Why or why not, would you use a CRT TV PSU, to run another CRT ? - Page 1
Forum section: electronics / repair

author: MathWizard
author_rank: Super Contributor
timestamp: January 20, 2023, 07:58:31 pm
content: I have an old vacuum tube CRT oscilloscope without a transformer, and I could probably get another cheap VT scope for the less than a custom transformer.But for the CRT, I have a working CRT TV PCB, with the HV flyback. I'll look up the model, it might be 10kV, but I only need about 800VDC, for a few resistors, and the scope CRT. So just with a resistor divider network, with the properly rated resistors, and any extra insulation needed..........is there any reason why the TV CRT flyback, would not work for the much lower voltage scope CRT (assuming any control circuits are happy, or the whole thing is just working anyways). I would remove everything from the TV PCB as I could. I would certainly want to keep the flyback on the PCB.

author: CaptDon
author_rank: Super Contributor
timestamp: January 20, 2023, 10:03:50 pm
content: You want to drop over 9KV with resistors? A dangerous waste. Where are you going to get the plate voltages and perhaps bias voltages for the vacuum tube scope? B.T.W., the CRT TV needs the yolk as part of the flyback H.V. circuit as they resonate together at something like the 5th harmonic of the sweep frequency to get the rapid retrace. Take away the cumbersome yolk and your high voltage goes away with it. Also, generally speaking the scope CRT cathode and filament operate at around -1200vdc and the filament usually has a dedicated highly insulated winding on either the main power transformer (old scopes) or the high voltage flyback on newer scopes with about 12KV on the post deflection accelerator.

author: shakalnokturn
author_rank: Super Contributor
timestamp: January 21, 2023, 03:31:16 am
content: For only 800V there must be far more appropriate devices to reuse:2 small transformers back to back followed by voltage multiplier.Insect zapper transformer.Laser printer "HV" transformers (not sure on current requirements or output polarity here).

author: MathWizard
author_rank: Super Contributor
timestamp: January 21, 2023, 10:18:55 am
content: Well IDK what the average TV voltage is, but ok so it's not just the flyback, the yoke is part of the circuit too.I think the CRT plate voltages are +or-200V, the vacuum tubes would need a +/-300VAC supply, plus their heater windings.Yeah I was just wondering since I the scope and the TV board unpacked at the same time. IDK where to get old transformers, that might be suitable. And I don't want to daisy chain them together, it would weigh a ton.This project can wait, I don't know near enough to mess with HV anyways.What I could do, is convert it to an LCD screen, but after I learn how to program such a thing. That would be cheaper.

author: inse
author_rank: Super Contributor
timestamp: January 21, 2023, 10:55:43 am
content: Which model do you exactly have, analog or digital?There are in principle four display combinations:Old style analog with cathode ray tubeDigital with CRTDigital with picture tube ( like b/w TV)Digital with LCDThe only chance to replace tube by flat screen is the picture tube variant.The classic CRT has electrostatic deflection while picture tubes have magnetic deflection.