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 Post subject: Radar CRT data
PostPosted: Oct Mon 30, 2017 2:29 pm 
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Joined: Nov Sun 22, 2009 9:21 am
Posts: 185
Location: UK
Not strictly Tv related I know but it is Crt related.
I have a aircraft weather radar indicator I'd like to convert to a video monitor (I know the phoshor is slow on these).
I'm struggling to find data on the Crt, its an english electric 1478E.
I managed to suss out the pinout, or at least I think so,
Pin1 anode
pin2 nc
pin3 cathode
pin4 isolated heater
pin5 isolated heater
pin6 nc
pin7 focus
pin8 nc
pin9 brilliance
I applied 6kv with a jury rigged lopty transformer to the final anode, 24v ac to the heater at 150ma, and 2 meg pots to focus & brightness from -200v, connecting the cathode to ground (not a negative voltage) gives me a trace (I'm using 3v ac on the magnetic deflection coils to avoid burning), 1st anode supply seems to be best around 200v.
I managed to burn the screen slightly probably because my anode voltage is too high or something.
I cannot find data on this tube anywhere, even the pinout.
Any info welcome, yes this is a brit tube, brit forums are not that good for this kind of thing.


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 Post subject: Re: Radar CRT data
PostPosted: Oct Mon 30, 2017 4:22 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 666
I'd keep a lookout on the bay for another tube with more readily available data. They come up on the bay once in a while, cheap.


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 Post subject: Re: Radar CRT data
PostPosted: Oct Mon 30, 2017 5:56 pm 
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Joined: Nov Sun 22, 2009 9:21 am
Posts: 185
Location: UK
Yes I've been doing that, however this is part of an instrument I want to get a crt operational on, so said tube would need to fit the case, that kinda makes it unlikely to happen.
I spose I could use an Lcd, but this is a vintage piece of kit and I want to retain its appearance.
The nearest thing I have is a Dg7 which is a 2" round, this is a 5" x 3", there is a orange filter on the front, that would disguise things a little however the Dg is green so I'd need to replace the orange filter too.

I dug out the Eht supply from the chassis, sussed out its connections and got it to work, I get an image with it, at the moment I have the cathode grounded and the 1st anode at just 12v, I get an image and focus/brightness works these 2 controls and wiring are from the original chassis I just connected one end of the pots to gnd and the other to -200v supply.


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 Post subject: Re: Radar CRT data
PostPosted: Nov Wed 01, 2017 2:27 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 9431
Location: Powell River BC Canada
Here ya go : 1478E

AKA CV 6229
CV 10470


Attachment:
EEV 1478 E    because we decided what we had then.jpg
EEV 1478 E because we decided what we had then.jpg [ 82.58 KiB | Viewed 825 times ]
Attachment:
EEV 1478E phosphor.jpg
EEV 1478E phosphor.jpg [ 13.87 KiB | Viewed 824 times ]

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Radar CRT data
PostPosted: Nov Wed 01, 2017 3:10 pm 
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Joined: May Fri 29, 2009 4:35 am
Posts: 1967
Location: Chicago, IL USA
Here's a full datasheet for a CV6229

https://frank.pocnet.net/other/ServiceT ... CV6229.pdf

Note that the heater voltage should only be 19 VAC at 100 mA, not 24 at 150.


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 Post subject: Re: Radar CRT data
PostPosted: Nov Thu 02, 2017 11:27 pm 
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Joined: Nov Sun 22, 2009 9:21 am
Posts: 185
Location: UK
Wahay, thanks guys I knew I'd have more success here.
Radiotechnician thanks very much for that, the info is bob on, I found empirically the pinout (much to my surprise I got it right) and that the 1st anode works well at 100v (a bit high), cutoff voltage will be usefull as I want to make this thing digitally controlled on/off, thats just a matter of a mpsa42 and a voltage divider now.
Bob, also thanks esp for the heads up on the heater, I've watched probably too many of your resto vids, I dont have Tv's but I do half a dozen radio's some I have restored, 2 are US ones, a philco and a HMV.
Heres a pic of progress:
Attachment:
20171102_214554.jpg
20171102_214554.jpg [ 70.64 KiB | Viewed 749 times ]

Deflection is magnetic, the coils are fed from a stereo amp ic, and I managed to get the original Eht module to work, I realized with this thing having germanium devices that power isnt ground and +v, its ground and -v.
This info does present me with a little issue, my B+ supply is a smps and only regulates on the anode output, and I see anode is 70v max and brightness is -160v, loks like I need to mod my smps board, presently all outputs are from just one winding looks like I need a couple more, that or drop a load of volts to the 1st anode with a big fat resistor divider.


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 Post subject: Re: Radar CRT data
PostPosted: Nov Fri 03, 2017 2:15 pm 
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Joined: Nov Sun 22, 2009 9:21 am
Posts: 185
Location: UK
Ok I'll ask another question if I may.
The nearest voltages to the datasheet I can get for now is:
1st anode 100v
Cathode gnd
Bright, focus & second anode are as per the datasheet.
If I turn the brightness right up the sensitivity the deflection coils increases, I'm thinking this might be due to the first anode being around double what it should be voltage wise, the datasheet doesnt specify anode current, I'd like to use a pair of resistors as a divider to get the typical 1st anode voltage the datasheet states, however for this I need to know the 1st anode current, I spose I could measure it.


