Klaas Robers wrote:Harry, it depends on what you have for voltages available.
I have a dual 300 volt supply......but i find hooking it up to the focus and brigntness pots it drops this supply to 100 and 50 volts acoss those pots .
The I am pretty much using circuit as shown below but i changed the diodes from half wave to full wave rectifier on Steves advice for DC supply but i also have 2 load resistors still onit acoss the positive and negative supply ...i put them on to drop the voltage at touch to 300 volts and to bleed the voltage away when switching off power for safety ...may over kill now as i for got about the pots being in parallel with those Pot resistors .
I used modulation of the cathode and the control grid for brightness control.
Testing the control Grid today with a negative voltage -12 volts halfs the brightness of the raster line and i would guess say 50 would extinguish the beam .
It seems a touch less voltage hungry than this way ,i noticed when i was researching this on other sstv's most used your way cathode to modulate but i wasn't sure if i could use it on my tube as they were all your CRT type .
I had a voltage of +100 volts available and something as +300 volt for the first acceleration and focus control. What voltages have you now for the CRT? I think that - 300V is rather rare.
Yes as i mention above dual 300...it was easy as it uses the same transformer AC supply as the 3PB1 .
This is the video filter, don't mind it. And the video amplifier with kathode modulation. The BD115 is an old transistor that can have at least 100 volt. You see too the brightness control on the right, controlling the G1.
In the middle is a help circuit. In fact it creates an adjustable voltage with the BC107 emitter follower, giving a voltage equal to the input voltage of black (1.15 volts). See the video wave form below the circuit. This makes it possible that the contrast potentiometer is not affecting black, and only controls the shades grey and white. You can adjust that with the trimmer potentiometer ZB. If set at a wrong voltage, black varies also when you adjust the contrast control. You don't want that.
If you can't see the diagram completely, download the attached .gif file.
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Looking that your circuit it uses a dual 6 volt supply i have a dual 12 volt supply for the main circuits and + 5 volt for the inverter .
If you think your circuit with transistor changes will work on mine i am fine to give it a go and see it would mean just not using the negative 300 volt supply and dropping the positive 300 to 100 not hard to to doing it now without trying
(would it operate without a blanking signal just for testing ?)
I am sure i would have some thing handy for transistor substitutes.
i will have a look for the parts and get it together give it a go this week .
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.