Moderators: Dave Moll, Andrew Davie, Steve Anderson
Steve Anderson wrote:Small change to ensure both counters start at the same time...hopefully eliminating that 'part-line' retrace...
A more elegant solution would be a Schmitt trigger and a cap, but this is quick, simple, and I can see you're out of board space!...and amazingly I was able to find the circuits!!!
Each time you change the line or frame rates (and power-up) I suggest giving the push-button a nudge...just to make sure...
...so, you see, I do make errors....
Steve A.
As usual, click image for higher resolution version, right click and "save image as'...
Steve Anderson wrote:Possibly one of those 6V switched-mode power supplies from e-bay and the like for one CRT with an appropriate dropper resistor (if required). Don't forget the heater needs more current at switch-on than when hot. Measure the heater cold resistance and calculate the start-up current required.
I'll think on this some more...but no promises...
Steve Anderson wrote:OK Harry. I think that this uses 3BP1 CRTs? Which may require a different span of focus voltages from whatever the original was, I don't remember. If so I'll re-calculate whatever changes are required.
Hmmm, the original was also a 3BP1...check all the resistance values around the CRT, especially any pots if they're "recycled".
Steve A.
Steve Anderson wrote:The voltage across the 5v1 zener (ZD101) should stay constant whatever the brightness/focus settings are - there's still something not quite correct in there!
Steve A.
Steve Anderson wrote:The voltage across the 5v1 zener (ZD101) should stay constant whatever the brightness/focus settings are - there's still something not quite correct in there!
Steve A.
I've just looked back at the original, I now realise that you're running this CRT at a somewhat lesser voltage than before (1400v), so your change is probably valid.
Steve Anderson wrote:The CRT will de-focus at at far lesser brightness than you're probably used to on the previous 3BP1 build - significantly. Just 10% drop in the voltage will lead to a significant loss of brightness and earlier defocusing.
I've checked the datasheets for the 3BP1, really -1500v is the minimum recommended for satisfactory operation. OK, we 'got away' with -1400v last time, but that was made up by A2/G2 being at about +180v, i.e. nearly 1600v across the tube. Here it's really a bit too low. This also upsets the voltage distribution across the resistive divider chains, including 'that' zener.
It's probably time to re-think the power supply - sorry.
Tubes are far more fussy about applied voltages compared to semiconductors - especially CRTs.
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