Philco Model 41-296X with 41-285 modified chassis - Printable Version

+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Philco Radio Discussions (https://philcoradio.com/phorum/forumdisplay.php?fid=5)
+--- Forum: Philco Electronic Restoration (https://philcoradio.com/phorum/forumdisplay.php?fid=8)
+--- Thread: Philco Model 41-296X with 41-285 modified chassis (/showthread.php?tid=2069)

---

Re: Philco Model 41-296X with 41-285 modified chassis - Ron Ramirez - 12-01-2009

Don't give up yet!

Your resistance readings seem to indicate the old power transformer might still have some hope. The imbalance in the high voltage winding may indicate a potential issue, however...but those two resistance readings on either side of the center tap will never be equal, anyway, due to the way these transformers were wound. One half of a center-tapped winding will always have a somewhat lower resistance than the other half.

Here's a quick and dirty (and very easy) test you can perform.

Remove the rectifier tube from the radio. Unplug the speaker connector from the speaker.

Plug the radio in and turn it on.

If it goes POOF, forget about it...you need a new power transformer. But it probably won't go POOF.

Assuming it does not make any strange noises nor begin to emanate smoke, leave it on for a few minutes. Do nothing else. Do not assume all is well and put the rectifier back in.

Now turn it off, unplug it (important), and once you have unplugged it, see if the power transformer is hot by (carefully) placing your hand upon it. Do this very carefully...be prepared in case it is hot!

If it is hot:

The power transformer is probably toast.

If it is cool:

It may have some life in it yet.

Now go and doublecheck that field coil resistance. Measure it while the speaker connector is still disconnected. Remember, the field coil is the large coil in the back of the speaker, and should read in the neighborhood of 1100 ohms. (There are four pins on that speaker connector. You should read around 1100 ohms between the two inner pins, and only a few ohms across the two outer pins. That is the voice coil winding.) The small transformer under the chassis that is somewhat close to the power transformer is the audio output transformer, so make sure you are measuring the right thing.

---

Re: Philco Model 41-296X with 41-285 modified chassis - jjbuzard - 12-01-2009

On ther schematic there are two obvious coils, the one right next to the speaker (in the schematic) and the one next to the transformer (in the schematic) that says Field Coil, what is the coil physically next to the Main Transformer, (bottom side)?

It looks easier to replace the main transformer than I thought, colors are still obvious on this chassis.

---

Re: Philco Model 41-296X with 41-285 modified chassis - Ron Ramirez - 12-01-2009

jjbuzard Wrote:what is the coil physically next to the Main Transformer, (bottom side)?

As I mentioned, that is the audio output transformer under the chassis. Smallish, mounted with two rivets. It will have three thick cloth-covered wires coming from it, another smaller wire, and a wire that you may not notice that is soldered to the frame. The smaller wire and the wire soldered to the frame are the leads for the secondary winding of the output transformer. The three thicker wires are the primary leads - one is a center tap.

Take a resistance measurement (with the set off and unplugged) between the plates of the 41 output tubes. If you do not have continuity, that transformer is bad (which is very common). This will not affect your set's power supply, but if bad, the radio will not play.

---

Re: Philco Model 41-296X with 41-285 modified chassis - jjbuzard - 12-01-2009

I'm sorry, I don't know what you mean by Take a resistance measurement (with the set off and unplugged) between the plates of the 41 output tubes, what are the plates? and what should the resistance be if working? I noticed little berrys formed on the outside of the cloth covered wires coming from this coil, not alot but some.

Plus before I test the main transformer as you described above, I assume first I should replace the capacitor that I fried when all this started, before trying to test the main transformer :
Thanks for helping this novice

---

Re: Philco Model 41-296X with 41-285 modified chassis - Ron Ramirez - 12-02-2009

Hmmm...okay.

Do you have the schematic for this radio?

Locate part (58). This is the audio output transformer. See where the black wire and the white wire goes? Each of those wires go to the plate of a 41 tube. The schematic also gives the resistance measurements: 170 ohms and 190 ohms. 170 between one half of the winding and the center tap lead (black with white tracer), 190 between the other half and the center tap.

So if you measure between the two plates of the 41 tubes - in other words, between the black lead and the white lead - you should get in the neighborhood of 360 ohms.

