bill may know something about this, otherwise I'll have to call upon the memory of my friend who bought the dodgy camera (we're still in touch, occasionally, knocking on 40 years later).
I concur with what Ultrapurple has said. The SWIR Vidicon behaves similarly to a conventional visible light Vidicon where ‘burn-in’ is concerned.
Burn-in occurs when the imaging target is illuminated with a bright scene for an extended period of time. This is usually days rather than minutes or hours. If a very bright source is left within the cameras field of view for an extended period of time, accelerated burn-in can occur.
In normal use a Vidicon can be moderately overloaded at the target face and suffer temporary latent image retention. The same occurs with a bright scene that is static in the field of view for many hours. This phenomenon is not damage to the tube target, it is just image retention and the target will equalise itself when the scene is changed or the camera left running with its lens cap in place for a while. It will also correct itself over time with the camera switched off.
Vidicon tubes do demand some respect in terms of exposing them to very bright energy sources but they are not as fragile as some may think. You have to work pretty hard to wreck the target in normal use. These SWIR cameras are designed to tolerate exposure to a relatively bright collimated laser beam hitting the target of the Vidicon via an appropriate ND filter and no lens. They tolerate such use without permanent burn-in.
The enemy of the. Vidicon is a static scene viewed over a long period of time. The common use of Vidicon tubes in CCTV demonstrated how a scene could be burnt into the target over a period of a year. This applied to both exterior and interior static mount CCTV. It was not unusual to fit new Vidicon tubes in static CCTV cameras once the burn-in became noticeable to the users and distracting. Vidicon cameras mounted on scanning mounts that moved the camera slowly in the horizontal plane did not suffer the same burn-in effects but would suffer ‘hours run’ deterioration in the image as they were operating 24/7/365. Such was to be expected in a CCTV system that uses the technology and the viewing monitors could also suffer from burn-in if constantly viewing a static scene.
I would advise against exposing the 7290A cameras tube to pronged viewing of a very intense light source without the camera moving to avoid over exposure of a defined area of the tube target. You do not need to wrap these cameras in cotton wool though ! Never be tempted to directly view an incandescent lamp of decent power, especially a halogen lamp. Such will risk damage to the target. The lens IRIS can reduce the intensity of the scene to help protect the tube but a ND filter is a better option.
Fraser
Probably a stupid question, but are you sure it is burn-in (in other words did you test with moving something in front of it in the dark scene)? I have seen the image reversal on mine by the auto-gain overdoing the target voltage to try an compensate for the darker scene.
Fairly sure, I went through a bunch of adjustments again today and think I got things working a bit better, slightly less image lag, and a bit more even field - I see a good bit of vignetting around the edges of the image, so I was trying to reduce it a bit.
Adjusting the target voltage had a pretty wide range where the image looked alright, too high increased vignetting, too low and eventually the picture drops out. I ended up a bit above previous and it is a bit faster.
Adjusting the beam pot also seems to move around the center point of the vignetting - the darkest black on the camera - and you can move it back and fourth horizontally a bit. I found that very low beam levels were just no image, but there was a zone on the low side of the setting where the image appears in inverse, then a bit higher and it rights to the normal colorization.
I could also adjust down the main voltage a bit and still have a good image, but I found that a bit of scan-line type of slightly off sync noise resulted in being off of the setting I eventually settled on.
Good to hear about the potential time scale for burn in, I'm nowhere near that, and while I was definitely seeing the previous image after a cold boot the next day, after adjusting the settings today, I'm not really seeing the image that was there, so I think it was a combination of the long-term image retention and the gain/contrast settings being boosted and showing that last residual bit of charge.
I think it's worth noting that the timescale for burn-in previously noted is for a 'normal' scene. Permanent damage can be done instantaneously by a gross overload (such as directly viewing a laser beam or, as has been mentioned, pointing the camera at an incandescent lamp).
I managed to get another one of these cameras working, this time a 7290A, and in my experiments and image tweaks have developed a basic starting procedure as well as a couple of tips/things to check if you're having image trouble on your unit. I haven't worked with any other vidicon devices, and the silkscreen labeling can be somewhat inconsistent between models, so it took more trial and error than I had expected, but I've at least got a reasonable procedure.
