[Ron Ramirez]

Here's tonight's progress report:

[Image: http://www.philcoradio.com/images/phorum...e00008.jpg]

Most of the wires have now been replaced. Of all the paper caps you see in the photo above, all are new (restuffed) save one. I have removed the electrolytic cans so they, too, may be restuffed.

Only a few resistors remain to be replaced.

The other original 0.2 uF paper cap's sleeve was too small to accommodate a new 0.22 uF film cap. So I looked around, and found an old Philco 0.25 uF paper cap which was much larger. This is what I used for the second 0.22 uF cap. You can see it in the photo above - it is the largest paper cap under the chassis.

[thirtiesradio]

Looks original. Very nice...
Good to get rid of that big electrolytic that was by the power transformer as well.

[sam]

very nice job ron

[klondike98]

lookin' good Ron

[Ron Ramirez]

I have rewired both IF transformers, polished both cans, and both are reinstalled in the chassis. Here's a look at the 1st IF transformer just before I put it back on the chassis:

[Image: http://www.philcoradio.com/images/phorum...e00009.jpg]

To disassemble this type of transformer, you have to remove the large adjustment heads which are screwed onto the threaded screws that adjust the slugs. It helps greatly to screw the slugs in several turns to make sure there is enough room to get the assembly out of the can. Count the turns and write these down. On this IF, I screwed each slug in 10 turns. Then you have to remove the two caps (for lack of a better term) which the adjustment screws go through; these hold the IF assembly onto the can.

Reassembly is the reverse of disassembly. You have to be really careful with these. The cans will not tolerate having those caps removed and reinstalled too many times. You can see the heavy scratches around the caps. One too many removals/reinstallations of these and the cans will simply break here. Don't ask me how I know.

Once reassembled, don't forget to screw the slugs back out again! Sure, you will have to align this transformer anyway, but you want to be able to pick up signals and not be left thinking that something else is wrong!

This is the first IF can I've ever seen that had the grid lead running on the outside of the can. The wire runs along the top of the chassis and then passes through one of the rivets which holds the IF tube socket in place, very close to the 7B7E grid pin.

I'm in the middle of rebuilding the dial lamp sockets. I still need to rebuild the electrolytic caps, also. But this one is getting close to completion.

[Ron Ramirez]

I have some questions regarding the power supply in this radio.

[Image: http://www.philcoradio.com/images/phorum...730_ps.jpg]

Note the parts circled in red - resistors (78) and (79), and capacitors (73) and (74).

Two 150K resistors between each side of the AC line and ground instead of the usual .01 uF caps?

And, more puzzling to me, two .003 uF caps between each side of the rectifier plates and ground?

Your comments, please. I am inclined to leave these parts out unless overruled by you, my valued and respected Phellow Phorum members.

[Arran]

Ron;
  If it appears to have left the factory with part 78 and 79  in place there must be a reason for them, though that's the first time that I have seen a pair of resistors between each leg of the power transformer primary and ground, a pair of capacitors is more normal. As for the ones on the plates of the rectifier tube, parts 73 and 74, maybe those are there to remove some sort of power line transient that was common in South American countries at the time?
Regards
Arran

[morzh]

Ron

I myself was surprised to see this arrangement when I looked at it yesterday.

Now, potentially the resistors might be used to discharge the interwinding capacitance, I am not sure why, but suppose this is an especially capacitive xfmr that gets charged to some voltage that can give you a little tickle, someone complained and they decided to discharge it.

The caps.....this might be a way to do the line RF filtering without exposing caps to the MAINs directly, so to avoid the danger of breakdown and completing the circuit between MAINs and GND.

Just a shot in the dark.

[Arran]

