View Full Version : 1.5 inch crt


timmy
06-20-2017, 07:30 PM
I have this crt its 1.5 inch from one of those Panasonic tvs so I'm wondering if it can be used with some mods of course in one of those oscilloscope clocks that use electrostatic tubes but this one is electromagnetic. I would have to create a power supply for the hv and 3 volts for the heater. But if I do that and put the cathode in place along with the deflection places all wired in what I would be left with is the vert and horiz so what I'm wondering is can I apply a small amount of voltage to the deflection plates and just play around with different voltages until I can get a clock face in the center. Since the signal is already there for the clock I'm just not sure if the vert and horiz has to be pulsed and is why I was thinking just magnetically move the signal that's there already. Since electromagnets vary in strength with voltage.

Username1
06-20-2017, 09:09 PM
This would be an interesting project. I use to work on Arcade games back in the 80's
Asteroids which was a vector game used a yoke and magnetic deflection. So it's
possible. I assume you have a proper yoke for this little tube...? I think on most
transistorized tv's the yoke is 4 wire, H and V windings are in series. Separate
windings of course. If you already have the clock, I would, if it were me, purchase an
IC chip audio amplifier, like a 386 or so, they use to be available at radio shack.
It was about 2 watts output, or something like that.... Connect up the input from the
clock H or V output, through the amp and ground the other side of the yoke winding.
You would have to build 2 amps.

On the Asteroids games whenever it was resting, both H and V would return to the
center of the screen, rest. If you have a zero out from the clock it would return to the center.
Ideally, you have a blanking signal to cut off the crt.

Assuming all this stuff runs fast enough, refreshing 60 + times a second so there is
no flicker, then you should have a nice display. Since most items won't change much
in position, like numbers, Analog display?, Then I imagine the display would be quite
stable. At the very least you will get an idea how it will look at a small investment.

Oops, 125mw output, Still looking at the specs, it's a small investment, maybe there
is a slightly more powerful amp of similar specs you can try...

lm386 == http://www.ti.com/lit/ds/symlink/lm386.pdf

2 watts circuit == http://www.eleccircuit.com/lm386-amplifier-stereo-2-watts/

Engineering help == https://electronics.stackexchange.com/questions/134131/how-to-improve-lm386-amplifier-circuit

I have a radio shack AM hand held radio with that IC amp in it, and the sound quality
is quite good, and clear. As long as the slew rate will work for the clock signal,
I would try it....

You might have to use something like a 741 higher slew rate, but then you have
to feed it both + and - supplies, and pay attention to where the zero is, and I'm
not sure about sink and source currents on that chip. 1439 ? you gotta look into
the spec sheets of different IC amps, cheap ones in case you toast a few......
I was thinking the audio amp because the cap coupling would protect it a bit....
and there are plenty of ready made circuits out there, ac coupling should be
fine cause in Asteroids you could hear the vector signal in the yoke.....
How you gunna get hv?? It can't come off the vector signal.... You have
to make a free running HV source.


Good Luck....

.

timmy
06-21-2017, 06:33 AM
I have the horiz and vert IC chips that were used for the tv the tube came from maybe they can be used or would be better to use, I don't know. It seems to me you have a better understanding on this subject already. And yes the tube has a yoke with 4 connections. The tube has 5 connections on it but the tube used for the clock has I think 10 connections so I'm not sure which ones would have to be used. I don't even know if this tube will work with the clock being it has adjustment pots that may not bring the image down to the size of this small tube, down from a 3rp1. The hv should be around 2.2.5 kv and a bug zapper circuit with the bleeder resistor used generates just that. The other possible problem is the cathode is shared with the heater on this small tube and the clock circuit has a separate cathode so that means a separate power supply for the heater. Then there is the sweep board from the tv the tube came from, which has pots, hv , heater voltage but there was problems with that board where the traces were corroded, a common problem with those tvs. If I can get that board working maybe I can use that.

Username1
06-21-2017, 07:21 AM
Heater and Cathode tied together, that's easy, heater must be DC, and you have to
be aware of what heater wire gets ground, and which gets the 3v. You will also have
to come up with focus circuit biasing and build a blanking circuit. Your clock board may have
an overkill on output wires.... Maybe there is a ground point for every axis? or a + -
for every axis, you have the schematic or pinout on this clock?


If the clock has adjustment pots, then probably for centering, and amplification for
each line. Remember scope tubes have 2 v plates, one up and one down, 2 h plates,
several focusing elements, and the usual heaters, g1, g2, etc.

.