Moderators: Dave Moll, Andrew Davie, Steve Anderson
Klaas Robers wrote:Looks good to start with Harry. Be sure to place and keep the transformer away from the picture tube, as the stray field will give a hum deflection on the trace. I made the same mistake years ago, however I had a mu-metal screen for the 3BP1 and hoped that would screen the magnetic fields. It did, but by far not enough.
There is no need to place the high voltage rectification and smoothing also outside the cabinet, this can be placed inside. It will require a multi wire connection to your picture tube unit.
In my Heathkit SB-500-cabinet for my SSTV monitor there was the ability to place the transformer at quite some distance. I will make a few photos soon and place them on this forum. Then you will see that I wound a shorted coil around the transformer to decrease the magnetic stray field. I don't know yet if it was sufficient.
Steve Anderson wrote:I wouldn't consider going down the road of using a 50Hz transformer in flyback mode, keep it simple, keep it linear. Two back-to-back transformers, say 12V-0V-12V will give you potentially +/-18V which can be regulated down to whatever voltages you need and also (perhaps with series resistors to supply the tube heaters, though unlikely the CRT heater itself). This stuff works, inefficient, maybe, but it does work. Efficiency is not a great concern to us. Reliability is.
Switched-mode and flyback supplies also generate a bucket-load of interference which can be difficult to eradicate. With 50Hz you know what you're dealing with.
Steve A.
Steve Anderson wrote:Harry, what sort of voltages are you aiming for? For a 3" CRT the 3BP1 is quite a high-voltage CRT.
If you don't have any data I attach two datasheets for the tube.
Steve A.
Steve Anderson wrote:I know this is of no use to you Harry, but a more modern and lower voltage CRT is the DG7-32. It can work as low as 500V but it is quite dim, at 800V it's far better. These are still to be found in Europe with sockets and are quite short in length compared to just-post-war CRTs like the 3BP1.
I'll have a detailed look at the 3BP1 data and see if I can make any recommendations as to how I would go about it. I assume you wish to use this for NBTV not SSTV. I'll also assume that apart from the CRT itself, you want to use all semiconductor parts.
Steve A.
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