Note there is no measurement given on the schematic of the right side of the winding - this is the secondary. You should measure only a few ohms on this winding.

Yes, those three wires do have little "bumps" or "berries" on them. All audio output transformer primary leads get that way in these 1939-42 Philcos. I don't know why.

Some time spent in learning the symbols of a schematic diagram will be a big help here. This link does not include symbols for tubes, but will get you started:
http://www.wisc-online.com/objects/index_tj.asp?objID=DCE1902

And here's another page, with tube symbols:
http://library.thinkquest.org/10784/circuit_symbols.html
It's like learning to read a road map. A schematic diagram is sort of a road map of your radio; it shows how everything is connected.

Edit: Oh, yes, please DO replace that fried 160 volt cap with a new 450 volt cap!

---

Re: Philco Model 41-296X with 41-285 modified chassis - jjbuzard - 12-02-2009

OK the resistance between the white and Black & white is 160, between the Black and Black & White is 460, between the black and white is 600, using the testor I get 60 using the X10 scale = 600 OHMs. So is this coil or transformer screwed up, should I just plan to replace this Field Coil and the main Transformer? Or does this indicate another problem :

Thanks for the web sites I will use them
Thanks again for all your help.
Jim

---

Re: Philco Model 41-296X with 41-285 modified chassis - Ron Ramirez - 12-02-2009

Jim,

Your test of the audio output transformer indicates that it is on the verge of failure. 160 ohms on one half and 460 ohms on the other is too much of an imbalance; it shows that the half showing 460 ohms is already failing.

You can count on buying a new audio output transformer. Typical for any 1939-42 Philco...those audio output transformers mounted under the chassis do not hold up as well as the older ones have that are mounted to the speaker.

But let's come back to that later.

Have you performed the "quick and dirty" test on the radio that I described previously? If not...please do so before going further. This should give some sort of indication of the health of your set's power transformer.

---

Re: Philco Model 41-296X with 41-285 modified chassis - jjbuzard - 12-02-2009

I have to order the 10MFD 160 volt capacitor I fried first, as per your instructions, should I also order another 84/6z4 (no way to test) and install it before proceeding :
These items won't be here before next week if I order them today. I might as well order the transformer and the Field Coil at the same time to save on shipping, right :

---

Re: Philco Model 41-296X with 41-285 modified chassis - Ron Ramirez - 12-02-2009

Remember, order a 10 mfd, 450 volt capacitor to replace the 10 mfd, 160 volt capacitor that fried!

I hate to see you ordering another tube when it may not be necessary...but do what you think best. At least should the original prove to be good later on, you'll have a spare...

You cannot order a field coil for your radio. It is a permanent part of the speaker and cannot be removed.

I suggest that, before ordering anything, you do this:

Remove that 84/6Z4 from its socket. That is the rectifier tube.

Disconnect the fried 10 uF 160 volt cap - taking careful notes as to how it hooked up before removing it.

Now perform that "quick and dirty" test I asked you to run, following the instructions I gave you in a previous post exactly as I laid them out. Keep in mind that in this test, the radio will not play. In this test, you don't want the radio to play; you are only checking the health of the power transformer.

Let us know how it turns out.

---

Re: Philco Model 41-296X with 41-285 modified chassis - jjbuzard - 12-02-2009

Yes I need a 10MFD 450 volt capacitor or filter (which term is more correct capacitor of filter? )and Yes I mean the Audio Output Transformer, the layout of the schematic is confusing, in actual physical layout in the chassis the audio output transformer is really next to the main transformer and the Field Coil is next to or part of the speaker, BUT the schematic has the Audio Output Transformer next to the speaker and the field coil (Labeled Field Coil) next to the main transformer, why is the schematic like this, :

So I need to replace the Audio Output transformer because of the large disparity of readings.

The field coil checks out almost perfect at 5 ohms across the 2 outer pins and 1000 across the 2 inner pins.

Will do quick and dirty test and report back

---

Re: Philco Model 41-296X with 41-285 modified chassis - jjbuzard - 12-03-2009

I did the quick and dirty as instructed, disconnected fried Capacitor and removed the 84/6Z4, (out of cabinet, speaker disconnected)
plugged the set in, no pow or poof, left it plugged in for 10-15 minutes, transformer remained cool,

Then I rechecked all readings on main transformer and Audio Output transformer with DIFFERENT OHM meter, results as follows, readings on schematic are in parenthesis. ( )

Main Transformer
White - White leads - 10 Ohms (12)
Black - Black -1 Ohm (-1)
Green - Green/Yellow -120 Ohms (160)
Green - Green/Yellow -75 Ohms (150)
I guess this means the main transformer is on its way out.