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 Post subject: Re: Radar CRT data
PostPosted: Nov Sun 05, 2017 4:04 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 9431
Location: Powell River BC Canada
I am puzzled by :
"If I turn the brightness right up the sensitivity the deflection coils increases,"

I would have expected the raster to shrink with increased beam current, since the
interaction is between the ampere turns of the yoke and magnetic field of the beam.

On old television sets a weak EHT rectifier, makes the picture bloom, i.e. get wider
and higher , and dimmer.

And as the CRT ( cathode) ages, bizarre effects, negative picture.

Happily the beam acceleration voltage 'magnetic' aspect is glossed over since I vaguely
recall that leads down a rabbit hole involving.....relativistic........

Attachment:
Magnetic deflection r.jpg
Magnetic deflection r.jpg [ 137.64 KiB | Viewed 662 times ]

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Radar CRT data
PostPosted: Nov Mon 06, 2017 4:31 pm 
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Joined: Nov Sun 22, 2009 9:21 am
Posts: 185
Location: UK
One thing that has occurred to me that could make this happen.
My bench supply could be current limiting dropping the supply to everything except the filament which comes rom another supply, so the Eht supply, B+ supply and deflection amp would all have reduced voltage if limiting where to take place.
My bench supply shows just over 1 amp, and its set to 2a limit so it shouldnt be happening, however in the past I've had it where current peaks have not made the meter respond but the supply has gone into limit mode to limit them and the voltage has dropped.
I dont think this is happening, however I havent checked supply voltage, so I'll do that.
Probably more likely is the Eht generator box is being fed the wrong supply voltage, I dont know what its sposed to be, and I dont have a hi voltage probe to measure the output, all I know is that the pass transistor regulator for the Eht supply module has a rating of 20v so its lower than that, currently its powered from 12v.
From what you said then I'm looking for a drop in Eht for the deflection to be more sensitive if the problem lies with the Eht.


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 Post subject: Re: Radar CRT data
PostPosted: Nov Tue 07, 2017 12:58 am 
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Joined: Nov Sun 22, 2009 9:21 am
Posts: 185
Location: UK
Further developments.
I realised I'd had the brightness grid down at a few volts neg, this is where I can get the highest brightness, however the control works kinda funky.
So I turned it all the way the other way, to near -200v now I get good control of brightness, and the focus control works well too.
This seems like the tube is working proper.
The Eht current has gone down a little, and its making a faint audible noise, and I can smell a little ozone (the anode cap is rotted away).
I have to admit I'm not that knowledgeable on picture tubes.
The other thing is my 'line' is more a series of dots, but thats going to be the smps built on bread board.


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 Post subject: Re: Radar CRT data
PostPosted: Nov Tue 07, 2017 4:10 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 9431
Location: Powell River BC Canada
Bandersen has posted a link to the complete specs to the CV6229.

It is important to protect the heater-cathode voltage below max.

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Radar CRT data
PostPosted: Nov Wed 08, 2017 6:10 pm 
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Joined: Nov Sun 22, 2009 9:21 am
Posts: 185
Location: UK
I think I have it sorted now.
There are 2 voltages on the brightness grid where I get a visible trace, 0v to around 4v, and -200v to -250v, the former is where I get this issues where the trace height varies with brightness, the latter works ok without the trace height changing with brightness.
Having the brightness near ground is obviously operating the tube outside its parameters and causing issues, probably secondary emission or something.
Moving onto deflection and graphics generating code next.


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 Post subject: Re: Radar CRT data
PostPosted: Nov Wed 08, 2017 11:22 pm 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 9431
Location: Powell River BC Canada
The low grid bias 0-4 volts might a zone where electrons are being ripped
directly from the cathode instead of the space cloud. Destructive !

CRT restoration is done this way, to possibly re activate a tube
to get a few more months life. The current is pulsed for a few seconds,
then the tube is retested for emission.

_________________
de
VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject: Re: Radar CRT data
PostPosted: Nov Thu 09, 2017 2:33 pm 
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Joined: Nov Sun 22, 2009 9:21 am
Posts: 185
Location: UK
Oops better not run it like that again eh.
I've seen Bob rejuve crt's, but I didnt know that was a way of doing it, I guess too long = no more cathode.
I dont have a tester, however I can get a very bright well focused trace so the tube isnt dead, how long its going to last I dont know.
Obviously I havent ran the thing that bright for more than a couple of seconds.


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 Post subject: Re: Radar CRT data
PostPosted: Dec Fri 01, 2017 7:07 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 17987
Location: Warner Robins, GA
The best way to keep the ehater cathode voltage within limits is to power the heater from a transformer putting out the proper voltage and tie one heater terminal to the cathode assuming neuither heater terminal has a path to ground.

That way both are always at the same potential.

That's how its usually done at least in oscopes which uses an electrostaticaly deflected CRT.

Quite an interesting project.

Far as video is concerned the decay rate of the phosphor might be too long, but it should be ok for displaying text.


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 Post subject: Re: Radar CRT data
PostPosted: Dec Fri 01, 2017 11:32 pm 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 9431
Location: Powell River BC Canada
The phosphor was made for airborne radar and was described 'low jitter'

_________________
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VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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