[skyscraper]

Hi everyone, this is my first post here, but I've been lurking for quite a while. My name is Will, I'm 18 years old, and have recently gotten into restoring old radios. I started out with my grandfather's Zenith H723Z1 tabletop, recapped it and got it working really well. Then around Thanksgiving I found an 89 cathedral at a garage sale for $5 that I'm working on now. For Christmas I received a beautiful 40-190 skyscraper, and I also have a Trutone D-911 in bad condition. I'm completely hooked, and having a great time. This forum has been one of my primary resources, I hope you don't mind a few newbie questions

I'd like to get a little help restoring the 89 here as I go along. So far I've tested the transformer (leaked a little wax and hums slightly, but all windings are good at the right voltages), the speaker coils, repaired the cone, recapped 3 out of the 8 bakelite caps, replaced the cord with a great looking rayon reproduction, and powered up the transformer with a dim-bulb tester.
Without the tubes, the pilot light came on and all the voltages were correct, and when the B+ line was disconnected, I measured about 400v DC off the 80 tube. So far everything is going well.

I have two questions right now. First, is there any way to test the speaker? I'm not sure what voltages to use, but with 100v on the field coil and a gentle audio source on the transformer you can hear the sound faintly. With the audio source directly on the speaker it's a bit louder but still quite faint. I know the impedances don't match up on either. If the speaker is broken I'll move on to another radio, I can't afford to replace it.

Second, while restuffing bakelite blocks I found a capacitor that isn't on the schematic. Looking at 89 Scematic, it is connected to the plate of the 75 tube and ground. It is a brown half inch square Micamold cap, with a single yellow dot on one side. It looks like it was likely soldered on later, perhaps to try to replace part 30 (also replaced with a paper tube cap), but soldered onto the wrong lugs of the block. Is there any reason to replace it, or should I just leave it out?

This 89 is the first revision code 123. My goal is to make it look as original as possible, so I'm restuffing everything and using cloth wire where possible.

Great forum, thanks for all the good information!

[Mondial]

Have you checked the resistance of the speaker's field coil winding? Applying 100 VDC while testing it will not make it work if the field winding is open. With an open coil you may still hear very low audio from residual magnetism in the iron core.

What signal source are you using to check the speaker for sound? If you are hearing anything at all through the output transformer, then chances are the voice coil and transformer are probably ok.

The additional mica cap across the 75 plate to ground is not really necessary for operation, but you might want to reinstall it. It might have been added as an RF bypass, or to modify the tone characteristics of the radio by rolling off the high audio frequencies. It appears that this cap ( 250 pF ) was added in later production and is shown on this schematic:

http://www.nostalgiaair.org/PagesByModel...013877.pdf

[skyscraper]

Thanks for the reply.

Yes, all are in line with the schematic. The audio supply was from an 8 ohm stereo, and since I don't know the impedance of the cone coil, I put a high watt resistor of a few ohms in series. Sound was audible, but not loud. Nothing without the field coil energized.

Ah I see, I guess I didn't go far enough in revisions. Thanks. Some Micamold capacitors are paper, correct? Should it be replaced or just soldered back in?

[Mondial]

Micamold did not make paper capacitors that style until the 1940's so the original cap can be reinstalled. It is a true mica cap and of high quality.

Unfortunately it seems all Micamold caps are being condemned these days because of the reputation of the later paper types, which looked similar to the genuine micas.

[klondike98]

Welcome to the Phorum Skyscraper!

[skyscraper]

Thanks, Bob!

Mondial - Thanks for the info, I'll put it back then.

When you're rewinding coils (I haven't checked mine yet), is the exact wire gauge important? From what I've read it sounds like at least the osc tickler needs to be cooked and rewound. I have a large spool of 30awg, but nothing else. Can I get away with it? I can't find the specs, but I think the original was supposed to be slightly thinner.

Also, does anyone know what type of rubber grommets to buy for under the tuning cap?


EDIT: I've started testing the coils, so far the primary on the detector coil and the tickler on the oscillator coil are out. Great. Is there a list somewhere of the number of turns and gauge of these coils?

