Compensating CRT Deflection Coils
July 26, 2014 8:31 pm ProjectsThings look really weird when you use an uncompensated deflection coil with a vector graphics display. This is because the coil looks like an inductive load to the driver amplifier, and the parasitic capacitance makes it ring. Ringing and overshoot create the strange-looking display, basically extending every line past its destination.
One way to compensate for that is to add a series RC snubber in parallel with each deflection coil. You can perform some calculations to figure out the values of the resistor and capacitor but they won’t get you very close to the answer. There are just too many parasitics to model. It’s much faster just to build a RC substitution box and tweak the values until you get the result you want.
Richard :
Date: July 31, 2014 @ 9:44 am
Eric. Great job, fella! Does this apply to directly driving raster scan ramps, at non-standard rates, into the deflection coils? Please reply to me via email.
Richard :
Date: August 13, 2014 @ 10:17 am
Howzabout an update giving the construction details of your final deflection yoke?
eric :
Date: August 13, 2014 @ 6:11 pm
I’m still refining it. Same with the board design. Check back–eventually I’ll put it here!
Richard :
Date: September 17, 2014 @ 3:32 pm
Did you know that the high voltage connector on your CRT is known as a “J1-21”? This is the generic name for that connector. The cuter connector that resembles a clothing snap, like used on a 3JP1, is called the “J1-22”. I recently tried to purchase ten of them from a defense contractor, the “onlyest” source I could find. I was given a quote of $38 for twenty five of them. Not being too observant, it turned out to be $38 EACH! Or $950 for 25 connectors. No. Not going to happen. An alligator clip works too.
Richard :
Date: September 19, 2014 @ 12:46 pm
At what second anode voltage are you running your 5AXP4? I just got a sweet self contained 15KV power supply that is perfect for this tube. There is only one left. Write to me off line and I will tell you where. $148 shipped out the door.
eric :
Date: September 23, 2014 @ 3:31 pm
Yes, I looked into obtaining some connectors, and they’re hard to find. I have a couple of the metal clips, and I was able to 3D print (with a soft rubbery material) the insulating shell.
eric :
Date: September 23, 2014 @ 3:33 pm
The 5AXP4 worked fine at 5KV. I air-wired a capacitor multiplier to my HV board (the schematic has a diagram showing where to connect it).
Richard :
Date: September 25, 2014 @ 11:21 am
I got the 15KV power supply. It is huge and heavy. At least 25 pounds! I guess its a neon sign 60Hz transformer inside. A lot of iron in this baby! It’s also a lot larger than the CRT itself. Like this supply was made for a 14″ or larger tube.
Labguy :
Date: October 5, 2014 @ 8:15 pm
Fired up my 5AXP4 today. Check it out:
http://www.labguysworld.com/Project_5AXP4.htm
eric :
Date: October 8, 2014 @ 10:03 pm
Looks really good! I like the support blocks.