Philco 50-T1403 with focus problem
 

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

Roger:

Did you try my suggestion that I posted on the Antique Radio Forum? You never know, it might fix your problem.

Steve

Steve, my Philco does not have a DC restorer tube – at least not labeled as such. I did substitute for the 6V6 video output and the 12AU7 video det. – agc rect. – video amp with no change in the focus situation. As you said, worth a try. I’m wondering if your Stromberg Carlson really had the same problem? That is, did it have sharp lines on the blank raster or was the focus bad only with a picture? My focus is totally pooped out all the time and that leads me to question the P.M. encasing the focus coil – simply because I don’t know how to test it and I have no readily available substitute.

Roger

Roger:

My Stromberg had very poor focus without a signal. I could not see the scanning lines. The focus control changed the image but never brought it into sharp focus. I finally turned my attention to the video output and found the bad DC restorer.

Steve

Steve, I forgot to remind myself and all that I get an excellent picture on the 5AXP4 test tube. Wouldn't that take the video section off the table?

Roger

Roger:

Yes, you are probably correct. Darn, it would have been an easy fix otherwise! Perhaps your focus coil has some shorted windings? It could still measure correct for resistance.

Steve

I have a 12" RCA (2T51?) with this problem. It just uses a permanent magnet for focus. First I found that the travel of the magnet is very limited-after a lube job and with some help I can get it to go through the full travel. From looking at other sets this looks like a common problem. But, even after getting that figured out the focus still won't improve. I tried swapping magnet assemblies from another set (I do have some spares) but still no luck; just holding a strong magnet up to the neck didn't seem to change the focus either. I had guessed, in my case, that I had either B+ problems or a defect in the crt. I am going to follow this thread close. I will have to look for a possible DC restoration issue, I guess; without reading the ARF thread, wouuld it effect this set which only uses the perm. magnet?

Strange that the test tube would work. It seems like that would eliminate everything but the crt but it doesn't...

Hello Bryan,

You mentioned the test tube situation. In my case, I used a 5AXP4 with an electrically identical yoke from a similar Philco set (but not a similar magnet). In that lash-up I also used a resistor in the connecting harness to sub for the focus coil which I didn't need since the 5AXP4 is self-focusing. Of course, a gassy CRT can also cause bad focus. My understanding was (before Steve's comment above) that if you can get sharp scanning lines on a blank raster then the appearance of bad focus eminates from a video problem. Now, perhaps a video problem does have to be considered. Somehow, I still think that my probem has to be in the magnet area. It would be nice if we could make a definitive measurment but I don't have a magnetometer in my toolbox and I dont have a factory fresh strength number anyway.

I may yet try to rig up the permanent magnet or even the electromagnet from the other set. I'd like to avoid all that if possible as the circuitry is a bit different.

Next step might be to sub a third 12"er just to make sure in that area.

Roger

Have you measured the high voltage?
Have you reversed the focus coil leads?

Don

I have heard that magnets can lose their strength when dropped quickly. But even as hard as this set was treated in shipping it seems unlikely it would be enough to kill the magnet.

I couldn't get a good scanline on mine no matter what. Complicating the issue is that my set is designed for an electromagnetic speaker, which is missing, so I have experimented with various combinations of power resistors or other speakers to compensate. I have had the B+ too high and too low and the picture never focused. I need to find an original speaker or a proper choke, I suppose. A back-burner project.

That's the ticket, Don. I owe you. I reversed the focus coil leads. Huge difference – went from 0 to maybe 90% perfect.

However, the best focus then appeared to be just out of range of the focus pot at maximum CW rotation (with blank raster or video) So then, I switched from the 12KP4 (which I bought as N.O.S. from Surplus Sales of Nebraska some years ago) to the (old RCA) 10BP4 and the focus went up to 99% - but still at CW max rotation - perfection just out of reach? Any thoughts? I had previously replaced the Rider C65 (Sams R127) 100 ohm, 1W focus coil shunt. The focus pot checked fine at 500 ohms.

