XY Monitor / Display

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Re: XY Monitor / Display

Postby Steve Anderson » Mon Aug 27, 2018 9:13 pm

Good idea Harry. One transformer 110V->12V then 2x12->110V with the 110 windings in series...if you get almost zero volts out reverse one (only) of the 110V windings. The input one can be 12V-0V-12V at say 1A. this will also provide the low-voltage supplies, the two output ones can be 12V-0V-12V at 500mA. The total load is quite light. If you go this way you'll still be needing that separate 6.3V transformer for the CRT heater. So that's four transformers in total.

The 5V winding on the 600V/6.3V/5V transformer if you go that way might be useful too - we'll see in time.

The 6.3V winding for the heater will be sitting at a high negative potential so it can't be used for the low-voltage stuff. All you requite is a 12V-0V-12V transformer at a hundred mA or so for the low-voltage stuff - quite small (cheap). A total of two transformers in this case.

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Re: XY Monitor / Display

Postby FlyMario » Mon Aug 27, 2018 9:42 pm

Ok so I think I have lost the plot here.

The transformer I showed with 600v,5v,6.3v... is like 3.5lbs. That must be a huge transformer. I have no plans on purchasing that thing.

I am happy to hear that 6.3v supply is going to be fine.

I guess I thought I was reading that basically, the 12v transformer would go into a voltage multiplier circuit to get around 600v. Which in my head would be like 20+ multiplier sets. So I am puzzled.

I think you guys are saying 12 to 240v transformer. So instead I would get a 120v to 12v transformer and a 240v to 12v transformer and use the 240v one in reverse to get 240vac out of a 12vac transformer and them multiply the rest of the way up? I don't mind that but I want to be sure.

My mains is around 120VAC.

As far as buying vs scavaging, when I was a kid If I needed anything I would grab a junk item and pull a cap, transformer or whatever. It's just right now I have so many hobbies that I can't just keep so much stuff around I could grab parts out of. I would be very embarrassed to show you or anyone the stuff I do have at it is.

Thanks,
Pete
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Re: XY Monitor / Display

Postby Harry Dalek » Mon Aug 27, 2018 11:59 pm

FlyMario wrote:Ok so I think I have lost the plot here.

The transformer I showed with 600v,5v,6.3v... is like 3.5lbs. That must be a huge transformer. I have no plans on purchasing that thing.


Ok so your not getting the big bugger transformer ,,then you have the next choice of either finding a valve radio transformer it would be useful if you can find one ...or the 2 modern 12 volt transformers for a back to back step down step back up idea

I am happy to hear that 6.3v supply is going to be fine.


As mentioned you can do the same thing with a few little transformers if there's a will there's a way :idea:

I guess I thought I was reading that basically, the 12v transformer would go into a voltage multiplier circuit to get around 600v. Which in my head would be like 20+ multiplier sets. So I am puzzled.


Here's my results for the Anderson 3bp1 monitor this gives you an idea .i forgotten what your tube needs but couldn't be worse than mine ! we have to have another look i am sure steve would check how many stages you need if you copy this idea ...its not to bad ..those load resistors will test your supply and drain the caps on turning off again always touch only with the multimeter ..have you got a HV probe ? need that most multi meters are 500v 1000v if you are lucky.
harrywashereoie_akIq1SaXseuT %281%29.gif
harrywashereoie_akIq1SaXseuT %281%29.gif (45.9 KiB) Viewed 2042 times


I think you guys are saying 12 to 240v transformer. So instead I would get a 120v to 12v transformer and a 240v to 12v transformer and use the 240v one in reverse to get 240vac out of a 12vac transformer and them multiply the rest of the way up? I don't mind that but I want to be sure.

My mains is around 120VAC.


if you have a 110v transformer and its output on the secondary is 12v you will get the same results ...so back to back trany idea same still work .

As far as buying vs scavaging, when I was a kid If I needed anything I would grab a junk item and pull a cap, transformer or whatever. It's just right now I have so many hobbies that I can't just keep so much stuff around I could grab parts out of. I would be very embarrassed to show you or anyone the stuff I do have at it is.