When trying to get image out of a camera that you know is working, my first port of call is the 300V adjustment, just to verify that the 300V cap (and the various other voltages devised from the same boost converter) is biased at the right amount. This also effects the target voltage, so it's worth messing with first. Then, I measure the target voltage on the board and set the corresponding pot to 10-15V. In my limited experience these tubes will produce an image at lower voltages still, especially in the visible band, but with reduced sensitivity and it's useful to have a lower starting point to adjust later. Some cameras seem to have their tube's target voltage marked on a sticker, but this isn't always present and I've found it's not really required.
From there, we want to verify basic imaging, which is basically making sure the tube is actually reading out usable information. When powered up, the camera should spike slightly, then gradually decrease current usage after the high voltage biasing is charged up. The screen will go white after generating the sync signal, then dark (or potentially reverse) and in a few seconds the screen will sort of fade into an image after that point, usually in a sort of spreading puddle shape and sometimes including some wavy horizontal lines (more on that later). The 7290 (non A) I have takes longer to start the image fading in, but this could very well be due to aging components, as it actually takes my 7290 a couple of minutes to stabilize at full image size/correct rotation/no flickering - I just haven't bothered to track down the responsible components. The 7290A I just worked on will get an image in less than 10s from power on, but it goes through the full screen cycles then fades into the image, even with a well illuminated scene.
From the starting target voltage set, I adjust the black level pot (if the lens is facing towards you, it is the second to top potentiometer facing upwards on the left hand board) so that it is an in-between setting, then I adjust the potentiometer on the vidicon base's board (the one on the left side of the board when both pots are facing up and the lens is pointing towards you) and test to see if I can see motion in the image. Once you see motion, it's all about trying to maximize that signal, this usually involves some turning down the black level to be darker, but also turning up the target voltage slowly. More target voltage means more sensitivity and less ghosting, but too much will make the image go fully white and then, if pushed farther, fully black, and running too high can damage the tube. I like to start low and gradually increase the level until I can notice the image ghosting decrease - there seems to be a region where a little increase in voltage makes a notable change, and at a point it stops being noticeable. It is important to mention that light will leak in from the sides and you want to be setting this level as close as you can to usage conditions, so inserting the filter holder (to block some stray light) or just turning off bench lights to work with a minimum to see the adjustment pots can be quite helpful. If you're looking for SWIR or NIR only bands, it's also worth putting in that filter, so that if your target is brightly lit in visible, you don't end up setting the brightness too low in the band of interest. It is best to do these adjustments with the lens mounted and with a target that is high contrast.
Once you have good contrast on your image, you want to focus it, using the focus pot on the right hand board and the pot on the right hand side of the tube base board (again with the lens pointing towards you). I try to focus the lens as sharp as I can get, then adjust the focus pot to as sharp as I can get, then treat the right pot on the tube base board as a fine adjustment for it, since it has some similar effect on the image. This usually has to be repeated, and don't worry if the image isn't plumb. At this point I move to the horizontal and vertical adjustments on the right hand board to both try and center the image in the lens aperture (you can see the circular edges when the deflections are maxed), fill as much of the aperture as possible, and stay away from any bright or dark spots that track with the movement of the position adjustments. Remember that with the image persistence it takes a few seconds for the image to settle, so it's best to adjust, wait a second, then check, rather than try to operate in realtime.
At this point I turn to the four pots that are outward facing on the left hand board and adjust them for as even a field illumination as possible. Proper adjustment of these should cancel almost all vignetting at edges or bright/dark regions of the screen, and you can usually adjust them by watching the bright band or dark spot move around on the image and just try to null it out. At this point if your image is off the vertical axis, loosen the four small set screws that are holding the metal sleeve around the tube and gently rotate the tube in the required direction. This is best done in small increments, while power is off, and then repower and wait for the image to check your work. No need to be sticking your hands on the tube when it's biased at a few hundred voltages and the whole assembly is pretty sensitive to vibration and EM noise (coupled in by your hands, metallic tools, whatever). That basic process takes a bit of time, but has yielded good results for my image quality and can be started basically with unknown settings.