BTW, the HV is 8900 VDC. Koinkidentally, I had been ruminating about those focus coil leads. IIRC, I had some reason to re-solder them a year or two ago. I had red to red and green to brown. That green to brown was a clue. Now it seems very logical that there is a polarity dimension that I had not accounted for.

Roger

Bryan, I found a thread in the AK archives that might give you some ideas. About half way down this thread you will find a discussion of permanent magnets that perhaps weren’t so permanent and needed to be “goosed.”

http://www.audiokarma.org/forums/arc...p/t-37424.html

Roger

The high voltage looks fine.
Does the focus coil now need more or less current for a perfect picture?

Don, more CW rotation gives more current - higher current yields best focus.

Roger

Roger, thanks for looking that up. I vaguely remembered that thread but had never gone searching for it. I've printed it and will stick it with set.

Roger:

The focus pot and a 150 ohm resisitor are across the focus coil. To route more current through the focus coil, make sure the voltages on the 6V6 audio output are correct. Check the 5K B+ stacking shunt and grid divider resistors.

Since the high voltage, width and vertical are OK, we can assume they are drawing the proper current, or close enough for focus.

The focus control circuitry is across the focus coil so routing more current through the focus coil requires raising the value of the shunt resistors. If the 6V6 voltages are OK, then raise the 150 ohm resistor on the focus control to about 330-500 ohms, 5 watt.

Don

...

[QUOTE=dreyfoos;1697038] "I reversed the focus coil leads. Huge difference – went from 0 to maybe 90% perfect."

Just to confirm, I looked at my 50-T1403 and the focus unit wires [PM with a coil] are connected green to red and red to brown.

Try to find a copy of the 1950 Philco Yearbook which contains full information for all the 50-T sets. There are several pages of factory updates which will greatly improve the performance and reliability of these sets.

Here's where I am. First to the Kolordapter Kid (cbenham): Yours works - mine didn't. I put a Color-dapter together some fifty years ago but never got it to work. I don't know if I would do any better today. If I still had it, I would sure give it another try.

Yes those focus coil wire connections do make the difference between no affect by the focus control and, for me, an "almost there" situation.

Don, my version (50T1403 code 125) uses the 6AQ5 for audio output and the only voltage that seems significantly off is the 132VDC on the grid where Sams calls for -38VDC. Remember, my audio does seem a little anemic. Could this be an error in Sams or, perhaps more likely, this is a problem to track down. I've got a lot to learn (or remember) before I get this straightened out. Now I have found a couple of B+ resistors that were 40-50% high and have replaced them and am looking for more. There might be some slight improvement in the focus range as I can now see lines on the 12KB4 where I couldn't previously. The range is still not right though, as best focus is still with it cranked all the way clockwise for maximum current. Still wondering whether the PM is carrying its share of the focusing task.

I subbed a higher 300-500 ohm resistance for that 100 ohm shunt and noticed no change except that at 500 ohms - no raster.

In some of the old Philco production run changes quoted in Riders I found an earlier model with this "R66 changed from 180 to 100 to center range of focus control. So, that's where I'm at.

Maybe I just need new glasses.

Roger

Whoops. That should be a -3.8 VDC from the Sams.

Roger

I will look up another print.

Don

Update: I just subbed a focus assembly from a slightly earlier 10" Philco model - with no improvement - best focus setting still max CW. I had restored that chassis and then put it on the shelf. I recall no focus problem when I was working on that one. I only remember an excellent picture. It's not convenient to fire it up right now but I did check the position of the focus control and it was very low - not quite fully CCW.

Roger

I found another print showing the 6AQ5 audio. What are the grid, plate and cathode voltages? Earlier posts state the B+ voltages are slightly high. That may be due to slightly higher line voltages.

Is the 5K stacking resistor OK? When you remove the 6AQ5, the sound and picture should go out and the screen should go blank. If not, something is bleeding through to the 135 volt source.

There is too little current through the focus coil, (no kidding). Do you detect any circuit revisions? Is something left out? You posted the current through the coil. What is the total current drain?

What is the exact focus coil resistance when measured with an analog VOM? Digital meters will give false readings on high inductances.

...