Thanks,
Pete


A shed is my hide out for my junk just few boxes of scrapped circuit boards ,i always on the look out for stuff ...its a mess at the moment need to clean and neaten it for the warmer months when i do work out there . try not to hang on to things still cased as its just takes up to much space when all you want is the parts .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: XY Monitor / Display

Postby Steve Anderson » Tue Aug 28, 2018 12:16 pm

One thing I will add - if you are going the way of a voltage multiplier as shown above, buy new capacitors from the same batch (i.e. buy them all at the same time). If 'recovered' capacitors are used they'll probably have different leakage currents ending up with different voltages across them - possibly leading to an overvoltage on one or more of them. Who said "BANG!"?

Steve A.

From my local supplier a 10uF/450V capacitor is US$0.28 each, less if buying 10 or more.
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Re: XY Monitor / Display

Postby Steve Anderson » Tue Aug 28, 2018 5:38 pm

FlyMario wrote:I measured ohms between what I suspect is the heater and I get back 9.2ohms.

I find that a bit high, but it's possible. At least they're not open circuit.

Make sure you have the correct pins, the ones each side of the keyway, pins 1 & 11. Though all others should read open-circuit. For a CRT of this age you may need to clean the pins (all of them) to get a good reliable and low-resistance connection. Check your meter against a good known resistor of around the same value - replace the battery/batteries in the meter too. Touch the meter leads together, in a perfect world they should read 0.0 ohms, but usually a fraction of an ohm, 0.1-0.3 say. Make sure the 'Low Battery' warning doesn't come on as you do this (assuming it has one).

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Re: XY Monitor / Display

Postby Klaas Robers » Wed Aug 29, 2018 12:22 am

Pete, Fly Mario, to give you some overview in CRT's:
1. CRT's are in two variaties:
a. electro static deflection, with deflection plates inside the tube,
b. magnetic deflection, with deflection coils outside the tube, on the neck.
2. Type a. is always used in oscilloscopes, where you want to have a precise and high frequency (fast) deflection,
3. Type b. is mostly used in TV applications, where the deflections are sawtooth wise.
4. This is because it is difficult to have fast changes in the currents in coils.
5. the saw teeth for TV are relatively slow, and always the same frequency (speed).

6. A CRT needs a high voltage between the cathode (filament) and the screen,
7. the higher the voltage, the brighter the trace on the screen,
8. with the same very low current in the beam (generally 0.1 to 1 mA).

9. For (TV) picture tubes the cathode is generally at almost ground potential (0...100 V)
10. and the screen (anode) at a high positive voltage (5kV ... 30kV).
11. This is generally at a separate clip in the side of the picture tube, near the viewing screen.
12. These very high voltages cannot be transported via wires in the neck of the tube.

13. For oscilloscope tubes the final anode (screen) is generally at a voltage of about +600V
14. and the cathode (filament) at a negative voltage of about -1400 to -3000 V.
15. This still gives 2 kV to 3.5 kV over the tube, but for oscilloscopes you need less brightness of the spot.
16. The defelection plates should have a voltage slightly lower than the final anode (screen),
17. These voltages change according to the deflection of the spot that you like to have.
18. Voltages of 400 to 600 volts are just manageable with HV transistors or radio tubes.

The very high voltages are in principle dangerous, but if you design your HV power supplies such that the can only handle low currents (1 mA), you are relatively safe. The danger is in the current, not in the voltage. But any way, when you experiment with high voltages, higher than say 150 volt, only LOOK at your circuits when they are operating, and when really needed, do things with ONE HAND, keeping the other surely on your back. The bad habbit of working at a circuit while it is operating, should absolutely be abandoned. Don't be affraid, but think over before you do something.

In radio transmitters there are high voltages present (2 .... 10 kV) loaded with high currents (say 1A). They are absolutely lethal, but if you know what you are doing, you can have a long and a very pleasant life. Car driving, flying, swiming and diving can also be lethal,..... if you do the wrong things.
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Re: XY Monitor / Display

Postby Steve Anderson » Thu Aug 30, 2018 3:56 pm

Wise advice from Klaas. The 'one hand behind your back' (or in your pocket) is to reduce the chance of the current travelling across your chest from one hand to the other - the heart doesn't tend to like that! (A real understatement!). Don't be scared of electricity, but it demands respect - no negotiation. It's a wonderful slave, but a horrendous master!

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