6502.org

That is why I didn't bother to do that in the first place.


I think that it max 500V output, but it might be for the insulation as well, so I am not sure.
I will send an them an email.

A thought occurs.

If you don't mind having the screen at high potential and distorting when you touch it... You could have the cathode of the CRT near ground voltage.

If you hold the cathode at 100V positive of ground
The focus electrode (pin 5) will then need a variable supply of 250V - 450V positive of ground
The grid will then need a voltage in the range of 20V above ground (black) to 60V above ground (white) [These voltages are VERY aproximate and actual values will depend on the individual CRT]

The final anode will be at 1500V positive of ground, as will the deflection plates.

You will then need 4 high voltage capacitors to connect the deflection plates to the scanning circuits. Each deflection plate should be connected to the final anode via a resistor of 1M.

This will then not need any special transformer for the heater and the grid will be at a suitable voltage for DC coupling to the video amplifier.

It's not usual to run an oscilloscope tube this way because for oscilloscope work it is most convenient to have the deflection plates at ground potential. It will work ok, the only problem will be that the image will suffer deflections if you bring grounded objects near the screen.

I got a reply from the local transformer manufacturer. They test the transformers windings at 2500V, but if necessary they can add thicker insulation. So the transformer is covered. I could get one that would have 2x 6.3, 250-0-250 for powering the tubes, and then couple the 250 outputs with a cascading circuit to get 2KV.
But before I go ordering anything more planing is needed.
Ok, so deflection plates can be coupled with HV capacitors, but what about Luma(brilliance) how do I get it working properly and avoid that DC restoration issue?
And should the tube supply be 250V or 350V?

The transformer you describe would be suitable, with a diode multiplier to generate the 1500V for the CRT. Remember that one 6.3V winding will need to supply 3A or more for the valve heaters and the other will need to supply 1.5A for the CRT heater. 50-100 mA should be enough for the high voltage winding.

With the cathode at 100V as I suggested in my last post, you could dc-couple the grid to the image amplifier, avoiding the brightness changes with change of image. This would also avoid the need for any special insulation on the transformer.

Your deflection valves (tubes for non-british readers) need a supply of 250-350 volts. The exact voltage isn't too critical as long as it doesn't vary.

The CRT heater uses 300mA, so I don't need more for heating it.
The EF80 use 300mA as well, so 2A should be enough.
But how do I couple the luma if the brilliance input is somewhere in the middle of that resistor network?

It is usual for the brilliance control to adjust the bias point of the image amplifier, so varying the brilliance control shifts the operating point of the amplifier and thus the output voltage fed to the CRT grid. I'm trying to find some example circuits but there don't seem to be many out there.

But how do I connect the brilliance amplifier output to the brilliance input of the CRT if it is already connected somewhere in that resistor network?

You don't connect the grid to the resistor network. Instead it is supplied directly from the amplifier. I'm trying to find an example circuit bit it is proving difficult.