Okay Don, I've got fresh numbers for voltages on the 6AQ5 audio output - all with a VTVM. Sam's calls for -3.8 VDC on the control grid, pin 1/7, and I get 135 whether to ground or to the cathode, pin 2. For the screen grid Sam's calls for 165VDC measured to pin 2 and I measure 150 (Rider's calls for 290 to ground and I get 285). Sam's calls for 145 on the plate to cathode and I get 140 (Rider's 280 to ground and I get 275).

Specified line voltage is 117 and that's what I measure.

B+ voltages measured against Sams are 330/330, 325/312 and 310/270 - with the focus control at mid position.

The focus coil should be 170 and I read 180 ohms on the original and 184 on the "sub" from another Philco. That sub had just a hair better focus - very subjective (and still full CW).

The focus pot ranges from 0 to 500 ohms - on the money.

You asked about the stacking resistor. I presume that would be the Sam's R78 sand type listed as a "decoupling-wirewound." I subbed a new 5K sand and there was no change in focus.

As to measuring the total current drain - I don't have an ammeter that will handle AC. Perhaps I could measure somewhere after rectification?

I mention again - since we're "focusing" on the audio amp - that my audio is just barely enough - with the volume control fully advanced there is no "extra" volume available.

Also, I notice that according to my tube manual, the 6V6 does not use pin 6. Yet, Rider's shows the pin 6 connected to the 135V supply. Sam's shows two possible arrangements - one connects pin 6 to the 6AQ6 cathode and the other connects pin 6 through a resistor to the 310V supply. My 6V6 socket has a pin 6 that's clean as a whistle - looks like it's never been used. Could there have been a later factory mod?

When I pulled the 6AQ5 it killed the sound but a somewhat "faded" pix remained.

Roger

Roger:

The Sams is wrong on the control grid voltage. You are right. It should be about 4-5 volts less than the cathode and about 135 volts. I am using the Philco yearbook.

Sorry I wasn't clear on total current drain. I meant the total DC B+ drain at the 5U4 output, pin 8 where it feeds the filter choke and caps.

I like Andy's suggestion to set the focus pot to minimum resistance and drive the focus coil with an external power supply. Then measure the current and voltage it takes for proper focus. The 180 ohms is high, but not too high. It is within 3%.

The audio can be affected from a few things. That TV is no boom box. It has a small speaker in front. Remember people sat lots closer to a 12" TV than a 25" so high volume was not necessary. It should be about like a 5 tube radio. Make sure the 2 electrolytics are OK and the .0068 across the transformer is not leaky. There should be about 2 volts audio at the volume control high side and 6-8 driving the 6AQ5 at high volume setting. Check the audio output transformer resistance, particularly the secondary. Some develop high resistance joints internally at the connecting leads. It should be around an ohm or less.

Also check the 2uf electrolytic in the FM sound detector. When that cap opens, it will cause a serious buzz in an intercarrier TV, but that has split sound so it will only cause weak audio.

Don

Goal: Still trying to get the best focus moved to the center of the focus control range rather than just beyond fully CW. (Audio volume is marginally adequate.)

Correction: In my last post I thought there was something out of place on the 6V6 Vid Output pin 6 situation. Never mind. As some of you well know, Philco made it pretty “narrow and deep” in that area of the chassis and I somehow got disoriented on the tube sockets. All wiring is according to both Rider’s and Sam’s schematics.

Update: Going back to what Don said: “When you remove the 6AQ5 (audio output), the sound and picture should go out and the screen should go blank. If not, something is bleeding through to the 135 volt source.” I repeated that trick and I would describe the raster and video that remain as degraded but watchable – perhaps half the contrast as with the tube in. So where would I start to track down that possible short or low resistance? BTW, the 6AQ5 tests fine on my RCA WT-10A, but I don’t have any spares so I’ve ordered some new ones.

As to using another power source to run a higher current through the focus coil... I’m going slowly on this to make sure that I know what I’m doing. I don’t want to have to go shopping to replace an open coil. To make sure that I don’t burn out the coil, should I use a sort of dim bulb setup? (Not talking about me!) I previously measured 52-165 mA through the coil connected to the set’s B+ of 330VDC. So, do we not care what the voltage is so long as we keep the mA current, say, within 200 mA? What source would you use? Would a 13.8VDC source be okay and what would be best to limit the current? Would a 69 ohm resistor plus a pot be enough?

