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Radar CRT

Discussion in 'General Electronics Chat' started by dr pepper, Oct 24, 2017.

  1. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    I have a vintage weather radar indicator, and would like to see if I can use the CRT as a graphics display in one of my weird projects.
    Its a EEV 14788E, the indicator is made by ekco a well known Uk manufacturer, of course no data is available.
    These units where used in military, commercial and private craft.
    I can see from the base the heater connections, some idea of voltages etc would be a good start to test this thing, the high voltage box appears dead and its potted.
    I've been trying to suss out the boards, it has tranny's but they are geraniums, the X/Y deflection is magnetic so shouldnt be so hard to get working. 20171024_192304.jpg 20171024_192318.jpg
     
  2. alec_t

    alec_t Well-Known Member Most Helpful Member

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    You may well find that the tube has a long-persistence phosphor. Would that be a problem for displaying your data?
     
  3. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    I'm just playing with it for now, a break from more pressing things, dont realy have a use.
    It doesnt say what the phosphor is, like you say it might be a P1 long persistance instead of P4 found in telly's.
    The unit has a marker video amplifier board and a sweep generator + amplifier board, so the beam is obviously swept on the screen, I think it will sweep from the bottom outwards in an arc, there are rings slightly burned into the screen I suspect these are something to do with the marker board, I think this generates range markers depending on selections.
    I can if I find some high value high voltage resistors put togther an Eht supply from a more modern lopty from a telly using a uc3842 or mc34063, done that before.
    The filament is probably 6.3v but there are some odd ball ones that are 2.3 & 2.6V, screen & focus are going to be the tricky ones to suss out.
     
  4. dave

    Dave New Member

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  5. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    Ok I found an old prototype board I made a while back, for a 'scope tube, it generates all the required voltages for the tube however I remember I used a tube that doesnt need a high anode voltage, just a few hundred volts, I think I used a Tl494 and a ferrite transformer.
    Another couple of ideas came to mind, I can trace the wires from the high voltage supply, I wonder if the heater voltage comes from it, also there is brightness & focus on the front panel, those might also go back to the Hv module/Crt.
    Another thing I noticed is that the fan on the back is 110v, so the 28v label on the back probably means it has 110v ac and 28v dc, so the Hv module probably runs from 110v ac, I was using 28v, probably why nothing happened.
     
  6. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    Had some success.
    I found the original high voltage supply had a pair of outboard trannys, so I connected these up, but still cant get any output.
    So I pulled apart a 5" cheap chinese b&w Tv I have lying around, nicked the Eht from it (just a croc clip jumper lead), then dug out my old 'scope clock power supply board which generates 350v 1st anode voltage as well as focus & screen voltages with control pots. It seems the filament is 24v, so I powered that from another bench supply.
    And I get a dot, but not for long, the dot appears then goes at power on, so I assume the voltages might be a little too high, the 1st anode supply has a soft start and as the voltage comes up it must be going through the operating voltage of the crt. I tried leaving the Tv powered up so its eht was present all the time, then cycling the power on the 1st anode supply, the problem is the same so it appears that its not a problem with eht but too high 1st anode voltage.
    20171025_203227_001.jpg 20171025_203313_001.jpg
     
  7. JimB

    JimB Super Moderator Most Helpful Member

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    Experimentation - I love it!

    And your sig-line seems so apposite to that picture.

    JimB
     
  8. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    I managed to make a little improvement, I noticed theres no dag on the tube, so it probably needs a smoothed eht, so I paralled the radar crt with the one in the telly, ie used the telly's crt as a smoothing cap, the dot is now more defined.
    However I'm surprised it works at all, throwing it together in a hurry I forgot to connect the cathode to negative, right now its grounded, I think I have the focus & brightness pins correct as those pins go to pots in the radar display, the heater looks as though its independant its not commoned to the cathode.
    So I'll rewire the thing so the cathode is negative 200v and see what happens.
    My 'scope clock Dg7 crt was fuzzy & out of focus with dc on the heater, this tube seems fine with dc.
    Gonna point a Geiger counter at this thing & make sure i havent got the eht so high I'm x raying everything.
     
  9. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    I am not familiar with British radar at all; however, that tube looks like what a vintage King KWX50 radar might have (monocrhome, 4 levels of intensity). Have you looked for a free manual? If it was from a KWX50, the manuals on eBay seem to be $11 USD or less.

    I recently did some reverse engineering on an ADF by King (KR85) . Some vendors ask outrageous prices. I found a free download.

    John
     
  10. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    Ww2 electronics from what I've seen is similar between us brits & the Us.
    I looked for the manual for the KWX, unfortunately the net is swamped with those wanting to rip me off and finding a free one isnt easy, however I did find a pic of the Crt from within one, and it looks very different.
    I must have the connections something like correct to get the dot, so its a case of more experimenting, I can see most of the internal grid connections on the gun so that plus some googling for Crt gun pics ought to get me a bit further.
    One thing about brit military items looking for any data is just a waste of time.
     