 One thing I should add about my capacitor re-stuffing method, the type of corrugated cardboard I have been using is a thinner type, with two layers, I think it used to be a box for an ornament of some kind. It tends to bend easier then the type you would run into for something like a moving box, and if it ends up being too think you can peel away the layers. As I mentioned I cut the cardboard into strips, like maybe 1'' wide, usually a little wider then the body of the capacitor is long. Then I tack one end down with hot glue to the cap body where the cap body is roughly in the center of the strip, then I warp the strip around the body of the cap, cut it to length, then tack that down too if needed. Then you take the whole affair and stuff it into the old cardboard tube until it's centered between the ends, if it won't go in peel a layer off the cardboard and try again.
 Then you take the glue gun and start injecting glue into one end, a little at a time, till it's filled. But one thing you need to do is wait until one side cools and hardens before you fill the other side, so you need some way of holding it up on end until it does, so normally I restuff three or more tubes at a time so the first is cooled by the time I've finished with the third or forth. If I'm in a hurry, or the cap is of a large diameter like a toilet paper roll electrolytic, I will put it in the freezer.
 This is something that isn't all that hard to do, it just takes some practice and experience to refine. For example I prefer to melt out paper caps in a toaster oven set to 250 centigrade, a heat gun works but you can scorch the paper labels if you are not careful. Believe it or not I have a small stockpile of paper capacitor tubes that I cleaned out in advance just for future projects, usually along with ones belonging to whatever set I am restoring, since the toaster oven was already hot.
  One thing that I have been trying to find though is a source of cardboard or paper tubes of the right diameter and wall thickness to use as a substitute for the originals, like for sets where many or all of the originals are gone. I thought maybe the kind they use for firecrackers might work but  I think that the walls are too thick.
Regards
Arran

[Ron Ramirez]

Ron;
  If it appears to have left the factory with part 78 and 79  in place there must be a reason for them, though that's the first time that I have seen a pair of resistors between each leg of the power transformer primary and ground,

Now, potentially the resistors might be used to discharge the interwinding capacitance, I am not sure why, but suppose this is an especially capacitive xfmr that gets charged to some voltage that can give you a little tickle, someone complained and they decided to discharge it.

Yes, this set had the resistors, but one was connected across the line instead of from one side of the line to ground!

Okay, you guys have convinced me about the resistors, and I'll put new ones in their place - only they will be connected between each side of the line and ground as the schematic indicates.

I was thinking along the same lines as Arran regarding caps (73) and (74):

As for the ones on the plates of the rectifier tube, parts 73 and 74, maybe those are there to remove some sort of power line transient that was common in South American countries at the time?

In any event,  I have decided to leave those two caps out. So now, all of the paper caps have been replaced with new caps stuffed inside original (or original-type) sleeves. All resistors save three (78 and 79, plus one other) have been replaced. The dial lamp sockets are rebuilt. I only need to rebuild the electrolytic condenser cans, reinstall those, and attach a power cord and it will be ready to try out.

[morzh]

3nF to remove power transients....don't think so. Noise maybe, transients - this is what a large inductance, large capacitance and transient absorbers like TVS, MOV and such are for.
3nF will filter RF noise or in a DCDC converter will prevent common mode radiation as a bridge cap, but not your typical transient.


BTW, I never implied I hought any of these ingenious dohikeys were necessary. Especially the resistors.

[mikethedruid]

I think you are wise connecting the resistors 78 and 79 and shown in the schematic. One other thing that occurs to me is that with the windings of the transformer, they form an RL circuit, and become a path to ground for interference. I think the caps serve to further filter RF to ground, as morzh observed. I would recommend using them as they are shown in the schematic.

[Arran]

 They had some weird stuff back then that doesn't really exist anymore that would cause all sort of interference, like diathermy machines, street cars, etc. They also did used to use power lines for communications purposes more so then now, although I think they still do for fire alarms. I think you could leave any or all of them out and it would not make any difference, but it's curious how they added them on each leg of the high voltage winding, maybe they were trying to create an LC circuit for filtering higher frequency noise that might get through?
Regards
Arran

[Ron Ramirez]

I would recommend using them as they are shown in the schematic.

Frankly, if I were to replace the .003 uF caps, I would want to use X/Y safety caps...but these would need to withstand a constant 320+ volts AC instead of the usual 125. I'm just going to skip 'em. They were in very tight quarters anyway, and installing new ones would be difficult - it was hard enough getting the old ones out without burning adjacent power transformer leads. I know I could just use regular 630 or 1000 volt film caps, but I'd rather not take the chance of them failing shorted, in spite of the fact that the radio will only be used infrequently once finished.

BTW, I never implied I thought any of these ingenious dohikeys were necessary. Especially the resistors.

I know, lighten up, man.

[morzh]

Ron

You do not need to use X/Y safety for those 3nF unless you want to. Y safety is there to ensure you do not become connected to Mains. In this case the caps are on the secondary side of the transformer so even if they break down you do not become exposed to MAINs, it would take both transformer and the cap to fail short and this is a double failure.

Simple cap with appropriate voltage rating will do.