When I put the digital mA meter between the 5U4 output, pin 8 and the filter choke and caps, I read 0.11 A.

As to the audio: the electrolytics are new as is the .0068 and the output xmfr checks okay. The 2uf in the detector is new. I find 6V driving the 6AQ5 - but only about 1V on the volume control.

I continue to try to get schooled up on all fronts – including what it would take to make sure the permanent magnet is “saturated.” Just reading the Rider’s TV volumes 5 and 6 covering all brands is giving me a better feel for this. It's “Heavy” reading. Sorry, couldn’t resist.

Roger

Roger:

You're doing fine.

It is possible that enough current passes through the 5K stacking shunt to power the signal circuits. I would start by removing the 6AQ5 and one end of the 5K. If the picture and sound dissappear, then let's get away from there for a while.

At 110 ma, it seems the TV is not drawing enough current. That is in conflict with the earlier measurement of 52-180 ma through the coil. We're missing something.

Disconnect the focus coil from the TV and put a 150-200 ohm, 5-10 watt, resistor in its place to protect the focus pot.

Apply somewhere around 30-40 volts DC to the focus coil. At 180 ohms, you don't need any protection if you keep the voltage low. Two hundred ma works out to 36 volts. Adjust voltage for best focus and note the current. I suspect it will be somewhat more than 180 ma. If so, we can go from there.

I thought we eliminated the focus coil earlier by substitution. Did we?

Don

Don

Picture and sound do disappear with the 5K and 6AQ5 out and one end of the 5K lifted.

We did eliminate the focus coil as the culprit with a sub. There is still a remote but possible problem with the PM. It could have lost some of its pull (or push) and that would make the coil have to take up the slack.

With the focus pot protected I connected the focus coil to the 25VDC bias supply on my old B&K 415 Sweep-Marker generator. I could run the voltage up from zero to 27 and get about the same result as from the Philco B+, which is from fuzzy to almost sharp before I run out of range and the current is 147mA. The B&K also has a 50VDC bias supply measuring a smooth run-up from 0 to 50. With it connected to the coil I don’t get any focus – even at halfway – about 25VDC – nor at 30-40VDC. For some reason that 50VDC supply wimps out.

So I decided to lash something up to my variac. Got a RS bridge rectifier and tacked on a 10 MFD 450V for “smoothing.” I was reading a higher voltage than my input so I decided I had better find a formula for the cap value needed. I did – and it said I needed .01MFD. That didn’t work any better so I figured it needed some resistance across the output. That made the output read right and I dialed in about 30VDC.

So then I hooked the lash up to the focus coil. At 160 mA and 33VDC I got PERFECT focus - in alternating horizontal bands of the pix. Looks like way too much AC ripple in my lash-up. I really did take “electricity” in H.S.

Now it was time to reconnect the old chassis supply to the focus coil. Fully clockwise I get 160mA @ 28V, max current. Focus not perfect – kind of like when we take our reading glasses off. By the way, with the focus pot at the halfway point the voltage reads 19VDC.

I sure hope this is making sense to you. Any idea why I’m getting the ripple? Does it need something on the order of a 10, 20, 30MFD across that output and then take new readings?

I have no idea why the current was 147mA with the chassis hook up earlier this afternoon.

I haven’t worked on that “no make sense” lower current on the 5U4 than on the focus coil. Hope it doesn’t have anything to do with the meter I’m using – a $3 item from Harbor Freight. Thought I’d give you the other stuff to chew on first and take a fresh look at the discrepancy with the current tomorrow.

Roger

Very ingenious. You have eliminated the CRT and some other stuff.

Don't expect 180 ma from a bias supply. It may deliver 5-25 ma, surely not 200.

The bands are coming from AC ripple in your power source. It could use a low resistance choke and second electrolytic. A single pole filter won't do it for high current drain. Try a 5-10 henry and a couple of 10-30 uf caps. Anything that looks like it will work probably will.

