Philco 50-t1483 Focus problem
 

Hi all,
I fired up the philco after recapping and the i could not get the picture into focus. I found that the focus control had several dead spots so I replaced it but still cant get the picture to focus cleanly, any suggestions, thanks
Brandt

Does the focus control have any effect at all? You might check the focus coil for continuity (assuming this is a magnetic focus set).

Hi Brandt,

Some three years ago, I had a focus problem on one of my Philco 50T-1403's and sought help here from my fellow collectors. It became a fairly long thread which looked in depth at the parameters that govern focus - with emphasis on what Philco was using at the time. The name of the thread was "Philco 50-T1403 with focus problem."

http://www.videokarma.org/showthread...+focus+problem

Don Lindsly was expecially patient and generous with his help and we finally got my focus up to 100% - on the money.

Your Philco model may have the same combo of both permanent magnet ring and electromagnet coil that mine used. In any case, I hope that the old thread helps you move forward in solving your focus problem. I still have questions as to the effect of 60 years of heat and hard knocks that might affect the strength of the permanent magnet ring and hope to get back to it some day.

Good luck!

Roger

Tom,
the focus coil reads a couple ohms off but well within tolerances. The adjustment when its turned up will cause the screen to enlarge a bit but the focus does not get any better. After reading around here a bit I tried lowering the brightness to a minimum and set the contrast in a dark room and the picture is better but not great. Again the focus pot does shift it but it doesn't get any better. I saw from a few posts that if the CRT is gassey, this problem will occur but i guess my next question is that none of my crt testers show bad emission or shorts (beltron 8080 and a BK465), would they be able to detect the gassey condition?
When the brightness is turned up, the screen washes out and looks even worse, I have another 12lp4 and gonna try swapping it to see if this corrects some of this and if not will look into the focus system.

Thanks

Try a new 1B3 high voltage rectifier. If no better, check resistors under 1B3 and 500 uuf high voltage filter cap.

Does the brightness go completely out when turned to minimum? Is there enough width?

I think if the CRT were gassy enough to affect the focus that you would be able to see the blue glow of the beam. I have a test CRT that is gassy enough to see the beam, but it still has decent focus.

Did you look at Roger's thread? Checking to see if the focus coil leads are reversed sounds like a good idea.

How did the grid cutoff test of the 12LP4 fair with the BK465? If it's really low you might also be seeing the hollow cathode effect (I think that's what it's called) where the center of the cathode is dead and the emission is only from the edges, which wouldn't give you very good focus.

John

Do you have a magnetic focalizer unit handy? The kind that RCA and others used in 1952 and newer sets. If so, try it instead of the original. Also, if the set has the original Philco CRT it has a single magnet ion trap. If you use a different make CRT make sure you have a double magnet ion trap on hand.

The Philco 12LP4 required only a single field magnet? I've certainly seen many 12LP4s with a single field magnet but I could never figure out if these were replacement magnets or factory installed.

John

hi all,
tried several thing from all of your great suggestions and ended up finding out the focus coil was not working. Even through the coil ohmed out right, i couldn't get the focus to come in. I had a spare coil from another set and after exchanging it, this is the first picture i got up. Thanks for all you help as this is a great site
thanks again,
Brandt

Hi Brandt,

Glad to hear (and see) that you have those nice sharp scanning lines. Now I'm wondering what it is about the transplanted focus coil that did the job when the one that ohmed good didn't. There's always the matter of getting proper position of the coil behind the yoke and relative to the innards of the CRT. But what else could account for the fix? Was the substituted coil the same part number as the original or was it just a lucky grab? I wonder now whether almost any focus coil from a 12LP4 equipped set would do the job?

I'll bet someone here can clear this up

Roger