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Originally Posted by rca2000
I acquired this old 7jp4 yesterday
... house after-hours, (for obvious reasons...)and started it up, without the rectifier tube. All filaments glowed including the 7jp4 in the set. SO...I just "touched" the 5y3 in its socket, while watching the screen--and I got SOME raster!! Plenty bright, but all distorted and compressed into a blur of an inch or two. This means that the tube in the set is pretty good.
Next-- I unplugged the set's tube, and plugged in the "new" one I got. VOILA!! I get a "partial" raster from this one, too. ALL compressed, jerky and bent, but PLENTY bright!! ALL of this took place in the kitchen, under the celing fan light. I had a more than bright enough raster to see in that light.
SO...does this mean that this CRT is good? Can a 7jp4 be "bad" even though on a set with problems it produced "some" raster? Will the tube still produce the same decent brightness in a set that is working right??
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Realize that when you restore the TV set chassis (recap and so on) and get the deflection to give you a normal sized picture, the "brightness" of the raster will be dimmer as the electrons will be spread over a larger area. IIRC, early TV set CRTs were dim compared to more modern ones anyway. That you'd have to draw the shades to watch the soap operas on a sunny day...
Both CRTs are probably good. And the fact that you did get a raster indicates that the flyback is highly likely good. And various other hard to locate parts likely are good too. Replace all the paper caps, and check high resistance resistors (above half a megohm tend to go bad to higher resistance) and the electroytics should be replaced too. I'd say that there's a good chance that a resoration should be successful.