Audio Output Coil
White - Black/White 130 OHMS (190)
Black - black/White - 475 OHMS (170)

guess this means the Audio Output transformer is on its way out


The Field Coil
1080 Ohms ( 1100)
So it is good, HURRAH

So I will order parts today.

---

Re: Philco Model 41-296X with 41-285 modified chassis - Ron Ramirez - 12-03-2009

Well, Jim, it was good that you did not have any POW or POOF. Unfortunately, your resistance measurements tell the story - the high voltage winding of the power transformer is partially shorted out, and the primary of the audio output transformer is opening up.

So you know what you need to do.

At least you know your speaker is OK, so that is some good news.

Now to answer some of your other questions...

Quote:Yes I need a 10MFD 450 volt capacitor or filter (which term is more correct capacitor or filter?)

Electrolytic capacitor.

Quote:the layout of the schematic is confusing, in actual physical layout in the chassis the audio output transformer is really next to the main transformer and the Field Coil is next to or part of the speaker, BUT the schematic has the Audio Output Transformer next to the speaker and the field coil (Labeled Field Coil) next to the main transformer, why is the schematic like this, :

Again, schematics are sort of like road maps. However, unlike a conventional road map, a schematic diagram shows how everything is hooked up in a radio - it does not accurately reflect exactly how the wiring, parts, etc. are placed under the chassis. Once you gain experience in repairing radios, you will see that schematic diagrams are much, much easier to use than a pictorial of a set's under-chassis wiring - with a schematic, it is easier to see what each part is doing in each circuit of the radio.

Hang in there. You should be in the home stretch now; and with new transformers, hopefully that Philco will be playing Christmas music for you soon.

---

Re: Philco Model 41-296X with 41-285 modified chassis - Joe Rossi - 12-03-2009

jj, you should also note that while Pictorial Layouts of radios can be helpful, I've found that they are not always acurate. Like Ron wrote, once you become more familiar with reading and following the schematic the more sense it will make. Keep plugging away friend!

---

Re: Philco Model 41-296X with 41-285 modified chassis - jjbuzard - 12-03-2009

Parts are ordered, should be here in 3 - 4 days from Florida to Illinois. I was going to start replacing capacitors/wires while I waited but I see so many are on the same terminals as the items I am replacing, so I will wait and unwrap each terminal individually and wrap in the new parts/ wires at the same time. Maybe tackle some that are not associated with the new parts. I will take detailed digital pictures of each section before I start operating on the chassis, just as a visual reminder of how it goes.
Thanks. will keep you posted.

About the schematic, I just thought it odd that the field coil was so far away from the speaker when it is mounted on the speaker and the Audio Output was placed next to the speaker

---

Re: Philco Model 41-296X with 41-285 modified chassis - jjbuzard - 12-07-2009

I am in the process of replacing the capacitors that don't invole the wires to the transformer or the audio output coil, while I wait for the news transformer and coil to arrive.

I discovered if I look at replacing one capacitor at a time (where possible) it isn't such an overwhelming job, and I feel fairly confidant about going ahead on my own with this repair.

While I am at it I am replacing the rubber wires. I am finding the white wires are the worst for the wear.

To simplify the replacement process while I have one end of a wire undone that shares a terminal with a capacitor, I pull the wire out of the chassis, leaving the other end attached, straighten the wire out and gently twist the rubber insulation, if it doesn't fall apart, I continue to twist and gently pull until the rubber insulation starts to pull off the wire, then I pull the rubber insulation all the way off, then I slip a new piece of wire insulation from an OLD underground phone cable (about 18 gage wire) that I have laying around (all colors available) I have had this since I was 10 years old (it finally came in handy) To get the vinyl insulation off the original wire, I soak it in very hot water, it slips off easily after expanding, and then I slip it on the wire in the chassis, I then reroute the wire and resolder the loose end along with the capacitor. Do you foresee any thing wrong with this method :

---