21zp4a crt sub

[kf4rca]

OK. Try this. After the set runs for 5 minutes, turn it off. Then put two fingers on either side of the coil on the flyback and see if it's hot.
What type of bar generator do you have?

[timmy]

Originally Posted by kf4rca

OK. Try this. After the set runs for 5 minutes, turn it off. Then put two fingers on either side of the coil on the flyback and see if it's hot.
What type of bar generator do you have?

Flyback does not get hot and I have an rca wb-64a

[timmy]

5pf and 10pf mica these are in the hv area so if i were to use ceramic then I assume it should be npo. These micas were not changed since I was not able to find this value with a voltage of 2500v. Ceramic seems like the best way to go. But the sams shows these caps as mmf so this could also mean ceramic I’m thinking. Besides npo what is z5f and z5u

[timmy]

If I go by the sams and set the hv to 10.2kv like it shows the screen pulls in on the left and right about a half inch on each side but I may not have enough to adjust the width to fill it in being the width control only goes alittle bit. And either way the focus should be better but it’s not and it’s said that these big electrostatic tubes have very little focus control. Sams says 305v for focus I go 305-344v and makes no difference. I should try it and rule out if the width will fill it in.

[bandersen]

Setting the HV higher will likely cause the image to shrink. It's harder to deflect a more energetic electron.

Now the flyback also drives the horizontal yoke winding so it's not quite so simple. Generally, the more energy you dump into the flyback, the more HV and more deflection so they track.

Really it depends on the design and component matching. There's usually a sweet spot when you get the lowest cathode current, most HV and full width. That's why there are so many adjustments - hor. drive, width and linearity all need to be set properly to get optimal results. That's a bit of a black art.

[timmy]

Originally Posted by bandersen

Setting the HV higher will likely cause the image to shrink. It's harder to deflect a more energetic electron.

Now the flyback also drives the horizontal yoke winding so it's not quite so simple. Generally, the more energy you dump into the flyback, the more HV and more deflection so they track.

Really it depends on the design and component matching. There's usually a sweet spot when you get the lowest cathode current, most HV and full width. That's why there are so many adjustments - hor. drive, width and linearity all need to be set properly to get optimal results. That's a bit of a black art.

Well as of now I guess it’s safe to say I got the best sweet spot the screen is stable focus is acceptable and it looks good. I did set the hv to 10.2kv but the width couldn’t open it up was to much. I went over so many times with the both vertical adjustments afc to stabilize the horizontal hold and adjusted the rings on the neck I don’t think it can get any better since these sets will never be perfect. And when I lowered the hv it pulled in on the left and right but if I raised the hv to 13 kv a white line begins to show in the center of the screen 12 -6 position.

[bandersen]

I think there's an old trick to increase width by putting a ceramic HV cap across the damper tube

[timmy]

Originally Posted by bandersen

I think there's an old trick to increase width by putting a ceramic HV cap across the damper tube

Hmm well I never heard of that but I think I got it as good as it will be so I think I’ll leave it alone and not add any problems 😂

[bandersen]

GC made a wafer with built-in cap you could install between the damper tube and socket. I'll post a photo when I dig mine up.

[timmy]

Originally Posted by bandersen

GC made a wafer with built-in cap you could install between the damper tube and socket. I'll post a photo when I dig mine up.

That would be interesting to see. At this point I just wanted to try and make sure all was right so lowering the hv to 10.2 kv down from 12 kv would be the only reason to widen the screen so now it’s at 12 kv with full screen and width and height and linearity are good. How much would that cap for the damper expand the width ?

[timmy]

How would you adjust a 7810 positive regulator to output 5 volts with an input of 9 volts I know a resistor is used but which terminal and how to determine the right resistor.

[kf4rca]

A 7812 will not regulate with an input of 9V. If you want 5v output I would use a 7805 regulator. They also make 7806 and 7808 and I think 7809 regulators along with 7815 and 7824 regulators. You can use an LM317 as a variable voltage regulator. You should be able to find some circuits on this here web.

[Electronic M]

+1 .
you can with a couple of resistors make a 78xx series regulator output a higher voltage than it's design voltage (the last 2 digits of it's part number) but you can not make it put out a lower voltage.... unless you burn it out into an open circuit, but few regard a 0V regulator as a desirable part.

[timmy]

Any way to remove potted epoxy from electronics ?