Digital meters can be fooled by high AC ripple riding on the DC. That is why some measurements don't make sense. A Simpson 260 or Triplett 630 will give readings that more closely match the schematics on older TVs. They were the standard at the time.

I am still puzzled as to why there is not enough current going through the focus coil. Try a 10-20 uf electrolytic on the 5U4 side of the B+ source when measuring total TV current drain. That way both sides of the meter see (relatively) clean DC. Recheck electrolytic cap wiring, if any were replaced. Some high current circuit on the wrong side of the focus coil will cause poor focus.

Don

I don’t have a Simpson or a Triplett now but I do have a very contemporary old Hickok 203 volt-ohm-capacity-milliameter. Hadn’t gotten around to recapping it. I put the meter in the focus coil circuit and it jumped up but there was an obvious hitch in its get-along.

Maybe this meter maintenance issue deserves a new topic…a cursory web search didn’t find anything. I think that I need to get up to speed on cleaning and lubing that very delicate meter movement.

In the old days I suppose it would have been carbon tet and sewing machine oil – two things that aren’t likely to be found around the house these days.

BTW Don, I will triple check the wiring around the new electrolytics – some had been installed by the previous owner before I dived in and recapped the rest. Of course, I never make a mistake myself.

And, I’ll play around with that unwanted ripple in the alternate supply.

Roger

Avoid lubricants on the meter movement. Clean with ether or carbon tet in a sterile work area. Look for small stuff stuck between the movement coil and magnet. Fixing meter movements is a craft all its own. Some other members may have something to offer.

Progress? report:

First, a puzzling observation: the 100 ohm focus coil shunt (Sam’s R127, Rider’s R65) seems, at this time, to be superfluous. No difference in the raster focus whether it’s in or out of the circuit. I subbed all the way down to 0 ohms and up to several hundred with no effect on focus. I know manufacturers aren’t in the habit of spending extra pennies for nothing. Seems significant to me – could this be the missing piece of the puzzle?

It was noticed as I was inch-worming my way through the circuitry to verify every connection and component. I have found nothing out of place so far. All electrolytics are fresh and polarity double-checked.

I also rigged up for smoother DC from my breadboard supply to the focus coil. I used two 22uF 350V’s with the secondary of a filament xmfr in between as the inductor. There’s still a ripple but it’s much reduced – appears as one or two bands instead of six or eight.

It took 30 VDC indicated on my Variac and confirmed with the VTVM to get perfecto focus using the lower ripple breadboard supply. The current measured 195mA with the digital ammeter. This same alternate supply - without the new filtering - gave perfect focus at 160mA and 33VDC.

(I’m still trying to get an ammeter to confirm what I’m now getting with the digital. I took out the meter on my old Hickok and it seemed to be moving freely once I could hold it in my hand and subject it to gravity from different directions. Now I need to check all the shunt resistors in the range circuits and then there are the contacts and connections to clean up before I put it back together.)

Don, you said, "Try a 10-20 uf electrolytic on the 5U4 side of the B+ source when measuring total TV current drain.” I’m not clear on where I should put that cap relative to the meter. Do you mean in series with the digital meter lead?

Roger

Roger:

I would just put it from pin 8 to ground to clean up both sides of the power supply. You could also just put the ampmeter is series the choke on either side. It all amounts to the same thing.

If the 100 ohm resistor does not do anything, then it is probably because the focus control is at one end where it routes the most current through the coil.

First try a 150-200 ohm, 5 watt in series with the end of the focus control that is connected to the filter choke. That should center the control action.

Don

And now, ta-da, sweet success, I’ve got excellent focus (see photo). It’s been a long road and along the way I’ve received outstanding guidance and suggestions from those of you who for whatever reason are travelling this same road. Special thanks to Don Lindsly out in Colorado.

To catch y'all up: I had let this thread slide for a month as I took a different tack to get at this focus problem. For most of you, what follows will be old hat. But there may be a youngster or novice reading this…I’m no youngster but not much more than a novice either.