  11. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    Well got home from work, and before bed had another play.
    With negative bias on the cathode, which is a seperate pin from the heater the tube lights up, not quite focused but my makeshift focus pot does have an effect.
    With Ac applied to both deflection coils there is a lissajous pattern, I expected a straight line, but I spose the field strength of x and y field coils isnt going to be exact with the same Ac voltage drive.
    Looks like I now have the pinout sorted, I can build a regulated Eht supply Ok I need to find a way of measuring what the little Tv's eht is, probably around 5 kv.
    Then its on to deflection amps, shouldnt be hard, the Ac voltage applied in the pic is only 3v and its way off the screen, so slew rate and voltage swing shouldnt be an issue here.
    20171026_070427.jpg 20171026_070612.jpg
     
  12. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    Got the beams to focus & brightness to work.
    Some odd things going on though with this tube, I had the 1st anode at +200v and the cathode at -200v with focus & brightness not connected, no beam.
    Then put +400v on the 1st anode and 0v on the cathode, no connection to focus & brightness, this time a beam, then connecting the focus & brightness pots between -200v & ground I got those controls to work too.
    I fail to see the difference between having the cathode at -200v and the 1st anode at +200V than the cathode at gnd and the 1st anode at +400v, ground isnt connected to the tube so there should be no difference, the heater power is isolated, must be some secondary emission diode effect or something stupid.
    Anyway it works, just need to find a more permanent way to provide the eht, might pull the 5" b&w tv apart as I suspect the lopty B+ is 12v, all that'd need is a fet and a 555, might need to find a doorknob cap too as this crt doesnt have dag, or maybe spray it with some slip plate & ground it.
    Edit: Traced the wire back from the cathode, it goes to a Bfy50 which has its emitter grounded, so the cathode was only driven to ground not below.
     
    Last edited: Oct 26, 2017
  13. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    Hmm.
    I got the Eht power brick to work, it has geranium pnp trannys so the case is + not -
    However I noticed that the 1st anode resistor was getting hot, due to it dropping most of the B+, anyway I now have the tube working with the cathode grounded and 12v on the 1st anode, doesnt seem right but it works, and brightness/focus work too.
    I'm certain of the bright/focus pins on the tube as I'm using the orginal pots and wiring, the cathode was grounded through a tranny, the heater went to 24vdc the only wire I couldnt suss was anode, as it just goes to a pin on a connector at the rear panel.
    Doesnt seem right, but if I lower the cathode or raise the 1st anode it just pulls loads o current, right now as bright as it'll go the whole thing with its 2 inverter supplies burns 15 watts.
     
  14. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Very pretty :D
     
  15. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    Yes pink, red & blue.

    Oh and the Crt works better now, after a close inspection with a troch I realised I had brightness & 1st anode swapped, all works well now with expected voltages & even less power.
     
  16. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    Heres another pic, sine waves!
    B+, B++ and Eht all work now, and pinouts are sussed.
    I put together a deflection amp from a stereo audio amp chip, bandwidth of the amp ought to be enough it has good Gbp and slew rate, however I'm not sure if the field coils will work, as they drop off at 1Kc, maybe if I change the feedback on the amp so that it becomes a voltage controlled current source it will greatly improve, esp if the supply is 12v and full deflection is 2v.
    I'm not sure what bandwidth I'd need for vector graphics, I'd guess about 10Kc.
    There are 2 waves on the screen as X is driven with a sine wave without blanking, and of course theres no trigger.
    The amp Ic is a Tda7265, there is a bit of weirdness the amp will not power up unless I make mute/power on active for a while (shutdown) then deactivate it (power up), maybe I need an r/c to pulse this pin on power up, the datasheet doesnt mention anything, just that its processor compatible.
    20171102_214554.jpg
     
    Last edited: Nov 2, 2017
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  17. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Somehow my post didn't post. Here is goes again...

    Good work. That's exciting. All of the monochrome radars I have seen in the US* were shades of green on dark. Can the color be adjusted or is that a set property of the phosphor?

    John

    *Edit: Just King and Bendix stuff from before 1990
     
    Last edited: Nov 2, 2017
  18. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    If you look at #10 the colour is the same, there is a filter with range markers over the tube in the housing but the colour is the same as the bare tube, sort of an orange.
    The only 'proper' experience I've had with radar is from a furuno low range set, I wouldnt call 40 miles low range but I spose these days theres no limit, I used to be matey with someone that was a radar man in the forces he is a clever chap, unfortunately moved away to scotch corner.
    I got a datasheet for the tube, a couple of knowledgeable geysers on the antique radio forum found it for me, theres another tube similar, apparently a CV6229.

    P.S. thanks for the like, the forum just gave me another award, maybe my boss is wrong I'm not a numpty.
     
  19. BobW

    BobW Active Member

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    Most of the orange phosphors are long persistence, making them suitable for radar applications.
    https://en.wikipedia.org/wiki/Phosphor#Standard_phosphor_types

    In my stash of parts I have a surplus 5" CRT that was part of some kind of aircraft instrumentation. Also a long persistence phosphor. Unfortunately, it's just the bare CRT, no power supply and no deflection circuitry. One of these days I may get some inspiration for a suitable project. I think I was planning to build a vector graphics display at one time.
     
  20. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    Thats why movies show orange on radars then.
    Early ww2 radar tubes were blue but short persistance, they were a scopes not the rotating kind we are more familiar with.
     

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