[dreyfoos]

Gentlemen, I’ve met my match. I’m at a dead end. I need to use one of my lifelines.

On the bench: one Philco 50-T1403 (Code 125). This 12” beauty was won on eBay a couple of years ago and has just now found its way to my bench. It first arrived as a UPS total whack job. The top of the arch top cabinet was crunched in and the back cover forced down to guillotine the neck of the previously working CRT. That provoked me to swear a bit. But time passes and I’ve done the initial gluing and clamping to begin restoring the cabinet. The power switch and interlock socket obviously needed replacement and were done. With a 5AXP4 test tube in place and all the lytics and Black Beauties replaced with shiny new, I brought it up slowly. (BTW – there were a number of minor variations in this chassis and that kept me on my toes to trace every component and make sure that my schematics (both Sams and Rider) matched this chassis. At full voltage, a badly out of sync raster and weak sound greeted me. But I’ve seen much worse. So I dug in and replaced a bad mica to fix the sync. I touched up the sound to get decent but not booming sound. At some point I lost HV and traced it to a broken wire off the fly. A delicate soldering job fixed that. Ta da! - a very nice 5” picture. I was ready to try a big tube. I had a high mileage RCA 12LP4 – but it came on bright enough. Just one problem. Bad focus. Of course, the design of the 5AXP4 gave me perfect self-focus when it was in place.

So, I thought, what could be easier than fixing a focus problem? Weeks later, I’m still at it.

Let me backtrack a bit. When the set was listed on eBay, there were photos and one of them showed a sharply focused but badly out of sync raster on this set. The previous owner had done some cap replacement and I double-checked his work. By the way I’ve had other business dealings with him and have no reason to believe that the focus was anything but perfect before he turned it over to UPS.

This model uses a yoke and focus magnet assembly that is bolted together – so the separation is preset with the whole thing snuggling up to the bell of the CRT. Because of that, I don’t believe it’s a matter of fore and aft positioning or of having anything installed backwards. All voltages appear ballpark. Where 330VDC is called for I get 340-350 depending on the position of the focus control. For the 325, I get 320-340. For the 310, I get 320-335. For the 250 which supplies the tuner, I get 280-290. For the -4, I get -3.3 to -3.5. I have checked the focus control and the focus coil and they have correct resistance. I have replaced the resistor shunting the coil (R127 on Sams) because it was a little too high (and I had a new one handy).

Just to be sure about the CRT, I replaced it with a N.O.S. 12KP4, but still had the same bad focus – on a blank raster as well. Turning the focus control doesn’t change the focus although there is a slight size change which I attribute to its slight affect on the B+ voltage.

When I put a meter in one of the leads to the focus magnet it reads 52-165 ma. – depending on the focus control setting.

This Philco also uses a permanent magnet that surrounds the electromagnet. As I understand, that is supposed to do the heavy lifting and the electromagnet does the final adjustment. Could it be that the permanent magnet (non-adjustable) is tired – even though it didn’t appear to be tired before the UPS ordeal? How would one gauge the gauss of the permanent magnet? I have no number for what gauss strength it is supposed to be. If it were found to be weak, then how would one give it a boost – since I imagine a replacement would be hard to find? So that’s it. I’ve skimmed the comments on focus in every one of my many repair books from the era and other than mentioning that high heat or a hard knock could affect the PM, nothing else is mentioned. Could this be an aging problem that wasn’t anticipated those many years ago? But how would that fit with the apparently sudden loss of focus? Anybody got a clue?

Roger