Strategies for solving a defect in a TV that’s way past old enough to vote depends on several approaches. If you have the knowledge of an engineer or “reverse engineer” you may know how to zero in on a few likely components as the culprit(s). Years of hands-on experience in the trenches and on the benches also goes a long way. Knowing what to measure and how can get you off to a fast start – if you have a good suite of reliable instruments. What makes the senior, or retired, or aged TV receiver so “interesting” is that it’s no longer anywhere near “factory-fresh” – boasting virtually all new parts with only one failure point for us to detect. That’s why those of us afflicted with old TV’s usually do a wholesale replacement of the statistically likely failure points – like all paper caps and electrolytics – and of course, a tube check. (BTW, I’m in the camp that feels no shame with having lots of shiny new Asian electros or orange drops showing. How do you re-stuff a bumblebee anyway? …but I’m sure someone has done it.)

Where it gets interesting, is when the part is not easily tested nor readily available as a new part. In this case, I did have a permanent magnet part of the focus assemble but with no way to make a definitive measurement (it would still hold a paperclip). I also had no new part to “sub” that final piece of the puzzle. I say “final” piece in the style of old Sherlock, who deduced from “the dog that didn’t bark.” In this case it was the permanent magnet part of a combination PM/ electro-magnet combination to handle the focusing. My books (from the era) told me that the PM does the heavy lifting in that PM/EM combo. I wanted to eliminate that PM as the point of failure. But I had no duplicate part with which to sub. Then, just in the nick of time, a twin of my Philco 50T1403, code 125 popped up on eBay. I decided to go for it – first, because I just like this model. But also, it would have the correct PM that I could use for a sub and eliminate that as the problem in the set which was taking up too much time and space on my bench. Of course, there was also the possibility that I would just end up with twin sets having the same tough-dog focus problem. Bottom line: got the twin, the sub worked and the focus is perfect – somewhere in the middle of the focus pot’s range. But is the case closed? No. I only have one good PM and two Philcos that need it. Anyone have a spare focus PM? The one that is around the outside of the EM (EM Philco part number 76-2622-3 or Merit number MF-1). I assume that there is no separate part number for the PM.

What causes a PM failure anyway? Temperature is mentioned. A hard knock is mentioned. Anything else that might be associated with age? Where would one take that magnet to get it refilled with the magic? Somewhere, I saw the word “saturation” referring to magnets. Does that mean the somewhat “unsaturated” magnet should be put in an appropriate magnetic field until it’s “full”? And where would I find a magnetism station where I can “fill ‘er up”?

One other factoid that bothers me: the PM with the problem has four scribe marks at the point where the EM wires exit the assembly (see photos). It made me wonder whether there is an orientation problem with the first set’s two magnets. Is alignment between the two critical? A month ago, I tested that by changing the alignment and noticed no difference but those scribe marks still bother me. The magnet assembly from the second Philco does not have any scribe marks. Someone, probably after it left the factory, made those scribe marks. Did they know it was critical to get that back to the factory position? But why are there four marks? Should I start rotating the old PM, one degree at a time? I really need some enlightenment (wild and crazy ideas) from the forums before I try to delve further.

Well, thanks for your interest. I’ve learned from this – hope you have – and that we’ll learn more.

(P.S., you can view the test pattern photo without the artifacts if you hover over the "zoom" icon in the lower right hand corner of the pix and click.)

Roger

I have now delved further.

Disassembling the yoke-focus coil stack on my #1 version of this Philco revealed an extra layer of nuts between the yoke and the magnets - based on what I found in the #2 set. That changed the presumably critical spacing between the yoke and the focus coil bolted on behind it. That extra nut shifted the focus coil's position over the gun by about 3/16 inch aft. Now, having "corrected" that, to duplicate the spacing found in my #2 set and having assembled the magnets from #1 with the yoke from #2, I find that the focus from the original situation appears to have changed slightly – now it’s 100% perfect at the extreme CW end of its focus control rotation. But it should be around the mid-point of the control rotation, as with magnet #2, and that still leads me to think that the permanent magnet from #1 is not up to snuff. So, on the one hand, I've got sharp scanning lines! On the other hand, no headroom in the focus control.

There are some contradictions to clear up. I will delve yet further.

Roger