Now a couple of quirks of the design that I've realized and which could be helpful:
First off, if you have your basic voltages set, you think the electronics and tube work, but are seeing no image (and not the normal dark and white transitions that then fade into an image on power up), your tube could be the wrong distance from the lens mount. Basically, the glass tube itself can move inside the metal sleeve with the deflection coils that is anchored in place, and if the tube face is too close to the lens, it will be far enough outside of the coils for no image to appear. You can gently press on the face of the tube with a clean cloth to slowly press it farther in - in my case a millimeter or two behind the metal bracket that retains the filter mount - to make the tube set back farther in the coils, and this should get your image. Distance to the lens also effects where it can focus so it's worth testing the full range of the lens to find a good place for it, but if you need to reverse the direction and move the tube towards the lens, gently press and rotate the board on the back of the tube. The direction of rotation is not important because the image will be aligned from the coils around the tube, but turning it too far could cause access issues for the cables or to the pots.
Another thing to be on the lookout for: if you see wavy horizontal lines that look vaguely like scalloped cracks... these are not cracks. I haven't actually figured out what they are, but I've now seen two tubes that with more adjustment (and some of this is tube position in the coil dependent), even when these lines are visible at the first power on image, they go away and the image can look normal. An artifact of the scanning, I think, maybe someone can shed some light on the phenomenon.
Finally, the image is read off the tube through the light blue wire at the front left of the tube, into a SMD JFET on the inside face of that left board. Getting your hand or tools near that cable will couple in noise that is visible on screen, and leaving the screw out of the nearest mounting hole can cause grounding issues that give you a lot of garbage on screen.
I've got another 7290A to work on that's just not able to run its boost converter for more than about 2 seconds for some reason, but I hope to test out the adjustment method again on it, which has basically the same parts and layout, but earlier board revisions with several alterations not seen in the unit I've now got working. Expect to see a comparison with the 7290 (non A) at some point too, the 7290A definitely has less of a vignetting effect, but it also could be the age/condition of the electronics.
Excellent work 👍
The Vidicon tube is an orientation sensitive device with regard to its installation in the deflection coil assembly. From memory the data sheets provide details.
Fraser
The 7290 (non A) I have takes longer to start the image fading in, but this could very well be due to aging components, as it actually takes my 7290 a couple of minutes to stabilize at full image size/correct rotation/no flickering - I just haven't bothered to track down the responsible components. The 7290A I just worked on will get an image in less than 10s from power on, but it goes through the full screen cycles then fades into the image, even with a well illuminated scene.
Wow, thanks for this very detailed description!
My 7290 (non-A) starts up in approx. 15 seconds, so a couple of minutes start-up is indeed probably related to some aged capacitors somewhere on the board.
I maybe should record the turn on sequence... it's really something. The image starts too small at the center of the screen and twisted, and gradually extends and untwists until it's full size. There's also an intermittent flicker that looks like the picture losing lock or something that is every few seconds right at the first image being displayed, but which works itself entirely out after a couple minutes powered on.
Now that I'm thinking of it, that's a very similar initial behavior to the function of the focus adjust pot, so maybe it's a capacitor or something on that line or something that doesn't work as intended until it's warmed up.
I maybe should record the turn on sequence... it's really something.
You know we all love pictures and video's...
Hi, does anyone know what is the voltage for the power supply of Electrophysics 7290(non-A) version? I have one that has the exact same board as in the figure in Reply#78 but without the power supply. I assume it is AC as it has a bridge rectifier BR805D? Thanks in advance!
I believe it will run on 12VAC, but give it 12VDC and it should be fine. Mine runs on 12VDC from the power connector, around 10W in total. We believe the rectifer was for a version of this camera that may have had a different application or tube, and I think it would be still possible to supply it from AC (at least connecting directly to the board) given the rectifier.
I now have the user manual thanks to excellent support from Sofradir in the USA
Fraser
I know this is an old post, but I have a request directly related to that post. Could you possibly scan that manual and post a PDF of it here?
Thanks. I downloaded it now.
In the document I see the gamma is 0.7, is it possible to set it to the normal 0.45?