7jp4 tube is it bad?

[fumplet]

Hooked up my new 7vt5r tube to my known working ts-18 chassis and it worked for a while but did I just bump the vertical height knob or can these tubes short out and start to load down the vertical circuit causeing the height to shrink bottom to top. Image was centered top to bottom but shrunk. I switched it off and hooked up the original good tube to my good chassis and it showed normal raster. I do have the sencore cr 70 tester but as Ive read chassis hookup is best for tests?

[kvflyer]

A real working chassis is the best tester for a 7JP4. Often they can test great on a Sencore CR70 only to to find out that the tube is very dim because the phosphor is burned.

[fumplet]

well it did work so did I just bump the vertical height knob and all is well or can these tubes short and start shrinking the bottom and top of the raster so it has like just under 3 inches of raster bottom to top? Its not quite as bright as my Early Television Museum 7jp4 but its good. Dont think I will ever get a tube that good again. No raster on the 7vt5r chassis but experience from my first set tells me it needs a recap as I didnt get raster on the 1st chassis either until some caps were replaced.

[bandersen]

I've never encountered anything like you describe. I've seen plenty get dim with age, but no problems beyond that. I suspect there's a loose connection in the base. Possibly only one vertical deflection plate is getting a signal. Look for loose pins or cold solder joints at the ends of the pins.

[fumplet]

I dont know how long these 7jp4 electrostatic tubes last so Ive been afraid to watch my motorolas much at all. Cold solder joint might make sense, as tube heats up it looses connection.
What symptom should I be looking for if the tube is bad and it will damage my good chassis?

[fumplet]

threw it on my sencore cr70 tester and it does have a little cuttoff so I hit it with manual restore just a couple of brief taps, I didnt hold down the button. Now it has cutoff but needle jumps around. Im not sure if thats the tester or the tube.
https://youtu.be/UBU__jti0HI

[kvflyer]

I don't know this for a fact but many times on the Antique Radio Forum in the TV section, it has been said that electrostatic deflection CRTs (like the 7JP4) often do not respond well or at all to a rejuvenation. But what do you have to lose?

[fumplet]

Good to know on dont respond well to rejuvination. I didnt want to hold down the rejuv button like the testers instructions said to. Seems i get varying cutoff results when flipping through the emissions/filament set/cutoff/shorts/ after i set it back to cutoff
. I might try to resolder alll the pins. I tried pushing on the pins with my finger and i can affect cutoff when doing so. Cutoff goes way up when touching certain pins

[bandersen]

No, they do not rejuvenate well. The cathode is smaller than on a magnetically deflected CRT. I tried with a CR70 on a couple weak ones and it made them worse.

[kvflyer]

Originally Posted by bandersen

No, they do not rejuvenate well. The cathode is smaller than on a magnetically deflected CRT. I tried with a CR70 on a couple weak ones and it made them worse.

I have a couple that are weak. Sometime this weekend, I can try it and verify what happens.