[tab10672]

There is a page somewhere around here that explains the process check philco repair bench

[skyscraper]

I've looked for such a page, but haven't found one. I know the basic procedure of cooking, winding and lacquering, but a list of wire gauge and turns would be extremely helpful. I've seen 36 gauge mentioned on another forum for the osc tickler, would this work? http://www.ebay.com/itm/Magnet-Wire-36-A...3a78df33dc

The coils aren't by any chance all the same gauge, are they?

I figured out what I was doing wrong with the speaker yesterday, managed to hook it up, and it sounds great! I didn't have very high hopes with the number of tears and the condition of the paper, but some tacky fabric glue and a coffee filter made it sound like new. I'm very impressed.

[skyscraper]

The osc coil is 38awg, thanks Ron. It would still be extremely helpful if anyone knew the size for the other coils. It's the second, not sure what it is called. Once they get smaller than 30 or so I have a hard time differentiating.

I'm making progress. I recaped the tone control and filter block, and 6/8 bakelite blocks. I've also ordered cloth wire and replacement resistors for a few out of tolerance. Is it alright to reuse the 200ohm wire resistor pack that was in one of the blocks? It is only 9% off value.

One last thing, is the whiskey rayon grille cloth an acceptable replacement? I can't find a good picture of the original. That's the closest I can match my couple of tatters.

[Ron Ramirez]

a list of wire gauge and turns would be extremely helpful

You're asking for something that does not exist. Someone would have to spend a LONG time...years...with no job or anything else to do but remove coils from Philco radios, unwind, measure wire diameters (with a micrometer) and count number of turns, rewind. And Philco made a lot of different radios.

The coils aren't by any chance all the same gauge, are they?

Nope. The inner winding on the outer form is, I think, 30 or 31 gauge. I do not remember offhand what gauge the tertiary winding (on the inner core) is.

[skyscraper]

Thanks for your reply, Ron. I was hoping Philco or Riders had published something, I guess that answer is no. I'll contribute whatever I find. Is it possible the set would still work with a coil one or two AWG off?

[morzh]

Good news is, a gauge rarely matters much. As long as you observe the number of turns and the current withstanding capability (which considering low tubes' currents does not need to go to amps at all) most wires will do. Of course if you have lots of turns you have to worry about the available space, but typically turns are not many.

[skyscraper]

Thanks morzh, that's exactly what I wanted to hear ;) Between a reel of 30 and 36 or 38 I think I have it covered.

Getting closer now. Tonight I'm going to try hacking into the electrolytic cans, which sound to still be almost filled with electrolyte. Expecting a mess..

[OldRestorer]

Well,
As an electric novice I can tell you that the whiskey rayon is not a brownish bronze like it looks . It is yellow goldish but I can tell you nothing about your chassis. oh wait, make sure your Ecaps are properly installed using the arrows on the side. there you go, I learned something. I wish I had learned this all at 18.

Kirk L

[skyscraper]

Hi Kirk,

Darn.. That's the only thing that looks remotely like the original, but it was definitely dark/brownish colored.

Yep, thanks for the tip. After a few disasters in my other hobby (homebrew 8 bit computers), I've learned well to observe polarity
Now, if I could only stop forgetting to leave my multimeter lead plugged into amps when I'm trying to measure voltage... That was the first time I was truly thankful for the dim bulb tester.

I'm taking a brief break while waiting on a Radio Daze order, and have started learning the theory behind tube circuits. Today I designed and built a rudimentary iPod amplifier around a single 41 tube, it works and sounds great. There is a purple glow around the plate in the dark, which I think means it's a bit gassy? I am driving it about as hard as it will go. Lots of fun.

The problem with having these crazy hobbies is they are pretty much a loner game. I wouldn't think there are more than a handful of kids my age on earth who spend their weekends tinkering with tubes and fixing radios older than their grandparents. But if I decide to go into electrical engineering, I guess I'll have a bit of a jump on the rest of the crowd. ;)