Moderators: Dave Moll, Andrew Davie, Steve Anderson
Steve Anderson wrote:OK, seems you're one step ahead of me! The only advantage you get from lower voltages on the CRT is increased sensitivity of the deflection, i.e. less drive is needed to the deflection plates, but the existing deflection amps should be able to provide that. The advantages are a brighter trace and better focus, both needed for NBTV.
The maximum from cathode to anode 2/grid 2 is 2200v for a 3BP1. Pin 2 (-ve) and pin 9 (+ve).
Steve A.
Steve Anderson wrote:It seems there's some non-linearity in the horizontal (as you have the tube orientated in the video), I would sort that out first before you burn the screen - it seems awfully bright to me. Whatever is causing that may sort out the other matters...
Have a look at the deflection waveforms on the pins of the CRT (AC coupled), they should be nice straight ramps. If not there's probably a problem in the power supply...having checked the input to the amps is correct first.
Steve Anderson wrote:Whenever I come across anything like this the first thing I suspect (or at least check) is the power supplies are clean (no ripple or very little of it) and at the expected voltages. If they're OK and the input signal is correct then it has to be something within that stage. Garbage in - garbage out.
Steve A.
Steve Anderson wrote:Ah! I think I may have it...are you using the ramp generators as shown in my posting of April 17? If so we'll need to make some minor changes. Also what deflection amps are you using? If you can post the drawing of the deflection amps you're using, that would help.
If you can check the outputs of the ramp generators are truly nice ramps, that would also help - disconnect them from the deflection amps first and keep the CRT heater off. Set VR201 & VR211 to half-way, the ramp outputs at TP2 & TP4 should be about 5V p-p centred around 0V, i.e +2.5V to -2.5V.
I'll attack this more in the morning - it's getting late here.
Steve A.
Steve Anderson wrote:If you can check the outputs of the ramp generators are truly nice ramps, that would also help - disconnect them from the deflection amps first and keep the CRT heater off. Set VR201 & VR211 to half-way, the ramp outputs at TP2 & TP4 should be about 5V p-p centred around 0V, i.e +2.5V to -2.5V.
Steve Anderson wrote:The first thing I notice is that 'spike' at (mostly) the beginning of the line waveform. Then in later photos I notice that you're not using a 'proper' scope probe and that particular scope has no BNC input connector which means you cannot set the probe compensation correctly - not even at all!
I know you have better scopes kicking around, have you got ''proper' probes for it/them? Using this arrangement will likely lead to all sorts of confusion not only here, but on later projects. I suggest putting this scope back on the shelf and getting the 'big guns' out - it really isn't up to the job.
Steve A.
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